Engineering 
 Library 
 
Copies of this report my be purchased 
 at one dollar eaoh from the Secretary of . 
 the American Institute of Electrical Engi- 
 neers, 33 West 39th Street, New York, N.Y. 
 
REPORT 
 
 OF THE 
 
 AMERICAN COMMITTEE 
 ON ELECTROLYSIS 
 
 1921 
 
i?C ->* 
 
 Engineering 
 
 y.P-ary 
 
 
COMMITTEE 
 
 American Institute of Electrical Engineers 
 BION J. ARNOLD, Chairman, Chicago, Illinois. 
 
 N. A. CARLE, Newark, New Jersey. 
 
 F. N. Waterman, New York, N. Y. 
 
 American Electric Railway Association 
 L. P. CRECELIUS, Cleveland, Ohio. 
 
 W. J. HARVIE, Syracuse, N. Y. 
 
 G. W. VAN DERZEE, Milwaukee, Wisconsin. 
 
 American Railway Engineering Association 
 
 E. B. KATTE, New York, N. Y. 
 MARTIN SCHREIBER, Newark, New Jersey. 
 W. M. VANDERSLUIS, Chicago, Illinois. 
 
 National Electric Light Association 
 L. L. ELDEN, Boston, Mass. 
 
 D. W. ROPER, Treasurer, Chicago, Illinois. 
 PHILIP TORCHIO, New York, N. Y. 
 
 American Gas Association 
 
 WALTER C. BECKJORD, New York, N. Y. 
 
 CHARLES F. MEYERHERM, New York, N. Y. 
 
 H. C. SUTTON, Philadelphia, Pa. 
 
 Natural Gas Association of America 
 FORREST M. TOWL, New York, N. Y. 
 
 THOMAS R. WEYMOUTH, Oil City, Pa. 
 
 S. S. WYER, Columbus, Ohio. 
 
 American Telephone and Telegraph Company 
 A. P. BOERI, New York, N. Y. 
 
 F. L. RHODES, New York, N. Y. 
 H. S. WARREN, New York, N. Y. 
 
 American Water Works Association 
 ALFRED D. FLINN, New York, N. Y. 
 
 NICHOLAS S. HILL, JR., New York, N. Y. 
 
 E. E. MINOR, New Haven, Conn. 
 
 National Bureau of Standards 
 
 BURTON McCoLLUM, Washington, D. C. 
 
 DR. E. B. ROSA,* Secretary, Washington, D. C. 
 
 E. R. SHEPARD, - Washington, D. C. 
 
 * Deceased. 
 
6 PREFACE 
 
 organizations they represent will aid materially in reducing the 
 destructive effects due to electrolysis. 
 
 The Committee, through its Research Subcommittee, has 
 established a close working relationship with the National Bureau 
 of Standards, which has been distinctly advantageous. 
 
 The Committee regrets to chronicle the death in Washington 
 on May 17, 1921, of its secretary, Dr. Edward B. Rosa, Chief 
 Physicist of the National Bureau of Standards, one of its most 
 efficient and esteemed members. 
 
 October, 1921. 
 
 BION J. ARNOLD, 
 
 Chairman. 
 
TABLE OF CONTENTS 
 CHAPTER 1. Principles and Definitions 
 
 Page 
 
 A. Electrolysis in General: 
 
 1. Electrolysis 15 
 
 2. Electrolyte, Electrode, Anode, and Cathode 15 
 
 3. Amount of Chemical Action 15 
 
 4. Cause of Current Flow 16 
 
 5. Electrolysis by Local Action 16 
 
 6. Anodic Corrosion 16 
 
 7. Secondary Reactions 16 
 
 8. Cathodic Corrosion 17 
 
 B. Electrolysis of Underground Structures. 
 
 9. General 17 
 
 10. Self Corrosion 17 
 
 11. Acceleration of Local or Self Corrosion 17 
 
 12. Stray Current 18 
 
 13. Anodic and Self Corrosion 18 
 
 14. Coefficient of Corrosion 18 
 
 15. Passivity 18 
 
 16. Polarization Voltage 18 
 
 17. Alternating or Frequently Reversed Direct Currents 19 
 
 18. Action on Underground Metallic Structures 19 
 
 19. Electrolysis Mitigation ". / 19 
 
 20. Electrolysis Survey 20 
 
 2 1 . Overall Potential Measurements ' 20 
 
 22. Potential Gradient 20 
 
 23. Potential Difference. ; 21 
 
 24. Arithmetical Average 21 
 
 25. Algebraic Average 21 
 
 26. Positive and Negative Areas 21 
 
 27. Drainage System 21 
 
 28. Uninsulated Track Feeder System 22 
 
 29. Insulated Negative Feeder System 22 
 
 CHAPTER 2. Design, Construction, Operation and Maintenance 
 
 1. Measures Tending both to Railway Economy and the Reduction 
 
 of Stray Current 24 
 
 2. Measures Employed Solely for Electrolysis Prevention 24 
 
 (a) Applicable to Railways. 
 
 (b) Applicable to Affected Structures. 
 
 (c) Interconnection of Affected Structures and Railway 
 
 Return Circuit. 
 
 I. RAILWAYS 
 
 A. Features Which Affect Electrolysis Conditions. 
 
 1. Track Construction and Bonding 25 
 
 (a) Importance of Rail Circuit 25 
 
CONTENTS 
 
 Page 
 
 (b) Rail Bond Resistance and Tests 25 
 
 (c) Types of Bonds 26 
 
 Soldered Bonds 26 
 
 Brazed or Welded Bonds 26 
 
 Resistance Weld 26 
 
 Electric Arc Process 27 
 
 Oxy-Acetylene Process 27 
 
 Pin Expanded Terminal Bonds 27 
 
 Compressed Terminal Bonds 27 
 
 (d) Welded Rail Joints 28 
 
 Electric Rail Welding 28 
 
 Arc Welding 28 
 
 Cast Welding 28 
 
 Thermit Process 28 
 
 (e) Cross-Bonding 29 
 
 (f ) Special Track Work Bonding 29 
 
 (g) Bonding Tracks with Signal Systems 30 
 
 (h) Conductivity and Composition of Rails 30 
 
 2. Track Insulation 31 
 
 (a) Degrees of Insulation 31 
 
 Substantial Insulation 31 
 
 Partial Insulation 31 
 
 (b) Leakage to be Expected 32 
 
 3. Reinforcement of Rail Conductivity 32 
 
 4. Power Supply 33 
 
 (a) High Voltage d. c. Railways 34 
 
 (b) Source of Stray Currents 34 
 
 (c) Relation of Feeding Distance to Stray Currents and 
 
 Overall Voltages 38 
 
 (d) Economic Considerations Involved in Additional Supply 
 
 Stations 42 
 
 (e) Automatic Substations 44 
 
 (f) Location of Supply Stations 46 
 
 (g) Alternating Current Systems 46 
 
 5. Interconnection of Tracks. 47 
 
 B. Features of Railway Construction and Operation Employed for 
 
 Electrolysis Mitigation. 
 
 1 . Insulated Negative Feeder System 49 
 
 (a) Description 49 
 
 (b) Application of Insulated Negative Feeders 53 
 
 Application to Interurban Lines 55 
 
 (c) Negative Boosters 57 
 
 2. Three-Wire System 57 
 
 (a) Description 57 
 
 (b) Insulation of Trolley Sections 59 
 
 (c) Costs 59 
 
 (d) Difficulties and Limitations 60 
 
 (e) Practicability 61 
 
 (f ) Extent of Adoption 62 
 
CONTENTS 9 
 
 Page 
 B. Features of Railway Construction (continued) 
 
 3. Reversed Polarity Trolley System 62 
 
 4. Periodic Reversal of Trolley Polarity .... 63 
 
 5. Double Contact Conductor Systems 65 
 
 II. UNDERGROUND STRUCTURES SUBJECT TO INJURY BY 
 
 STRAY CURRENTS 
 
 A. Location with Respect to Tracks. 
 
 B. Cable Systems. 
 
 1. Avoidance of Accidental Contacts with Other Structures. . . 66 
 
 2. Conduit Construction 67 
 
 (a) Signal Cables 67 
 
 (b) Power Cables 68 
 
 3. Surface Insulation 69 
 
 4. Insulating Joints 70 
 
 C. Pipe Systems 
 
 1 . Surface Insulation 71 
 
 2. Insulating Joints 74 
 
 (a) New Work 74 
 
 (b) Cement Joints 76 
 
 (c) Leadite and Metallium 76 
 
 (d) Dresser Couplings 78 
 
 (e) Special Insulating Joints 78 
 
 (f ) Insulating Joints Applied to Existing Pipe Lines 78 
 
 3. Shielding 79 
 
 III. MEASURES INVOLVING INTERCONNECTION OF AFFECTED 
 
 STRUCTURES AND RAILWAY RETURN CIRCUIT 
 
 A. Electrical Drainage of Cable and Pipe Systems 81 
 
 1. Drainage of Cable Sheaths 83 
 
 (a) Method of Draining Cables 83 
 
 (b) Heating Effect of Stray Current on Cable Sheaths 84 
 
 2. Difference Between Cable Drainage and Pipe Drainage 88 
 
 3. Application of Drainage to Pipes 90 
 
 (a) Maintaining Pipes Negative to Earth 90 
 
 (b) Effect of Pipe Drainage on Current Interchange 90 
 
 (c) Effects of Different Kinds of Pipes and Joints 92 
 
 SUMMARY OF GOOD PRACTICE. 
 
 A. Railways 92 
 
 1. Track Construction and Bonding 92 
 
 2. Track Insulation 93 
 
 3. Reinforcement of Rail Conductivity 93 
 
 4. Power Supply 94 
 
 5. Interconnection of Tracks : 94 
 
 6. Insulated Negative Feeder System 94 
 
 7. Three-wire System 95 
 
 8. Reversed Polarity Trolley System 95 
 
 9. Periodic Reversal of Trolley Polarity 96 
 
 10. Double Contact Conductor Systems 96 
 
 11. Alternating Current Systems 96 
 
10 CONTENTS 
 
 Page 
 
 B. Affected Structures. 
 
 1. Location with Respect -to Tracks 96 
 
 2. Avoidance of Contact with Pipes and Other Structures 96 
 
 3. Conduit Construction 97 
 
 4. Insulating Joints in Cable Sheaths 97 
 
 5. Surface Insulation of Pipes and Cables 97 
 
 6. Insulating Joints in Pipes 97 
 
 7. Shielding 98 
 
 C. Interconnection of Affected Structures and Railway Return 
 
 Circuit. 
 
 1. Cable Drainage 98 
 
 2. Pipe Drainage 99 
 
 CHAPTER 3. Electrolysis Surveys 
 I. INTRODUCTION 
 
 A. Purpose and Scope of Electrolysis Surveys. 
 
 1. Purpose of Electrolysis Surveys 100 
 
 2. Difficulty of Standardizing Survey Procedure 100 
 
 3. Information Obtainable by Electrolysis Surveys 100 
 
 B. Types of Surveys 101 
 
 C. General Preliminary Data. 
 
 1. Data on Underground Structures 102 
 
 2. Data on Railway Systems 102 
 
 D. Cooperation in Making Surveys 102 
 
 II. ELECTRICAL MEASUREMENTS 
 
 A. Voltage Surveys 103 
 
 1. Measurement of Maximum Potential Drop Along Railways.. 104 
 
 (a) Importance of Maximum Potential Drop Measurements. 104 
 
 (b) Procedure in Making Maximum Drop Measurements. . 104 
 
 2. Potential Gradient Measurements 106 
 
 (a) Scope of Term 106 
 
 (b) Measurement of Potential Gradients in Tracks 106 
 
 3. Measurement of Potential Differences 107 
 
 (a) Purpose of Measurement of Potential Differences 107 
 
 (b) Procedure in Making Measurements of Potential Differ- 
 ences 107 
 
 B. Current Surveys. 
 
 1. Scope and Importance of Current Surveys 108 
 
 2. Measurement of Currents in Feeders and Rails 109 
 
 (a) Purpose of Measuring Feeder and Rail Currents 109 
 
 (b) Procedure in Measuring Current in Feeders and Rails . 109 
 
 3. Measurement of Currents in Pipes and Cable Sheaths 110 
 
 (a) Purpose and Importance of Pipe Current Measurements. 110 
 
 (b) Selection of Points of Measurement 110 
 
 (c) Methods of Measuring Current Flow in Pipes Ill 
 
 Drop in Potential Method 113 
 
 Qalibration of Pipes 113 
 
 Use of a Direct-Current Ratio Relay 115 
 
 4. Comparing Currents Under Different Conditions 115 
 
CONTENTS II 
 
 Page 
 
 5. Measurement of Current Flowing from Underground Struc- 
 tures to Earth 115 
 
 (a) Differential Current Measurements 116 
 
 C. Miscellaneous Tests. 
 
 1. Track Testing 116 
 
 (a) Inspection 116 
 
 (b) Use of Portable Bond Tester '. . 117 
 
 (c) Autographic Method of Bond Testing 117 
 
 (d) Testing of Cross-bonds and Special Work 117 
 
 2. Measurement of Leakage Resistance Between Tracks and 
 
 Underground Structures 119 
 
 (a) Importance of Tests of Roadbed Resistance 119 
 
 (b) Differential Method of Measuring Roadbed Resistance. 119 
 
 (c) Isolation Method of Measuring Roadbed Resistance. . . 121 
 
 3. Location and Testing of High Resistance Joints in Pipes 122 
 
 4. Tracing the Source of Stray Currents 123 
 
 5. Location of Unknown Metallic Structures or Connections. . . 123 
 
 III. INTERPRETATION OF RESULT^ OF ELECTROLYSIS 
 SURVEYS 
 
 A. Interpretation of Potential Measurements. 
 
 1. Maximum Voltages and Track Gradients 124 
 
 2. Potential Difference Measurements 125 
 
 B. Interpretation of Current Measurements on Underground 
 
 Structures. 
 
 1. Relation of Stray Current to Corrosion 125 
 
 2. Relation of Current to Fires and Explosions 126 
 
 C. Interpretation of Measurements of Current Flowing from 
 
 Structures to Earth 126 
 
 D. Use of Reduction Factors 127 
 
 E. Effect of Reversals of Polarity. 
 
 1. Polarity of Pipes Always the Same 128 
 
 2 . Polarity of Pipe Changing with Long Periods of Several Hours. 128 
 
 3. Polarity of Pipes Reversing with Periods of Only a Few 
 
 Minutes 128 
 
 4. Polarity of Pipes Reversing with Periods of From Fifteen 
 
 Minutes to One Hour 129 
 
 IV. SELECTION OF INSTRUMENTS 
 
 A. Portable Measuring Instruments 129 
 
 B. Recording Instruments 130 
 
 V. RECORDS AND REPORTS: 
 
 A. General Discussion : . . . 131 
 
 B. Electric Railways 131 
 
 C. Piping Systems 132 
 
 D. Cable Systems 132 
 
 E. Bridges and Buildings 132 
 
 F. General Conditions 132 
 
 VI. TABLES... . 133 
 
12 CONTENTS 
 
 Page 
 
 CHAPTER 4. European Practice 
 
 A. General 134 
 
 B. Laws and Regulations. 
 
 1. Germany 135 
 
 (a) Commission Recommendations 136 
 
 2. Italy 136 
 
 3. France 136 
 
 4. Spain 137 
 
 5. Great Britain 137 
 
 C. Construction Characteristics. 
 
 1. General 138 
 
 2. Rails 140 
 
 3. Rail-Bonds 141 
 
 Table 7. Rail Bonding (United Kingdom) 143 
 
 4. Cross-Bonds 143 
 
 5. Roadbed Construction 143 
 
 6. Feeders. . '. 147 
 
 7. Negative Boosters 148 
 
 Table 8. Use of Negative Boosters (United Kingdom) 148 
 
 8. Double Trolley 149 
 
 9. Three-wire System 1 49 
 
 10. Negative Trolley 149 
 
 11. Pilot Wires 150 
 
 12. Bond Testing . . . 150 
 
 13. Pipes and Pipe Joints 150 
 
 14. Depth of Pipes Below Surface 150 
 
 15. Mains on Both Sides of Streets 151 
 
 16. Insulating Coverings for Pipes 151 
 
 17. Electric Cables 151 
 
 D. Electrolysis Conditions. 
 
 1. General 151 
 
 2. Voltage and Current Conditions : Experience with Electrolysis. 152 
 
 (a) Germany 152 
 
 (b) Italy 153 
 
 (c) France 153 
 
 (d) Great Britain 154 
 
 E. Miscellaneous Observations. 
 
 1. Drainage System 155 
 
 2. Corrosive Effects of Soil; Earth Resistance 155 
 
 3. Electrolysis Testing Methods 156 
 
 4. Economic Aspects of the Electrolysis Problem 157 
 
 5. Application to American Conditions , 157 
 
 F. Summary 158 
 
 G. European Regulations Adopted and Proposed. 
 
 Germany 159 
 
 Sec. 1. Application of Rules 159 
 
 Sec. 2. Rail Conductors 162 
 
 Sec. 3. Rail Potential 165 
 
 Sec. 4. Resistance between Rail and Earth .. . 170 
 
CONTENTS 13 
 
 Page 
 G. European Regulations Adopted and Proposed (continued) 
 
 Germany (continued) 
 
 Sec. 5. Current Density 172 
 
 Sec. 6. Control 175 
 
 France 176 
 
 England 177 
 
 Spain 183 
 
 CHAPTER 5. Electrolysis Research 
 
 Further Work Necessary to Arrive at a Solution of the Engi- 
 neering Problem. 
 
 1. Methods of Testing '. . 184 
 
 2. Effect of Different Rail Voltage Drops 185 
 
 3. Studies of Electric Railway Power Distribution 185 
 
 4. Study of Mitigative Measures Applicable to Affected Struc- 
 
 tures 185 
 
 5. Determination of Safety Criterion for Pipes Where Positive 
 
 to Earth 185 
 
 6. Self Corrosion 186 
 
 7. Fire and Explosion Hazard on Gas and Oil Pipes 186 
 
 8. Heating of Power Cables Due to Stray Currents on Sheaths. 186 
 
 Summary 187 
 
 BIBLIOGRAPHY 
 
 General 188 
 
 Electrolytic Corrosion of Pipes and Cables 188 
 
 Surveys and Measurements 189 
 
 Alternating Current and Periodic Current Electrolysis 189 
 
 Reinforced Concrete 189 
 
 Track Construction, Track Leakage, and Rail Bonding 189 
 
 Insulated Negative Feeders 190 
 
 Automatic Substations 190 
 
 Three-Wire Operation 191 
 
 Insulating Pipe Coverings 191 
 
 Insulating Joints 191 
 
 Pipe and Cable Drainage 191 
 
 Legal Aspects 192 
 
 APPENDIX 
 
 Tables of Current Data for Rails and Pipes 193 
 
 Sample Data Sheets 200 
 
LIST OF ILLUSTRATIONS 
 
 Page 
 Figure 1. Single Trolley Electric Railway Showing Paths of Return 
 
 Current 35 
 
 Figure 2. Potential Profile of Railway System 36 
 
 Figure 3. Potential Profile Showing Rails and Pipes without Connec- 
 tions Between Pipes and Railway Return Circuit 37 
 
 Figure 4. Effect of Feeding Distance on Stray Current 39 
 
 Figure 5. Effect of Feeding Distance on Overall Voltages and Poten- 
 tial Difference Between Earth and Rails 40 
 
 Figure 6. Reduction of Track Voltage Drop by Additional Power Sup- 
 ply Stations 41 
 
 Figure 7. Relation of Number of Substations to Annual Charges, for 
 
 Interurban Line 43 
 
 Figure 8. Potential Profile of Two Independent Railway Systems 
 
 Showing Effect of Interconnection 48 
 
 Figure 9. Overall Voltage Curves, No Feeders 50 
 
 Figure 10. Equi-Potential Insulated Negative Feeder System 50 
 
 Figure 11. Insulated Negative Feeders Applied to City Net- work of 
 
 Tracks 52 
 
 Figure 12. Graded Insulated Negative Feeder System 54 
 
 Figure 13. Insulated Negative Feeders Applied to Interurban Lines. . . 56 
 
 Figure 14. Parallel Three-Wire System ' 58 
 
 Figure 15. Sectionalized Three-Wire System .- . . . 58 
 
 Figure 16. Variation of Coefficient of Corrosion of Iron with Frequency. 64 
 
 Figure 17. Cross-Section of Insulating Joint for Power Cable Sheaths. 72 
 Figure 18. Showing Necessity of Installing Insulating Joints in Services 
 
 Connected to Mains Laid with Insulating Joints 75 
 
 Figure 19. Type B Bell for Cast Iron Pipe, Designed for Cement Joints . 77 
 Figure 20. Service Pipes Being Damaged Under Car Tracks by Elec- 
 trolysis 80 
 
 Figures 21 and 22. Methods of Installing Leads for Current Test 
 
 Station 112-114 
 
 Figure 23. Differential Method of Making Roadbed Resistance Meas- 
 urements 118 
 
 Figure 24. Method of Making Roadbed Resistance Measurements on 
 
 Open Track Construction 120 
 
 Figure 25. German Tramway Rails 139 
 
 Figure 26. British Tramway Rails 140 
 
 Figure 27. Rail Weight Data 141 
 
 Figure 28. Typical Rail Bonds United Kingdom 142 
 
 Figure 29. Cross-Bonding Details, etc. United Kingdom ." 144 
 
 Figure 30. Track Construction United Kingdom 145 
 
 Figure 31. Track Construction and Rails Germany 146 
 
 Figures 32 and 33. Key to Calculation of Voltage Drop in Rails 168 
 
 14 
 
CHAPTER 1 
 
 PRINCIPLES AND DEFINITIONS 
 A. ELECTROLYSIS IN GENERAL. 
 
 1. Electrolysis is the process whereby an electric current pass- 
 ing from an electrode to an electrolyte or vice versa causes chemical 
 changes to take place in the electrolyte. Electrolysis also in- 
 cludes any chemical changes at the surface of an electrode re- 
 sulting from the chemical changes in the electrolyte. Electrolysis 
 is independent of the heating effect of the electric current. 
 
 NOTE. These changes usually occur in a water solution of 
 an acid, alkali, or salt. By the passage of an electric current 
 through it, water (containing a trace of acid) is decomposed 
 into hydrogen and oxygen, copper is deposited from a solution 
 of copper sulphate, silver from solutions of silver salts. 
 Electroplating, electrotyping, and refining of metals by 
 electrodeposition are useful applications of electrolysis in 
 the arts. Electrolysis is involved in the charge and discharge 
 of storage batteries, and in the operation of primary batteries. 
 
 In order that electrolysis may occur, the following condi- 
 tions must be present : 
 
 (a) There must be a flow of electric current through a 
 conducting liquid from one terminal to another ; 
 
 (b) The conducting liquid must be a chemical compound 
 or solution which can be altered by the action of the electric 
 current. 
 
 2. Electrolyte, Electrode, Anode, Cathode. The electrolyte is 
 the solution (or fused salt) through which the electric current 
 flows; the conducting terminals are the electrodes; the terminal 
 by which the current enters the solution is the anode; the terminal 
 by which it leaves is the cathode. 
 
 NOTE. The chemical changes caused by the current may 
 affect both the electrolyte and the electrodes. In the case 
 of a solution of copper sulphate with copper plates as elec- 
 trodes, copper is removed from the anode by the current 
 and carried into solution; an equal amount of copper is 
 deposited upon the cathode. In general the metal travels 
 with the current toward the cathode. 
 
 3. Amount of Chemical Action. (Faraday's Law.) The amount 
 of chemical action taking place at the anode and also at the cathode 
 (as expressed by Faraday's Law) is proportional to (1) the strength 
 
 15 
 
16 PRINCIPLES AND DEFINITIONS 
 
 of current flowing, (2) the duration of the current, and (3) the 
 chemical equivalent weights of the substances. 
 
 NOTE. Otherwise expressed, the quantity of metal or other 
 substance separated is proportional to the total quantity of 
 electricity passing and the electro-chemical equivalent of the 
 substance or substances concerned. The electro-chemical 
 equivalent of a metal is proportional to its atomic weight 
 divided by its valence. Faraday's Law is so exactly realized 
 in practice under favorable conditions that it is used as the 
 basis for the definition of the international ampere, one of the 
 fundamental electrical units. (See Passivity, Paragraph 15.) 
 
 4. Cause of Current Flow. The current flowing through the 
 electrolyte may be due (1) to an external electromotive force or 
 (2) to the difference of potential due to the use of electrodes of 
 different materials or to solutions of different concentrations. 
 
 NOTE. The first case is illustrated by electrolysis of 
 dilute sulphuric acid using two lead plates and an external 
 battery; the second by the electrolysis of the same solution 
 using a zinc and a copper plate, which touch each other 
 inside or outside the solution. The first occurs in charging 
 a storage battery; the second in the discharging of a primary 
 battery or a storage battery. 
 
 5. Electrolysis by Local Action. Instead of two plates of 
 different metals the same result may follow with one plate if it is 
 chemically impure or otherwise heterogeneous, when immersed 
 in an electrolyte. 
 
 NOTE. Such a plate excites local currents and a loss of 
 metal occurs at all the anode areas. This local action causes 
 impure zinc to dissolve rapidly in a solution which has no 
 action on pure zinc. 
 
 6. Anodic Corrosion is the term applied to the loss of metal by 
 electrolysis at the anode. 
 
 NOTE. When iron is anode the iron is carried into solu- 
 tion by the current, the first product being a salt of iron, the 
 nature of which depends upon the character of the electrolyte. 
 In dilute sulphuric acid, ferrous sulphate is formed ; in hydro- 
 chloric acid, ferrous chloride, etc. These first products of 
 electrolysis are frequently modified by secondary reactions. 
 
 7. Secondary Reactions are the chemical changes which occui 
 at or near the electrodes, by which the primary products of elec- 
 
PRINCIPLES AND DEFINITIONS 17 
 
 trolysis are converted into other chemical substances, and are 
 sometimes followed by other reactions. 
 
 NOTE. Ferrous hydroxide formed by the union of iron 
 with hydroxyl ions set free at the anode, is subsequently 
 converted into iron oxide due to the reactions with oxygen 
 dissolved in the electrolyte. When lead is cathode in an 
 alkali soil or solution, the alkali metal (such as sodium or 
 potassium) reacts with water at the cathode and forms 
 alkali hydroxide, setting hydrogen free. This hydroxide 
 may react with the lead chemically and form lead hydroxide 
 (especially after the current ceases), which in turn may com- 
 bine with carbon dioxide, forming lead carbonate. 
 
 8. Calhodic Corrosion is the term applied to the corrosion 
 due to the secondary reactions of the cathodic products of elec- 
 trolysis, as described in the preceding paragraph. The metal of 
 the cathode is not removed directly by the electric current but 
 may be dissolved by a secondary action of alkali produced by 
 the current. 
 
 NOTE. The anodic corrosion is more common and more 
 serious; cathodic corrosion, however, sometimes occurs on 
 lead and other metals that are soluble in alkali. Cathodic 
 corrosion never occurs in the case of iron. 
 
 B. ELECTROLYSIS OF UNDERGROUND STRUCTURES. 
 
 9. General. As used in this report, the term "electrolysis" 
 embraces the entire process of accelerated corrosion of under- 
 ground metallic structures due to stray current. In the electrol- 
 ysis of gas arid water pipes, cable sheaths, and other underground 
 metallic structures, and the rails of electric railways, the moisture 
 of the soil with its dissolved acids, salts, and alkalis is the electro- 
 lyte, and the metal pipes, cable sheaths and rails are the electrodes. 
 
 NOTE. Wherever the current flows away from the pipes 
 they serve as anodes and the metal is corroded. Metal or 
 gas or alkali, according to the nature of the soil, will be set 
 free at the cathode. . 
 
 10. Self Corrosion is the term applied when a pipe or other mass 
 of impure or heterogeneous metal buried in the soil is corroded 
 due to electrolysis by local action. 
 
 NOTE. This is called "self corrosion" because the electric 
 current originates on the metal itself, without any external 
 agency to cause the current to flow. Self corrosion may also 
 be due to direct chemical action. 
 
 11. Acceleration of Local or Self Corrosion. Self corrosion is 
 accelerated by the presence in the soil water of acid or salts which 
 
18 PRINCIPLES AND DEFINITIONS 
 
 lower its resistance as an electrolyte, and also by cinders, coke or 
 some other conducting particles of different electric potential 
 which augment the local electric currents. In the latter case the 
 metal need not be heterogeneous. 
 
 NOTE. A pipe may be destroyed in a relatively short time 
 by self corrosion or local action if buried in wet cinders or in 
 certain soils. 
 
 12. Stray Current is that current which has leaked from the 
 return circuit of an electric railway system and flows through the 
 earth and metallic structures embedded therein. 
 
 13. Anodic and Self Corrosion. Anodic corrosion due to stray 
 currents and self corrosion due to local action may occur simul- 
 taneously, and the former may accelerate the latter. 
 
 NOTE. Hence the corrosion due to a given current plus 
 the increased self corrosion induced by that current may give 
 a greater total corrosion than called for by Faraday's Law. 
 This explains how the coefficient of corrosion may exceed 
 unity. 
 
 14. Coefficient of Corrosion. The coefficient of electrolytic 
 corrosion (sometimes called corrosion efficiency) is the quotient 
 of the total loss of metal due to anodic corrosion (after deducting 
 the amount of self corrosion if any) divided by the theoretical 
 loss of metal, as calculated by Faraday's Law, on the assumption 
 that the corrosion of the anode is the only reaction involved. 
 
 NOTE. In practice it is found that the coefficient of 
 corrosion varies widely from unity, being sometimes as low 
 as 0.2 and sometimes even above 1.5, but commonly between 
 0.5 and 1,1. 
 
 15. Passivity is the name given to the phenomenon in which a 
 current flows through an electrolyte without producing the full 
 amount of anodic corrosion which would occur under normal 
 conditions. 
 
 NOTE. This restricted definition of passivity has regard 
 only to its effect in electrolysis. Many conditions affect 
 the degree of passivity attained, an initial large current den- 
 sity being favorable to it. Plunging iron into fuming nitric 
 acid renders it temporarily passive. A satisfactory explana- 
 tion of passivity has not been given. 
 
 16. Polarization Voltage (sometimes called polarization poten- 
 tial) is the temporary change in the difference o'f potential "between 
 an electrode and the electrolyte in contact with it due to the 
 
PRINCIPLES AND DEFINITIONS 19 
 
 passage of a current to or from the electrode. This change in 
 potential difference is due to the change in the conditions of the 
 surface of the electrode or change in the concentration of the 
 electrolyte (or both), and under some conditions is approximately 
 proportional to the current flowing, but in many cases is not so 
 proportional. The magnitude of the polarization voltage also 
 depends on the material of the electrode, the nature of the electro- 
 lyte, and the direction of the current. 
 
 17. Alternating or Frequently Reversing Direct Currents. If 
 
 alternating currents (or frequently reversing direct currents) flow 
 through the soil between pipes or other underground metallic 
 structures, the metal removed during the half cycles when a pipe 
 is anode may be in part replaced when it is cathode. Hence, the 
 total loss of metal on a given pipe may be less than is indicated by 
 computing the loss on the basis of the positive part of the cycle 
 only, and in the case of alternating current at commercial fre- 
 quency may be less than 1% of such computed values. 
 
 NOTE. In slow reversals of current the recovery effect is 
 less, but the loss will be less than with direct current con- 
 tinuously in the same direction (excepting possibly where 
 the phenomenon of passivity may affect the result). 
 
 18. Action on Underground Metallic Structures. Faraday's 
 Law applies to electrolysis of metallic structures in soil as else- 
 where, the total chemical action being proportional to the average 
 current strength and the time the current flows and to the elec- 
 trochemical equivalent of the metal of other substances concerned. 
 Although local action and passivity affect the loss of metal and 
 so apparently modify Faraday's Law, it is still true that the 
 total chemical action resulting from the current flow is proportional 
 to the total current when local currents are included. 
 
 NOTE. Sometimes this chemical action is concerned only 
 with corroding the anode; sometimes it is concerned with 
 breaking up the electrolyte, as when the anode is a noble 
 metal or in the passive state (as iron and lead sometimes are) : 
 sometimes both these effects occur. 
 
 The theoretical loss of iron per year per ampere is about 
 twenty pounds and of lead is 3.7 times this amount or about 
 seventy-four pounds. The loss in volume of lead is 2.4 
 to 2.6 times that of iron. The greater loss in lead is due to 
 the higher electrochemical equivalent of that metal. 
 
 19. Electrolysis Mitigation. The two primary features of 
 electrolysis mitigation are (1) the reduction of the flow of current 
 
20 PRINCIPLES AND DEFINITIONS 
 
 through the earth and the metallic structures buried in the earth, 
 (2) the reduction of the anode areas of such structures to a mini- 
 mum, where the current is not substantially eliminated in order 
 to reduce the area of destructive corrosion as far as possible. 
 
 NOTE. The current in the underground metallic structures 
 will be decreased, other conditions remaining the same, by 
 (1) increasing the conductance of the return circuit, (2) 
 increasing the resistance of the leakage path to earth, (3) 
 increasing the resistance between the earth and the under- 
 ground metallic structures, (4) increasing the resistance of 
 the underground metallic structures. 
 
 The anode areas of the underground metallic structures 
 will be decreased, other conditions remaining the same, by 
 providing suitably placed metallic conductors for leading 
 the current out of the underground structures so that the 
 flow of the current directly to the earth shall be minimized. 
 This will change a portion of the anode area to cathode. 
 
 20. Electrolysis Survey. An electrolysis survey is the opera- 
 tion of determining by means of proper measurements all relevant 
 facts pertaining to electrolysis conditions, such as the voltage 
 drop in the grounded railway return; the location and extent 
 of the areas in which the metallic structures are in danger from 
 stray currents; the condition of the structures and adjacent soil 
 in the danger areas, and the extent of any damage that may have 
 occurred; the seriousness of electrolytic action in progress and the 
 source of the stray current producing the damage, its course and 
 magnitude and the conditions in neighboring structures tending 
 to produce electrolysis. If will generally be found desirable to 
 make some preliminary tests for the purpose of indicating the 
 lines along which the complete survey should be made. 
 
 21. Overall Potential Measurements. Overall potential meas- 
 urements are measurements which are made to determine the 
 difference in electric potential between points in the tracks at 
 the feed limits of the station and the point in the tracks which is 
 lowest in potential, and are obtained by means of pressure wires 
 and indicating or recording voltmeters. This is most commonly 
 applied to measurements of voltage between the point of lowest 
 potential in the grounded portion of a railway return system and 
 the points of approximately highest potential on its various 
 branches. 
 
 22. Potential Gradient. A potential gradient is the voltage 
 drop per unit of length between two points on a single conductor 
 
PRINCIPLES AND DEFINITIONS 21 
 
 or in the earth, and is usually expressed in volts per thousand 
 feet. 
 
 23. Potential Difference. In electrolysis work the term 
 "potential difference" usually means the difference in potential 
 which exists between nearby points on separate systems of con- 
 ductors, or between conductors and the earth, e.g., between pipes 
 and rails, lead sheaths and rails, lead sheaths and earth, etc. 
 
 24. Arithmetical Average. The arithmetical average value of 
 a current or potential is the average value of all the instantaneous 
 values of the same polarity. 
 
 25. Algebraic Average. The algebraic average value of a 
 current or potential is the algebraic sum of all the instantaneous 
 values, divided by the number of such values. 
 
 26. Positive and Negative Areas. Positive areas are those 
 areas where the current is in general leaving the pipes or other 
 underground metallic structures for the earth. Such areas are 
 often called danger areas. 
 
 Negative areas are those areas where the current is in general 
 flowing to the pipes or other underground metallic structures. 
 
 NOTE. As the current often flows from one underground 
 metallic structure to another, it is evident that within a 
 positive area there are local negative areas and vice versa. 
 Hence the terms are applied somewhat loosely, and according 
 to which condition predominates. 
 
 Besides the positive and negative areas there are areas of 
 more or less indefinite extent in which the current flow 
 between metallic underground structures and earth normally 
 reverses between positive and negative values. These areas 
 are called neutral areas or neutral zones. 
 
 27. Drainage System. A drainage system is one in which 
 wires or cables are run from a negative return circuit of an electric 
 railway and attached to the underground pipes, cable sheaths or 
 other underground metallic structures which tend to become 
 positive to earth, so as to conduct current from such structures 
 to the power station, thereby tending to reduce the flow of current 
 from such 'structures to earth. 
 
 NOTE. Three kinds of drainage systems may be distinguished : 
 (1) where direct ties with wires or cables are made between 
 underground metallic structures and tracks, (2) where un- 
 insulated negative feeders are run from the negative bus to 
 underground metallic structures, (3) where separate insulated 
 
22 PRINCIPLES AND DEFINITIONS 
 
 negative feeders are run from the negative bus to underground 
 metallic structures, or a main feeder with taps to such 
 structures. 
 
 28. Uninsulated Track Feeder System. An uninsulated track 
 feeder system is one in which the return feeders are electrically 
 in parallel with the tracks. Under such circumstances the cables 
 may be operating very inefficiently as current conductors and as 
 a means of reducing track voltage drop, particularly where 
 voltage drops in the grounded portion of the return are maintained 
 at the low values usually required for good electrolysis conditions. 
 (See Chapter 2, Reinforcement of Rail Conductivity.) 
 
 29. Insulated Negative Feeder System. An insulated negative 
 feeder system, sometimes called an insulated return feeder sysem, 
 or insulated track feeder system, is one in which insulated wires 
 or cables are run from the insulated negative bus in a railway 
 power station and attached at such places to the rails of the track 
 as to take current from the track and conduct it to the station 
 in such a manner as to reduce the potential gradients in the 
 tracks and the differences of potential between underground 
 metallic structures and rails, thereby reducing the flow of current 
 in underground metallic structures. (See Chapter 2, Insulated 
 Negative Feeder System.) 
 
 NOTE. The insulated negative feeders may run separately 
 from the negative bus to various points in the track network, 
 or a smaller number of cables may be used with suitable 
 resistance taps made to tracks at various places. 
 
 With this system the drop of potential in the track feeders 
 is independent of the drop of potential in the tracks. 
 
CHAPTER 2 
 
 DESIGN, CONSTRUCTION, OPERATION AND 
 MAINTENANCE 
 
 The practical electrolysis problem is due to stray current from 
 electric railways. Instances of stray direct currents from other 
 sources sometimes occur, but such cases are not specifically 
 considered in this report. 
 
 Currents straying to earth from electric railway tracks frequently 
 find their way to water and gas pipes, telephone and power cables, 
 and other underground structures. When this current leaves 
 these structures through earth, corrosion results. Thus not only 
 are the structures of many different companies subject to injury, 
 but by reason of the different public services dependent on such 
 structures, the public as a whole has a direct interest in this type 
 of electrical interference. The problem, therefore, is one which is 
 preeminently adapted to cooperative treatment. 
 
 In many cities it has been found advantageous to form joint 
 committees, composed of technical representatives of the several 
 utilities concerned, to investigate the local electrolysis situation 
 and determine by agreement a course of procedure to be followed. 
 Such committees should attack the problem in an open and fair- 
 minded manner with the object of effecting, in the most economical 
 way, mitigation of all the troubles resulting from the presence 
 of stray currents in the earth, including corrosion, fire and explo- 
 sion hazards, heating of power cables, and operating losses and 
 difficulties. To this end, they should be composed of men, or 
 have men associated with them, who are trained in the technique 
 of electrolysis. Active committees of the kind described are now 
 existent in Chicago, Kansas City, Omaha, St. Paul, New Haven, 
 Milwaukee, and Syracuse. The principle of cooperation has 
 been recognized by the Railroad Commission of Wisconsin in an 
 order authorizing an Electrolysis Committee in the City of Mil- 
 waukee. Such committees act as clearing houses of information 
 and keep all the interested companies informed as to changes in 
 their systems which may affect the electrolysis situation. Under 
 the direction of such a committee joint electrolysis surveys may 
 be conducted and unified methods of mitigation installed and 
 maintained. 
 
 The magnitude of stray currents is determined by the design, 
 construction, maintenance, and operation of the railway system. 
 
 23 
 
24 DESIGN, CONSTRUCTION, OPERATION, ETC. 
 
 In general, the same factors that determine the amount of stray 
 currents are those that have a direct bearing on the economy of 
 railway operation. A good example is that of an insufficient 
 number of substations, which results both in large stray currents 
 and poor railway economy. Similar results follow from defective 
 bonding, rails of inadequate size, or failure to interconnect 
 tracks. For this reason, it is believed that many existing railway 
 systems can be modified in such a way as to increase their own 
 economy of operation, while at the same time securing important 
 reduction in stray current. Measures of this character, which 
 are essential to the most economic operation of the railway, should 
 be regarded as a prerequisite of the application, either to the 
 railway or to the affected structures, of measures specifically 
 for electrolysis mitigation. 
 
 Prior to the consideration of measures of electrolysis mitiga- 
 tion, the following features should be given due attention : 
 
 1. Measures Tending Both to Railway Economy and the Reduc- 
 tion of Stray Current. 
 
 (a) The return system, including track bonding, should be 
 put in proper condition. 
 
 (b) The number of substations should be made a maximum 
 consistent with railway economy. 
 
 2. Measures Employed Solely for Electrolysis Prevention. 
 Where necessary to effect a still further reduction in electrolysis 
 
 below that provided by the most economic railway system one 
 or more of the following measures should be taken : 
 
 (a) Applicable to Railways. (1) Additional substations, (2) 
 Insulated negative feeders, (3) A modified system of power dis- 
 tribution such as a three-wire system. 
 
 (b) Applicable to Affected Structures. (1) Insulating joints in 
 pipes and cables, (2) Insulating coverings for pipes. 
 
 (c) Interconnection of Affected Structures and Railway Return 
 Circuit. (1) Electrical drainage of cable sheaths, (2) Electrical 
 drainage of pipes. 
 
DESIGN, CONSTRUCTION, OPERATION, ETC. - 25 
 
 I. RAILWAYS 
 
 A. FEATURES WHICH AFFECT ELECTROLYSIS 
 CONDITIONS 
 
 1. Track Construction and Bonding. 
 
 (a) Importance of Rail Circuit. Stray current is increased by A [ 
 insufficient rail weights and imperfectly bonded track joints, p 
 While the major portion of the current of a grounded return 
 railway generally returns through the tracks and return feeders 
 
 to the power station, a portion finds a parallel path through the 
 earth and its buried metallic structures. As the current flowing 
 in each path is inversely proportional to the resistance of that 
 path, it is of prime importance to make the resistance of the track 
 
 circuit as low as possible by the use of rails of adequate weight . 
 
 and proper bonding. 
 
 (b) Rail Bond Resistance and Tests. The contact resistance 
 of the bond terminal connection to the rail may be a considerable 
 part of the resistance of the joint if the bond is not properly 
 installed and maintained and it is therefore essential in selecting 
 the type of bond to be used, that special consideration be given 
 this feature. 
 
 It is the usual practice to measure the resistance of the bonded 
 joint including three feet of rail in terms of a length of continuous 
 rail. The equivalent length of a properly bonded joint including 
 three feet of rail, varies from 3 to 6 feet, depending upon the size 
 of the rail, and the type, length and cross sectional area of the 
 bonds. On some electrified steam roads it is the practice to bond 
 so that the joint alone will have an equivalent resistance of 20 || 
 inches of continuous rail and to rebond when this resistance " 
 increases to 42 inches. On street railway systems bonding to an 
 equivalent length of 3 to 6 feet is common practice where short 
 .bonds are used, rebonding when the joint resistance including 
 three feet of rail increases to that of 10 feet of rail. A single No. 
 0000 long bond, installed around the splice plates will have with 
 three feet of rail, a resistance equivalent to from 8 to 15 feet of 
 continuous rail, depending upon the size of the rail. 
 
 Practice varies widely as to the frequency of testing rail bonds 
 but most railway companies make complete tests of all bonds at 
 least once each year and more frequent tests on tracks subject to 
 excessive traffic or deterioration. Good practice would require 
 annual tests of all bonds, and semi-annual on tracks in which 
 the bond failures exceed five per cent annually. 
 
26 DESIGN, CONSTRUCTION, OPERATION, ETC. 
 
 (c) Types of Bonds. Bonds may be classified according to the 
 method of fastening them to the rails as follows : 
 
 (1) Soldered. 
 
 (2) Brazed or Welded. 
 
 Resistance Weld. 
 Electric Arc Weld. 
 Oxy-Acetylene Weld. 
 
 (3) Pin Expanded. 
 
 (4) Compressed Terminal. 
 
 Solid Single Terminal. 
 Single or Multiple Stud. 
 
 There is a further distinction between exposed and concealed 
 bonds, the latter being used where the prevention of theft is a 
 serious consideration, in which case the bonds are installed under- 
 neath the splice plates. 
 
 Local conditions will largely determine the type of bonding 
 to be used. Consideration should be given to the economy of 
 construction, maintenance, costs, facilities for using bonding 
 equipment, tools, etc. In recent years there has been a marked 
 tendency toward the more general use of all types of welded bonds 
 with almost complete abandonment of soldered bonds and those 
 mechanically applied to the head of the rail. Pin-terminal and 
 compressed-terminal bonds are still extensively used for applica- 
 tion to the web of the rail but even here the welded type is finding 
 favor with many companies. One reason for the increasing use 
 of oxy-acetylene and electric alloy welded bonds is to be found 
 in the lighter, cheaper, and more portable tools for their applica- 
 tion, some of the newer methods and apparatus which have been 
 developed for this class of work being far superior to those formerly 
 employed. 
 
 Soldered Bonds are applied to the head, base or web of the 
 rail by means of solder, a blow torch being used to heat the rail" 
 to a soldering temperature. The difficulty of securing a permanent 
 and low resistance contact has caused practically all railway 
 companies to abandon this type of bond. 
 
 Brazed or Welded Bonds are applied either by the use of the 
 heating effect of an electric current or arc or an oxy-acetylene 
 gas flame. 
 
 . The Resistance Weld of bond to rail is accomplished by clamping 
 a carbon block against the head of the bond and heating this 
 block to a high temperature by the passage of a large electric 
 current or by drawing an arc on the face of the block. 
 
DESIGN, CONSTRUCTION, OPERATION, ETC, 27 
 
 In the Electric Arc process the arc is drawn directly on the rail 
 and bond terminal. In both the resistance and arc methods of 
 welding or brazing the rail and bond terminals are brought to a 
 welding or brazing heat and united in a solid mass by filling in 
 metal, thus forming a mechanical and electrical union. The 
 filling in metal may be a copper or iron wire used as an electrode. 
 When the bond terminal is steel, the latter metal is used. Several 
 methods, differing somewhat in the equipment used and the 
 methods of applying the heat to the bond and rail, are in use, and 
 the selection of the most suitable of these will depend upon a 
 number of factors and often upon local conditions. 
 
 The Oxy-Acetylene process is similar to arc welding except that 
 the heating is accomplished by means of an oxy-acetylene gas 
 flame from a blow torch. 
 
 These methods give a connection of low resistance and short t\ 
 bonds can be applied to the head of the rail without much danger \ \ 
 of theft due to the small amount of copper involved and the 
 tenacious contact between bond and rail. 
 
 Pin Expanded Terminal Bonds have a hole in each terminal 
 through which a tapered drift pin is driven to expand it into 
 a hole drilled in the web of the rail after which a pin, slightly 
 larger than the drift pin, is driven into the hole and left there 
 to prevent contraction. This type of bond requires great care 
 and accuracy in manufacture and in installation, but when properly 
 installed makes a very efficient and satisfactory construction. 
 The essential features are a carefully and accurately milled termi- 
 nal and a perfectly clean, circular-drilled hole, reamed to proper 
 diameter, in the rail. Care should be used to brighten the terminal 
 with emery paper just before installing and to avoid contact with 
 the fingers which will cause corrosion between the terminal and 
 the rail. Holes should be drilled dry and bonding should not be 
 done except in fair weather so there will be no moisture to induce 
 corrosion. This type of bond is usually applied to the web of the 
 rail. As it requires only small portable tools it has been found 
 to be particularly well adapted to main line tracks under operating 
 conditions. 
 
 Compressed Terminal Bonds are of two kinds, one being a single 
 solid terminal bond applied to the web of the rail in a manner 
 similar to the Pin Expanded Terminal bonds described above 
 except that contact with the rail is secured by means of a heavy 
 screw or hydraulic compressor applied to each end of the terminal, 
 causing it to compress longitudinally and expand laterally, bringing 
 
28 DESIGN, CONSTRUCTION, OPERATION, ETC. 
 
 the copper into firm contact with the steel. The screw compressors 
 used for compressed terminal bonds are objectionable where fast 
 traffic is maintained on the tracks as they clamp over the head of 
 the rail, making a dangerous condition due to the possibility of 
 causing derailment. The other is a single or multiple stud terminal 
 bond applied to the head of the rail, the terminal studs being set 
 in holes and expanded into contact by hammer blows. This 
 type of bond has been largely superseded by the modern types of 
 brazed- and welded head bonds. 
 
 (d) Welded Rail Joints. The difficulties and uncertainties 
 attending the proper maintenance of rail joints and bonds have 
 been eliminated to a large degree by the successful use of several 
 modern types of welded joints, such as electric resistance and arc 
 welding, cast welding, and thermit welding. The welded joint 
 in one form or another has been adopted as a standard of con- 
 struction in nearly every large city in the United States. Most 
 types of welded joints have a conductivity equal to or greater 
 than the continuous rail and are less subject to failure than any 
 form of rail bond. They must be considered, therefore as a most 
 important factor in the reduction of stray current. 
 
 Electric Rail Welding is performed by clamping heavy iron bars 
 to the web of the rail and bringing the bars and the adjacent rail 
 to a white heat by means of an electric current. The process 
 requires a heavy and expensive plant and is usually carried out by 
 contract on a comparatively large scale. For this reason it is not 
 well suited to installations on small systems. It is well adapted 
 to the reclaiming of old track as well as for new work and has 
 been applied on open T-rail construction where expansion joints 
 are installed at intervals to provide for expansion and contraction. 
 
 Arc Welding. There are several forms of arc welding where 
 the splice bars are welded to the rail at a number of points by the 
 use of an electric arc. Electric arc welding may be done under 
 traffic conditions and is more extensively used in maintenance work 
 than other methods. 
 
 Cast Welding is accomplished by setting a mould around the rail 
 joint and pouring molten iron from a crucible around the joint. 
 This process requires transporting a portable cupola along the 
 street adjacent to the work. On account of the improvement in 
 similar types of joints with more portable equipment, this method 
 is not now used as much as formerly. 
 
 The Thermit process is a modification of the cast weld, the iron 
 being liberated at white heat from a mixture of iron oxide and 
 
DESIGN, CONSTRUCTION, OPERATION, ETC. 29 
 
 aluminum, which is ignited in a crucible. Cast welding is used 
 chiefly on new construction and cannot be done under traffic. 
 The renewal of a cast weld joint requires cutting in a short length 
 of new rail which adds another joint to the track. 
 
 (e) Cross-bonding. The important objects of cross-bonding 
 are to equalize the current flow between the rails, thus reducing the 
 voltage drop and also to insure continuity of the return circuit in 
 case of a broken length of rail or a broken bond in any rail. It is 
 good practice to place cross-bonds at intervals of 1,000 to 2,000 feet 
 on suburban railways and not to exceed 500 feet on urban rail- 
 ways. Cross-bonding between parallel tracks is in some cases 
 installed with the same frequency as between .the rails of the 
 single track; in other cases at less frequent intervals. Some 
 companies make a practice of installing cross-bonds under each 
 feeder tap to the trolley wire or at every fourth or fifth span wire, 
 thus enabling them to conveniently preserve a record of their 
 locations. In cases where the track has been carefully insulated 
 cross-bonds should preferably be rubber insulated so as to in- 
 crease their electrical resistance to earth, and where subject to 
 damage from track tools and to other mechanical injury the insu- 
 lation should be protected by circular loom or conduit. 
 
 The common practice of electrified steam railroads is to use 
 cross-bonds with a conductance equal to one track rail, or of 
 about 1,000,000 circular mils cross-section. Street and inter- 
 urban railways employ bonds having a cross-section of from 200,000 
 to 500,000 circular mils. 
 
 (f) Special Track Work Bonding. It is good practice to pro- 
 vide jumpers at switches, frogs and at other special track work 
 to insure that the electrical continuity of the bonded rail will be 
 maintained. This is usually accomplished by jumpers extending 
 around the special work, and in such cases the frogs are bonded 
 into the track system, or where practicable the special work is 
 bonded as other track rails. The size of the jumper cables to be 
 used will depend upon the nature of the traffic. On tracks bearing 
 heavy traffic a separate cable is usually provided for each rail, 
 while for light traffic a single jumper connecting to all rails on both 
 sides of the special work is sometimes used. In all cases the 
 jumpers should be proportioned to the current carried in the 
 track and in no case less than a No. 0000 for one track. 
 
 In cases where the track has been carefully insulated the best 
 practice provides for the use of insulated cables for jumpers, 
 except in dry locations, as for instance, on bridges or on other 
 
30 DESIGN, CONSTRUCTION, OPERATION, ETC. 
 
 elevated structures where the ties are not in contact with earth 
 or ballast. The electrical leakage from one bare track juniper to 
 damp earth has been known to offset the effect of many miles of 
 most careful track insulation. Under such conditions, if positive 
 to the earth, the bond is gradually destroyed by electrolysis. 
 
 (g) Bonding Tracks with Signal Systems. In determining the 
 location of cross-bonds and jumpers in connection with alternating 
 current track signal circuits, a departure from ideal spacing 
 becomes necessary, owing to the fact that cross-bonds are per- 
 missible only at the reactance bonds. The signal reactance 
 bonds are located between the signal block sections, and these 
 sections are more or less fixed for train operating conditions. 
 The method used where tracks carry heavy currents is to cross- 
 bond at all signal reactance bonds and install additional cross- 
 bonds with reactance bonds at intermediate locations to obtain 
 the most satisfactory resistance conditions in the sections fixed 
 by the signal system. 
 
 (h) Conductivity and Composition of Rails. The conductivity 
 of the track rails used by several interurban and electrified steam 
 railroads has been found to be equivalent to about Jfi that of 
 copper, and this figure generally holds approximately true for 
 girder types of rails, except when alloy steel is used, in which case 
 higher resistivities are found. The track rails are specified for 
 their mechanical qualities, and where these interfere with the 
 electrical requirements, it is customary to give the mechanical 
 qualities preference. The composition of rails for heavy service 
 used by one of the large electrified steam railroads, in percentage, 
 is as follows : 
 
 Carbon 0.62 to 0.75 
 
 Manganese 0.70 to 1.00 
 
 Silicon 0.10 to 0.20 
 
 Phosphorous Not to exceed . 04 
 
 The American Railway Engineering Association has adopted 
 the following composition for heavy rails : 
 
 Class A Rails Class B Rails 
 
 Carbon 0.60 to 0.75 0.70 to 0.85 
 
 Manganese. 0.60 to 0.90 0.60 to 0.90 
 
 Silicon Not more than 0.20 Not more than 0.20 
 
 Phosphorous Not more than 0.04 Not more than 0.04 
 
DESIGN, CONSTRUCTION, OPERATION, ETC. 31 
 
 2. Track Insulation. 
 
 (a) Degrees of Insulation. Under this sub-heading have been 
 considered, (1) Substantial Insulation, in which the type of con- 
 struction largely prevents the escape of stray current, and (2) 
 Partial Insulation, which comprises using such means as are avail- 
 able to insulate from the earth the running rails of ordinary street 
 railways insofar as practicable. 
 
 Substantial Insulation. Interurban and electrified steam roads 
 generally require the rail to be supported on wooden ties set in 
 well drained broken stone or gravel ballast. Such construction 
 affords a very high resistance between the tracks and earth and 
 reduces the danger of electrolysis to a minimum. 
 
 With 10 volts between rail and ground the leakage in some 
 instances is found to be as low as 0.00016 amperes per rail per tie 
 under dry weather conditions, increasing to 0.0055 amperes when 
 wet. On double track with ties spaced 2 feet apart these values 
 represent 0.32 and 11.0 amperes, respectively, per 1,000 feet, or 31 
 and 0.91 ohms respectively for 1,000 feet. On steel structures 
 where the ties are only partially in contact with the ground and 
 cannot become waterlogged, this leakage is even less. The 
 substantial insulation of a ballasted roadbed has, in some installa- 
 tions, been rendered ineffective by bare negative cables in damp 
 earth or by metallic connections between the tracks and steel 
 supporting structures. Conditions are found to be very favorable 
 for rail insulation where the tracks are in subways or under cover 
 protected from the weather, permitting the ballast and ties to 
 become permanently dry. 
 
 Partial Insulation. Tracks placed in city streets where rails 
 are depressed to the surface of the ground and have only their 
 upper surface exposed can be but partially insulated. The 
 character of the material in immediate contact with the rails 
 has a large influence on the resistance to ground, but it has been 
 repeatedly demonstrated that coating the rails with an insulating 
 material is not advisable, and the best plan is to provide a roadbed, 
 which, taken as a whole, is of an insulating character. The use 
 of well drained broken stone or gravel ballast results not only 
 in a good roadbed, but also affords a much higher resistance to 
 the escape of stray current than does a roadbed of concrete. It 
 is desirable to keep vegetation down and otherwise keep the 
 ballast dry and prevent foreign material from washing into it. 
 Salt, which is frequently used to prevent freezing at switches and 
 
32 DESIGN, CONSTRUCTION, OPERATION, ETC. 
 
 frogs, greatly increases the conductivity of the roadbed and 
 thereby facilitates the escape of stray current. 
 
 Electric railways have experienced some damage due to the 
 corrosion of the base of the rail or of elevated structures connected 
 to the rails in districts where the stray current leaves the structure 
 for the earth. Cases are on record where this corrosion is serious 
 and where steps have been taken to reduce the damage to elevated 
 structures by insulating the rail from the steel structure. Any 
 measure which tends to insulate the track from the soil or any 
 mitigative system which tends to reduce stray current will tend 
 to retard the electrolytic corrosion of the base of the rails and 
 other grounded steel structures. 
 
 (b) Leakage to be Expected. Under conditions of substantial 
 insulation and where the roadbed is of open construction the 
 leakage varies widely depending upon the character of the ballast 
 and whether it is wet or dry. In dry weather the resistance may 
 be from 10 to 15 ohms or even more per 1,000 feet of single track. 
 In wet weather this may drop to 3 to 5 ohms. If ties are treated 
 with a 3 to 1 mixture of gas oil and creosote, the resistance may be 
 double the above values whereas with ties treated with zinc 
 chloride or other chemical salts the resistance may be one-half 
 of these values. 
 
 The leakage where tracks are only partially insulated will not 
 only be much greater than where they are substantially insulated 
 but will vary over a much wider range. This is because the type 
 of roadbed, character of soil, and drainage conditions vary greatly. 
 It is known that well drained crushed stone ballast with a Tarvia 
 finish will have a resistance from 2 ohms to 5 ohms per 1 ,000 feet 
 of single track. On the other hand the resistance of roadbeds 
 with solid concrete ballast in contact with the rails and also earth 
 roadbeds, in which the ties are embedded and therefore in a 
 more or less moist condition, are much lower and may be only 
 from 0.5 to 1.5 ohms for 1,000 feet of single track. 
 
 3. Reinforcement of RaiL Conductivity. 
 
 Early track construction practice in this country often included 
 bare wire laid between the rails and connected to each bond. 
 Sometimes one such wire was used for each rail, sometimes one 
 for each track, and sometimes one served for a double track. 
 The wires varied from No. 4 to No. 1, and were either of copper 
 or galvanized iron. Their conductivity was small and they were 
 subject to electrolytic corrosion and mechanical injury. This 
 
DESIGN, CONSTRUCTION, OPERATION, ETC. 33 
 
 construction has practically gone out of use. It is, however, 
 common to find the rails in the vicinity of supply stations supple- 
 mented by large conductors connected in parallel with the rails. 
 This is not infrequently accomplished by the use of bare copper 
 wire or cable buried between rails, and hence in full contact with 
 the earth. Old rails, bolted and bonded together and buried 
 beneath or beside the track, have also been used in some cases. 
 Such buried conductors increase the leakage from the tracks and 
 should be avoided. 
 
 Supplementary conductors in parallel with the track and 
 connected to it at frequent intervals tend greatly to insure the 
 continuity of the return circuit, where the track bonds cannot 
 be well maintained. Where copper cables are so used the occa- 
 sional failure of bonds does not materially affect the track drop 
 and their use may be justified where tracks are laid on filled or 
 spongy ground or where the proper maintenance is unusually 
 difficult. 
 
 Buried bare conductors, however, increase the contact area 
 between the return circuit and the earth, and the tendency to 
 augment stray currents thus caused offsets to a greater or less 
 extent the benefits attained by the reduction of drop. 
 
 Copper installed in this manner is in parallel with the rails, 
 and therefore has the same drop as exists in the rails. As track 
 gradients rarely exceed two or three volts per thousand feet, 
 this would mean that the drop on such cables would not exceed 
 two or three volts per thousand feet, which corresponds to a current 
 density of about 190 or 280 amperes respectively, per 1,000,000 
 circular mils. It will be seen that these densities are so low that 
 such use of the copper is very uneconomical and for this reason 
 this method of reinforcement of the rail conductivity should not 
 ordinarily be used. 
 
 Conductors are regarded as being in parallel with the rails 
 when both ends are connected to the tracks or when one end is 
 connected to the track and the other to a station busbar which is 
 connected directly to the rail by a conductor of negligible resist- 
 ance. The use of such conductors should not be confused with 
 the insulated negative feeder system. 
 
 4. Power Supply. 
 
 Among the various features of railway construction which tend 
 to reduce stray current none has made more rapid advancement 
 during recent years than the development of multiple feeding 
 
34 DESIGN, CONSTRUCTION, OPERATION, ETC. 
 
 points, principally from use of additional substations supplying 
 the railway systems. Increasing the number of .substations will 
 reduce the feeding distances and effect a saving in distribution 
 copper and in line and return losses, and will also reduce the 
 amount of current to be returned to any one point. The general 
 effect is to reduce the track voltage drops, thereby reducing the 
 amount of current which will stray from the rails to subsurface 
 metallic structures. 
 
 If The ordinary street railway system employs direct current 
 ( at from 550 to 750 volts. Some interurban lines operate at 1200 
 volts direct current and voltages as high as 3000 volts are used 
 on the electrified sections of some railroads. 
 
 (a) High Voltage D. C. Railways. Railway systems of higher 
 potentials than the ordinary 550-750 volt systems may cause 
 more or may cause less stray currents than the latter, depending 
 upon conditions. With the same -spacing of substations the 
 current will be less in proportion as the voltage is greater. Usu- 
 ally, however, advantage is taken of the higher potential to locate 
 the power supply stations farther apart, maintaining approxi- 
 mately the same current density in the tracks with the usual 
 
 ft potential gradient. This, of course, results in increased overall 
 jj voltage drops which tend to increase the stray currents. 
 
 In making comparison of high voltage and low voltage systems 
 from an electrolysis standpoint, the difference in conditions must 
 be taken into account. As a rule high voltage direct current is 
 used principally on roads having a private right-of-way with rails 
 on ties supported on well drained rock ballast. Moreover, the 
 major portion of such lines are located in country districts with 
 no buried metallic structures paralleling them, but in some cases 
 such lines pass through cities or towns, or at least enter their 
 suburbs, in which event suitable measures to prevent injury by 
 electrolysis should be taken. 
 
 (b) Source of Stray Currents. A single trolley electric railway 
 system with an adjacent buried pipe line is illustrated in Fig. 1, 
 in which the underground network of pipes is represented by a 
 pipe parallel to the tracks. At points remote from the power 
 supply station, the current which reaches the rails from the cars 
 will divide between the several possible paths, and the amount 
 flowing along any path will be inversely proportional to the 
 resistance of that path. A portion of the current, therefore, will 
 leave the rails at points remote from the station and pass through 
 the earth to the adjacent pipes, then flow along the pipes toward 
 
DESIGN, CONSTRUCTION, OPERATION, ETC. 
 
 35 
 
 K 
 
 \ 
 \ 
 \ 
 
 <0 
 
 i 
 
 <r 
 
 c 
 
 in 
 
 
 F 
 
 j> 
 a- 
 
 V) 
 
36 
 
 DESIGN, CONSTRUCTION, OPERATION, ETC. 
 
 the station, leaving the pipes near the station and returning 
 through the earth to the rails and thence to the station as in- 
 dicated by the arrows in Fig. 1 . The region near the station where 
 the pipes are positive to the surrounding earth, and where the 
 current leaves the pipes to return to the rails, is the region where 
 damage by electrolysis will occur, and is called the danger or posi- 
 tive area. 
 
 ial Gradiev 
 
 Dtsfance End of Line 
 
 Potential Profile of 
 Rai I vvay Ss tern 
 
 Fig. 2. 
 
 If the cars are uniformly distributed along the line, and if the 
 track is of uniform resistance throughout its length, the voltage 
 profile along the track will be as shown in Fig. 2. This curve is a 
 parabola with a vertical axis and with its apex at the end of the 
 line. The potential drop from the end of the line to any point 
 on the line is therefore proportional to the square of the distance 
 from the end of the line. The slope of this curve is a measure 
 of the potential gradient. If the resistance of the track is^known, 
 
DESIGN, CONSTRUCTION, OPERATION, ETC. 
 
 37 
 
 the potential gradient at any point serves as a measure of the 
 amount of current flowing in the rails at that point. 
 
 If there are no metallic connections between the rails and the 
 pipes, then the potential profile of the pipes will be something 
 like that indicated in Fig. 3. 
 
 In the regions remote from the supply station the pipes are 
 
 ion 
 
 Distance 
 
 End of Line 
 
 Potential Profile Showing Rails & Pipes 
 Wrfhout Connections Between Pipes and 
 Railway Return Circuit 
 
 Fig. 3. 
 
 seen to be negative to the rails and near* the station they are posi- 
 tive to the rails. Ordinarily the positive area extends from 30 
 to 40 per cent of the distance from the supply station to the end 
 of the line. At the neutral point where no potential difference 
 exists between the pipes and the earth the stray current in the 
 earth and underground structures is a maximum. 
 
 The amount of stray current is more nearly a function of the 
 
38 DESIGN, CONSTRUCTION, OPERATION, ETC. 
 
 overall voltage drop than of the potential gradient at any point. 
 While high potential gradients extending over a considerable 
 length of track will result in a high overall voltage with corres- 
 pondingly large stray currents, the existence of a high gradient 
 on a comparatively short section of track is of much less con- 
 sequence. The reduction of feeding distances and overall potentials 
 has such a marked influence on stray currents that a rather full 
 treatment of this subject is here given. 
 
 (c). Relation of Feeding Distance to Stray Currents and Overall 
 Voltages. The effects of the reduction of feeding distances on 
 stray currents and overall potential drops are illustrated in Figs. 
 4 and 5. The stray current curves are calculated from the 
 formulas found in Technologic Paper No. 63 of the Bureau of 
 Standards, entitled "Leakage Currents from Electric Railways." 
 They represent conditions on a typical line having the following 
 characteristics: Double track, 72-lb. rails; length of line, 20,000 
 feet; calculated resistance of the track, 0.004 ohm per 1,000 feet 
 (this figure allows for a 10 per cent increase in the resistance of 
 72 Ib. rails, due to the bonds; it corresponds approximately to 
 the resistance of 2.5 million circular mils of copper). The leakage 
 resistance is taken as 0.4 ohm for 1,000 feet, of double track which 
 is a fair average for city tracks in paved streets with a crushed 
 stone foundation. An average load of 40 amperes per 1,000 feet, 
 corresponding to a headway of 4 minutes each way, is considered 
 uniformly distributed along the line. The total average load is, 
 therefore, 800 amperes, corresponding to a station capacity of 
 1,000 kw., on the assumption that the peak load is double the 
 average load. 
 
 Calculations of stray current have been made for both the 
 insulated bus and the grounded bus conditions. This latter occurs 
 only when all of the stray current returns to the negative bus 
 without re-entering the track system, a condition which does not 
 ordinarily occur in practice. An approach to a grounded bus 
 would be a system where extensive pipe drainage existed with a 
 large portion of the current returning to the bus from the under- 
 ground piping and cable systems. Another condition which 
 simulates a grounded bus is often found where bare copper cables 
 which are used to connect the negative bus with the nearby rails 
 are permitted to come in contact with wet earth or are laid in a 
 stream or river bed. Railway stations generating direct current 
 are often located in low ground or on rivers where condensing 
 water is available and unless special precautions are taken to 
 
DESIGN, CONSTRUCTION, OPERATION, ETC. 
 
 39 
 
 insulate negative cables entering such stations they are likely 
 to pickup considerable current from the earth, thereby establishing 
 the condition of a semi-grounded bus. 
 
 Fig. 4 shows the total current returning to a single supply station 
 located at the end of the line. The stray current at any point is 
 also shown for the cases of the bus grounded and the bus not 
 grounded. By insulating the bus the maximum value of the stray 
 
40 
 
 DESIGN, CONSTRUCTION, OPERATION, ETC. 
 
 current is reduced from 417 amperes to 147 amperes and by putting 
 the supply station at the middle of the line instead of at the end 
 and thereby reducing the feeding distance to one-half, the maximum 
 
 value of the stray current with insulated bus is reduced from 147 
 amperes to about 24 amperes. 
 
 Fig. 5 shows the overall voltage curves for the same line fed 
 from the end, from the center, and also from two stations located 
 
DESIGN, CONSTRUCTION, OPERATION, ETC. 
 
 41 
 
 at one-fourth and three-fourths of the distance to the end of the 
 line respectively. Shortening the feeding distance to one-half 
 reduces the overall voltage to one-fourth of the original value and 
 cutting the feeding distance to one-fourth reduces the overall 
 voltage to one-sixteenth of the original value; or as previously 
 
 stated, the overall voltage varies as the square of the 
 feeding distance. The curves in Fig. 5 are based on theoretical 
 conditions with no stray current. The actual overall voltages 
 would be somewhat less because of part of the current being in the 
 earth. The dotted lines in Fig. 5 illustrate in a 'general way the 
 
42 DESIGN, CONSTRUCTION, OPERATION, ETC. 
 
 potential of the earth and pipes under the several conditions of 
 feeding and the shaded portions represent the areas where the 
 earth and pipes are positive to the rails 
 
 The effect of providing additional centers of power supply 
 can also be illustrated by the curves in Fig 6, which, while cal- 
 culated on the assumption of no stray current, illustrate in a 
 simple case, the effects which have been observed in practice. 
 
 The curve SAO represents the track voltage drop on a portion 
 of an electric railway system having a uniformly distributed load. 
 The curve SBF illustrates the condition of a substation located 
 at P, 33 per cent of the distance from Q to S, carrying 20 per cent 
 of the total load. In this curve the portion BF is identical with 
 AO. As the load is uniformly distributed, 33 per cent of the load 
 is on the portion of the line shown by PQ, and of this 33 per cent, 
 20 per cent is carried by the substation P. The remainder, or 
 13 per cent, is carried by the station S. The point B on the curve 
 SBF, therefore, corresponds to the point N on the curve SAO, 
 the distance QR being 13 per cent of QS. 
 
 In the same manner the curves SCG, SDH, and SEK are drawn 
 showing the conditions when the station P carries 40 per cent, 60 
 per cent, and 80 per cent, respectively, of the total load. The 
 summit of the curve SMD, in which the station P carries 60 per 
 cent of the load, is located so that PL equals 60 per cent minus 
 33 per cent, or 27 per cent of the total length SQ to the left of P. 
 The distance QL is, therefore, 60 per cent of the total length QS. 
 
 In general, the conditions are more complicated than those 
 here assumed, and will ordinarily prevent an accurate determina- 
 tion of the relative potentials of the negative buses of the two 
 stations. 
 
 (d) Economic Considerations Invoked in Additional Supply 
 Stations. The practical limit of feeding distances is one that 
 cannot be determined by any general formula designed to fit all 
 conditions. The economic aspects of the problem are far more 
 complex than they appear at first glance and the proper solution 
 involves a careful study of local conditions. However, an increase 
 in the number of power supply stations may be said generally to 
 reduce stray currents to a marked degree and with the advent of 
 automatic control for railway substations the increase in the 
 number of feeding points economically obtainable by this means 
 should result in greatly improved electrolysis conditions. 
 
 The number of substations for a given set of conditions may 
 often be materially increased by some additional capital expendi- 
 
DESIGN, CONSTRUCTION, OPERATION, ETC. 
 
 43 
 
 ture, but with no increase in annual charges. Also, the original 
 equipment may be distributed to additional stations with little 
 or no capital expenditure, due to saving of feeder copper, and 
 with no increase in annual charges. 
 
 Number of Substations 
 
 Relation of Number of 5ubsfa4ions -fo Annual 
 Cnaraes -for Interurban Line 
 
 Fig. 7. 
 
 The curves in Fig. 7 show the results of calculations on a typical 
 interurban railway system. They are based on the data con- 
 tained in the paper by H. F. Parshall presented to the (British) 
 
44 DESIGN, CONSTRUCTION, OPERATION, ETC. 
 
 Institute of Civil Engineers, Volume 199; and on present day 
 prices of copper and electrical machinery and labor. 
 
 Ordinarily in laying out the number of substations for a given 
 electric railway system, the minimum number consistent with 
 economy will be the number selected, such as represented by the 
 curve for manual operation at A. With the growth of traffic 
 the number of stations in operation becomes increasingly inade- 
 quate until a condition is reached represented by the point B on 
 the curve, when additional substations are again added. In 
 other words it is customary to operate along the curve from A to 
 B with an insufficient number of substations. It appears, how- 
 ever, that by operating between C and A on the curve instead of 
 between A to B an increase of about 40 per cent in the number of 
 substations can be made without effect on the total annual charges. 
 
 It has been shown on page 40 of this report that when the 
 overall voltage is divided by 4 the amount of stray current will 
 be about one-sixth for the particular conditions discussed. An 
 increase of 40 per cent in the number of substations will decrease 
 the overall voltage to about one-half of the former value and there- 
 fore reduce the stray current to about one-third. It appears, 
 therefore, that by selecting the maximum number of substations 
 consistent with economy instead of the minimum number, the 
 railway companies could reduce to a large extent the stray currents 
 without appreciably affecting their total annual charges and this 
 method should be considered as one of the best possible solutions 
 of the electrolysis problem. The curve for automatic substations 
 is even flatter than that for manually operated stations, indicating 
 that a very large increase in the number of automatic stations 
 beyond the point of maximum economy may be employed without 
 materially increasing the annual charge. 
 
 It appears from these curves that if, while the electric railway 
 companies are increasing their power supply, they will at the same 
 time increase the number of power supply stations to the maximum 
 economical number, then they can without any increase in the 
 total annual charges eliminate the greater portion of the stray 
 currents which cause electrolysis. 
 
 In many situations the combination of railway substations with 
 light and power substations may offer additional opportunities 
 for economically providing points of supply without additional 
 expense for buildings and attendance. 
 
 (e) Automatic Substations. During recent years considerable 
 progress has been made in the development of automatic, semi- 
 
DESIGN, CONSTRUCTION, OPERATION, ETC, 45 
 
 automatic, and remote control substations for electric railway 
 service. 
 
 Automatic stations were first used on interurban lines having 
 infrequent service and the installation usually consisted of a 300 
 or 500 kw. machine. When a car or train of cars approaches one 
 of these interurban substations the voltage of the trolley falls 
 and when it has reached a certain point the substation auto- 
 matically starts up and carries the load while the train is in its 
 vicinity. As the car recedes from the substation the demand for 
 current decreases and when the load has reached a predetermined 
 minimum the substation shuts down. 
 
 This type of substation with small converters has been success- 
 fully introduced in some cities, the most notable installation being 
 that at Des Moines, Iowa, where six substations were distributed 
 throughout the city to replace one centrally located power supply 
 station. 
 
 The characteristics of large city loads are different from those 
 on interurban lines. The movement of a single car produces but 
 slight fall in the trolley potential and the starting and stopping 
 of the substation is governed by the demand for power during the 
 morning and evening rush hours. A few substations with large 
 converters have been provided for such city service and are now 
 in experimental operation. Remote control substations are also 
 being developed for city service where they are required to operate 
 continuously throughout the load period of the day or during the 
 morning and evening peaks. 
 
 Semi-automatic equipment, consisting of re-closing circuit 
 breakers, time switches, and protective devices have been installed 
 in a number of railway substations at a very much smaller cost 
 than would be required for full automatic operation. The circuit 
 breakers in the positive feeders automatically re-close after a 
 definite time interval provided the short circuit or overload has 
 been removed. The synchronous converter has to be started by 
 hand and may be shut down either by a time switch or by hand. 
 Otherwise it operates in a manner similar to those provided with 
 full automatic control. 
 
 The first cost of automatic substations is often justified by the 
 saving in operating labor an_d feeder losses and the recovery of 
 existing feeding copper. Minor savings arise from the elimination 
 of light load losses and the station heating. A further benefit also 
 to be derived from their general use is better voltage conditions 
 and therefore faster car schedules. 
 
46 DESIGN, CONSTRUCTION, OPERATION, ETC. 
 
 The total amount of substation equipment now operated auto- 
 matically is in excess of 50,000 kw., and much of the equipment 
 being installed is intended for automatic operation or remote 
 control. The increased savings attending this development will 
 undoubtedly increase the number of substations which can 
 economically be installed on both interurban and city systems, 
 and if full advantage is taken of these economics, the feeding 
 distances will be reduced to such an extent as to greatly reduce 
 stray currents generally. 
 
 ( f ) Location of Supply Stations. As pipes and other under- 
 ground structures become increasingly positive to the earth as 
 they approach street railway supply stations or the low potential 
 points on the track system, it is obvious that if stations were 
 located away from pipe networks trouble from electrolysis would 
 seldom occur. As a rule other considerations will determine 
 the location of supply stations in cities. However, on interurban 
 lines the protection of piping systems in small towns against 
 electrolytic corrosion often presents a grave problem because of 
 the long feeding distances and the difficulty of employing the 
 measures of mitigation ordinarily used in city systems. Under 
 such conditions the location of the supply station at a distance 
 from the city and away from the underground structures may be 
 the most satisfactory way of insuring their protection. This is 
 particularly true of automatic substations which require no 
 regular attendants. 
 
 The character of the earth in the vicinity of supply stations 
 naturally has an important effect on the magnitude of stray 
 currents. It is, therefore, desirable to avoid connecting negative 
 feeders to tracks in unusually wet locations. 
 
 (g) Alternating Current Systems. When the first alternating 
 current railways were proposed, the question of possible electrolytic 
 effects received special investigation. Considerable work was 
 done upon a laboratory scale, in which it was established that 
 alternating currents could produce corrosion on electrodes of the 
 metals commonly used underground, such as lead and iron, but 
 that the effects were very much less in magnitude than those 
 produced by equivalent direct currents, usually less than one per 
 cent and in most cases negligible. See Fig. 16. 
 
 The objections to the substitution of alternating current for 
 direct current in the case of systems already installed in large 
 cities are so well known and so serious that the question needs no 
 discussion. 
 
DESIGN, CONSTRUCTION, OPERATION, ETC. 47 
 
 5. Interconnection of Tracks. 
 
 Electrical interconnection between parallel tracks in close 
 proximity, or of tracks, one of which passes over the other, be- 
 longing to the same or different railway systems is usually a 
 necessity in order to prevent wide fluctuations of voltage between 
 the tracks. Such interconnections tend to equalize the potentials 
 of the tracks so connected and thus tend to prevent the flow of 
 current from the track of high potential through earth and inter- 
 vening metallic subsurface structures to the track of low potential. 
 In general such interconnections also afford a saving in track losses. 
 
 Whether parallel tracks should be connected naturally depends 
 upon the distance between tracks, location of supply stations, 
 leakage characteristics of the roadbeds and other local con- 
 siderations. 
 
 Interconnection generally reduces the track voltage drop by 
 providing more metallic paths for the current. It has also the 
 same general effect as cross-bonding between rails of the same 
 tracks, in that if one track circuit should be accidentally opened 
 the current would be shunted around through the interconnection 
 to the other track. As a rule interconnection of tracks will 
 improve electrolysis conditions but may be detrimental to one 
 locality while improving conditions in another. A failure of one 
 of the companies to maintain its bonding would naturally tend to 
 increase the current on the better bonded track. 
 
 Interconnection of tracks has been found to be particularly 
 advantageous where two or more lines of electric railways operating 
 in one locality and belonging to the same or to different systems 
 are supplied from two or more power stations located in different 
 parts of the city. By interconnecting the tracks of such lines in 
 the neighborhood of the power stations and also at several inter- 
 mediate points a reduction in the resistance of the return circuit 
 can be brought about whereby the drop formerly existing in one 
 track can be balanced by the drop in the opposite direction in the 
 other track. The rail drop in each track is greatly reduced and 
 all high potential gradients between tracks eliminated. 
 
 Where the tracks of the two independent railway systems are 
 parallel and a short distance apart, and fed by power supply 
 stations in opposite directions the potential profiles of the rails 
 will be as shown in Fig. 8 in which, for simplicity, the negative 
 buses at the two stations have been assumed to be at the same 
 potential. In the figure are also indicated the potential profiles 
 of the pipes adjacent and parallel to the two sets of tracks. 
 
48 
 
 DESIGN, CONSTRUCTION, OPERATION, ETC. 
 
 If then gas or water pipes extending from the parallel mains 
 cross under two sets of tracks at different locations where the 
 tracks are at a considerable difference of potential, as at RB, Fig. 
 8, then the pipes may be negative to one track and positive to the 
 
 Station A 
 
 Station B 
 
 Potential Profile 
 
 oftwo Independent Railway Systems 
 Sho wincr Effect of Interconnection 
 
 Fig. 8. 
 
 other. At the crossings where the pipes are positive to the tracks 
 electrolysis will be liable to occur. 
 
 If now the rails of the two systems are interconnected at points 
 near the two stations and also at intermediate points the potential 
 profile along the rails after such interconnection will be as shown 
 by the curve OYP. It will be noted that this interconnection 
 
DESIGN, CONSTRUCTION, OPERATION, ETC. 49 
 
 results in a very considerable reduction of the potential drop in 
 the return circuit, and the resulting reduction in the losses will 
 in many cases be alone sufficient to warrant the cost of the inter- 
 connections. 
 
 Railway systems employing track circuit signals must insulate 
 their rails used for signal circuits from other systems in order that 
 other currents may not be introduced in the signal circuits and 
 for this reason cannot avail themselves of the advantages of inter- 
 connection. This applies only to rails used for signal circuits. 
 
 B. FEATURES OF RAILWAY CONSTRUCTION AND 
 
 OPERATION EMPLOYED FOR ELECTROLYSIS 
 
 MITIGATION 
 
 1. Insulated Negative Feeder System. 
 
 Of the various methods of railway construction and operation 
 employed to improve electrolysis conditions, the insulated nega- 
 tive feeder system has been most widely used. While it has been 
 generally thought that such a system is necessary in connection 
 with a large supply station if underground structures are to re- 
 ceive adequate protection, the present tendency to greatly increase 
 the number of railway supply stations, and particularly the 
 development of the automatic substation makes the extensive 
 use of insulated negative feeders less important. An increase in 
 the number of track drainage points is often more economically 
 attained by the use of more substations than by the use of insulated 
 negative feeders. The tendency is now in the direction of a 
 relatively few short insulated negative feeders and a large num- 
 ber of substations, rather than an extensive use of insulated feeders 
 from a few large supply stations. 
 
 (a) Description. In the insulated negative feeder system, 
 instead of tying the tracks directly to the negative bus and de- 
 pending on the tracks and such copper conductors as may be in 
 parallel with them to return the current to the supply station, the 
 connection at the station is either removed or a suitable resistance 
 is inserted and insulated feeders are run from the bus to various 
 points on the track. By thus taking the current from the rails 
 at numerous points, high current densities, and consequently 
 high gradients and overall voltages, can be avoided to any desired 
 degree. As the feeders are entirely insulated from the earth 
 except at points of connection to the tracks, the actual drop in 
 potential in the different feeders is of no importance so far as 
 electrolysis is concerned, so long as the drop is approximately 
 
50 
 
 DESIGN, CONSTRUCTION, OPERATION, HTC. 
 
DESIGN, CONSTRUCTION, OPERATION, ETC. 51 
 
 the same in all feeders. It is possible, therefore, to impose any 
 limiting value of overall-track drops and track potential gradients 
 on the track and still be free to design the feeders to give maximum 
 economy which is not possible when the feeders are connected in 
 parallel with the track. 
 
 Insulated feeders are sometimes designed for equal potential 
 drops, in which case the several points of connection to the tracks 
 are at the same potential and the system is called an equi-potential 
 or balanced system. When the shorter feeders are designed for a 
 lower drop than the longer feeders, the system is called a graded 
 potential system. 
 
 Fig. 9 shows the overall voltage curves representing conditions 
 on a track which is connected directly to the negative bus and 
 with which no additional feeders are employed. The curves are 
 parabolas with the same constants as those in Figs. 2 and 5. Fig. 
 10 illustrates the same system with insulated negative feeders 
 extended to four points on the track, two in each direction, with 
 a resistor connected to the nearest point on the track. The 
 feeders and resistance are so proportioned that the drop on all is 
 the same under average load conditions and they, therefore, form 
 an equi-potential system. The curved lines represent the poten- 
 tial of the track from point to point, and, as in Fig. 9, the curves 
 are arcs of parabolas. 
 
 An equi-potential system of this kind, while it reduces potential 
 differences on the tracks to a minimum and therefore affords the 
 maximum reduction of stray current, usually involves increased 
 energy losses in the return circuit as the rails are merely used 
 as distributing mains for the feeders and are not taken advantage 
 of to return current to the supply station. The equi-potential 
 principle is better adapted to a city network than to a single line, 
 as feeders can be extended to several points on the network at 
 approximately the same distance from the station, and these 
 points can thus be maintained at the same potential. As a rule, 
 however, a gradient is permitted between the points so selected 
 and the track at its nearest approach to the supply station. An 
 arrangement approaching an equi-potential system is shown in 
 Fig. 1 1 , where four feeders are connected to the track at important 
 intersections and connection made to the track near the station 
 through a resistance. One of the feeders is shown connected to^ 
 the track at two points, a resistance being inserted at the point 
 nearest the station. 
 
 This system and also the one illustrated in Fig. 10 are practically 
 
52 
 
 DESIGN, CONSTRUCTION, OPERATION, ETC. 
 
DESIGN, CONSTRUCTION, OPERATION, ETC. 53 
 
 equivalent, in the reduction of stray currents, to independent 
 substations at the several points where the current is removed 
 from the track; that is, the results, so far as voltage drop on the 
 tracks is concerned, is the same whether a number of stations or 
 an equal number of insulated negative feeders be employed, but 
 the energy losses in both the positive and negative conductors are 
 very much greater with the negative feeder system than with the 
 same number of substations. 
 
 Fig. 12 illustrates an insulated negative feeder system so de- 
 signed that the direction of the current in the rails is not reversed 
 as in the equi-potential system. This graded potential system 
 results in a slightly higher potential at the terminal of each suc- 
 ceeding feeder, starting from the station, and these higher poten- 
 tials on the longer feeders result in higher overall track potentials 
 than with the equi-potential system, but allow a material saving 
 in copper in the negative conductors. 
 
 In designing graded potential feeder systems, it is customary to 
 limit the gradients on the tracks to some definite amount, such, 
 for example, as an average value of 0.5 volt per 1000 feet and to 
 remove all of the current from the track over an insulated feeder 
 wherever this limiting gradient is reached. By removing no more 
 current at any point than has accumulated up to that point, the 
 current in the track is nowhere reversed and a continuous gradient 
 toward the station is maintained as illustrated in Fig. 12. 
 
 (b) Application of Insulated Negative Feeders. No definite 
 rules can be laid down regarding when and to what extent insu- 
 lated negative feeders should be used. In city networks the 
 negative bus should generally be connected to the track at more 
 than one point, that is, negative feeders should be extended along 
 the tracks to nearby intersections. Small stations of 300 to 500 
 k.w. capacity in city networks may usually be connected directly 
 to the track at one point only and preferably to the nearest track 
 intersection. 
 
 Insulated negative feeders should be run from the negative bus 
 to the rails in such a manner as to insulate them thoroughly from 
 the earth and from each other. The tying together of any of these 
 feeders should be avoided. In some cases, however, it may be 
 allowable to tie a single feeder to the rail at two or more points 
 through resistances to adjust the currents drawn from the tracks 
 at the various points of connection. 
 
 Connections to tracks in wet locations make possible excessive 
 
54 
 
 DESIGN, CONSTRUCTION, OPERATION, ETC. 
 
 
 I 
 
 Q> 
 
 "0 
 
 
 o 
 
 I 
 
DESIGN, CONSTRUCTION, OPERATION, ETC. 55 
 
 current^discharge from adjacent underground structures and 
 should therefore be avoided where possible. 
 
 Means should be provided on all negative feeders and feeder 
 taps for conveniently measuring the current flow thereon, and 
 where practicable these means should be installed within the 
 railway power station. 
 
 Application to Interurban Lines. In the case of a single line, 
 little is to be gained by the use of insulated negative feeders unless 
 they are run considerable distances from the power supply station. 
 For this reason they are not as well adapted to reducing stray 
 currents from interurban lines as from city networks as the follow- 
 ing explanation will show. 
 
 It has been shown in the section on Power Supply that stray 
 current results from the action of large overall voltages rather 
 than from high potential gradients. Large overall voltages may 
 be produced either by concentrated city loads over relatively 
 short feeding distances or by comparatively light loads on long 
 lines. The former condition can often be effectively dealt with 
 by the use of insulated feeders because of the short distances in- 
 volved and a traffic of sufficient density to justify such an ex- 
 penditure. A very different condition exists on interurban lines 
 where a corresponding reduction in overall voltages would require 
 very long insulated feeders entailing large expenditures for copper 
 and large power losses. 
 
 The effect of installing insulated negative feeders within the 
 limits of a small town through which an interurban lines passes 
 is illustrated in Fig. 13. Without the use of negative feeders, that 
 part of the piping system within the city limits is shown to be 
 positive to the tracks, a condition which is often found in practice, 
 although not a reliable criterion as to the degree of hazard to 
 underground structures as pipes are sometimes positive to the 
 rails and negative to the adjacent earth. If the potential gradients 
 on the tracks within the city are reduced or eliminated by the use 
 of insulated feeders, the overall voltages are only slightly affected 
 and the potential difference between the pipes and tracks not 
 greatly reduced. In some instances where insulated feeders have 
 been applied on interurban lines, the positive area has actually 
 been extended and no material improvement in the general 
 condition effected. 
 
 It is not the intention here to condemn entirely the use of insu- 
 lated^negative feeders for interurban electric lines, because in 
 some cases they have been successfully used. Local conditions 
 
56 
 
 DESIGN, CONSTRUCTION, OPERATION, ETC. 
 
DESIGN, CONSTRUCTION, OPERATION, ETC. 57 
 
 vary widely and each problem should, therefore, be worked out on 
 its own merits. However, it can safely be said that this method 
 of electrolysis mitigation is not so well adapted to interurban 
 lines as to city systems. 
 
 (c) Negative Boosters. Negative boosters are sometimes used 
 in connection with the insulated negative feeder system abroad, 
 but not in this country, so far as known. Unusually long feeders 
 which would have to be very heavy in order to keep the voltage 
 drop comparable with that on the other feeders can be reduced to 
 the minimum size that will carry the current if provided with a 
 booster. When so used, the booster permits a saving in copper 
 but involves an additional energy loss on the conductor. Boosters 
 can also be used to equalize the voltage drops on feeders of differ- 
 ent lengths. They have proved economical under certain condi- 
 tions and uneconomical under others. In general it is simply a 
 question of the fixed charges on copper as against the fixed charges 
 and operating cost of machines. 
 
 2. Three-Wire System. 
 
 (a) Description. This method of power distribution is similar 
 to that commonly used for city light and power, and known as the 
 Edison three- wire system. It may take two different forms which 
 are the same in principle, but which differ radically in the arrange- 
 ment of the feeder system. One of these, known as the parallel 
 three- wire system, is directly analogous to the ordinary three-wire 
 power and lighting system. The typical arrangement for the case 
 of a double-track line using this system is shown in Fig. 14. Here 
 one trolley is negative and the other positive, the tracks being 
 the neutral conductor. This results in a potential difference be- 
 tween trolley wires equal to twice the operating voltage at points 
 of connection between the trolley sections. It is evident that 
 only the difference in the load on the two sides of the line returns 
 to the powerhouse on the track, although there may at times be 
 heavy circulating currents flowing between cars in short sections 
 of track. If the cars run at frequent intervals, however, such cir- 
 culating currents will not have to flow over sufficiently great dis- 
 tances in the tracks to cause nearly as large track drops as would 
 occur with the same loads under two-wire operation. The result 
 would be that where load conditions are reasonably favorable for 
 the three- wire system, large reductions in potential drops in the 
 negative return could be secured. 
 
 While almost perfect electrolysis conditions could be obtained 
 
58 
 
 DESIGN, CONSTRUCTION, OPERATION, ETC. 
 
 o 
 
 $ 
 
 D 
 
 
 . 
 
 Neu-traK ] 
 
 s~* 
 
 <-, 
 
 > 
 
 i 
 
 y 
 
 1 
 
 Positive Feeder^ 
 
 jystem 
 ^ Positive Feeder ^_ 
 
 -4 
 
 > 
 
 rOi 
 
 
 | 
 
 Negative Feeder/ 
 Sectionali-Ered Three Wire System 
 
 Fig. 15. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 Parallel Three Wire S 
 
 Fig. 14 
 
 
 
 
 r- 
 
 f 
 I 
 
 
 
 
 
 Trolley Wire^ | ] 
 
 
 
 
 
 
 
 ? j 
 
 
 
 
 
 
 
 
 j 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 2 
 
 
 
 K ? 
 
 * 
 
 
 
 Tracks 
 
 
DESIGN, CONSTRUCTION, OPERATION, ETC. 59 
 
 with the parallel three-wire system, the difficulty of properly in- 
 sulating the two trolley wires from each other, especially at cross- 
 ings and switches, has been considered so great that the sectional- 
 ized three-wire system is considered the more practicable and has 
 therefore been employed in all installations which have come to 
 our attention. It is shown diagrammatically in Fig. 15. 
 
 In this form the feeding district is divided into sections, and 
 alternate sections are supplied by feeders running from the positive 
 bus, while the remaining sections are supplied by feeders from the 
 negative bus, the difference of potential between the two buses 
 being approximately 1,200 volts. In this way, the existence on the 
 same portion of the street of two trolleys having a high difference 
 of potential between them is avoided. The tracks, as before, 
 serve as the neutral conductor and convey the current from the 
 cars in one section to those in the adjoining section and return the 
 unbalanced current to the powerhouse. 
 
 (b) Insulation of Trolley Sections. The problem of insulating 
 the positive and negative trolley sections from each other is one 
 that will require considerable care. At points of simple junc- 
 ture this has been accomplished in some cities by the use of 
 two standard 600-volt trolley section insulators in series, with 
 a dead section of trolley wire from 4 to 6 feet in length between 
 them. In other cities the two section insulators are brought to- 
 gether, thereby simplifying the overhead construction. It is also 
 possible to use a single 1,200- volt section insulator 18 to 24 inches 
 long. Where trolley wires of opposite polarity cross, it will 
 probably be found better to make the entire intersection of one 
 polarity rather than try to insulate the crossings. At the inter- 
 section of two double-track lines this will mean the installation 
 of four double section insulators as just described. Where such 
 changes are made, the more important of the two lines should be 
 made the continuous one to avoid interruption of service due to 
 failure of power on the other line. Warning signs should be hung 
 on the span wire at all section insulators and motormen should be 
 instructed to coast across these points. 
 
 (c) Costs. The principal economy resulting from the installa- 
 tion of the three-wire system, is the saving in track losses, which 
 are greatly reduced, although not entirely eliminated, while there 
 usually will be increased station losses due to the necessity of 
 always operating two sets of generators or converters. 
 
 In systems having a relatively small number of multiple unit, 
 power supply stations, the cost of converting a system for three- 
 
60 DESIGN, CONSTRUCTION, OPERATION, ETC. 
 
 wire operation is usually, but not always, smaller than the first 
 cost of insulated negative feeders, or any other measure that will 
 give the same degree of protection from electrolysis. The avail- 
 able data on three-wire systems, both as to costs and effects of 
 electrolysis conditions are not sufficient to warrant the laying 
 down of general rules as to the extent of its application. The 
 local factors involved in each case are often peculiar and require 
 special consideration. 
 
 In cities where uninsulated negative copper has been installed, 
 it may be reclaimed after conversion to three- wire operation, 
 unless it has been installed under pavement or embedded in con- 
 crete, and the salvaged copper may largely, if not entirely, cover 
 the cost of conversion. 
 
 It is good practice to provide an additional bus in the supply 
 station for the generators and feeders operated with reverse 
 polarity. Double throw switches are also installed for these 
 feeders and generators. 
 
 (d) Difficulties and Limitations. One difficulty which some- 
 times will be encountered in three-wire operation is that of re- 
 duced station capacity, as two or more machines operating in 
 parallel will have a much greater capacity at times of excessive 
 demand than when divided on two independent circuits. Heavy 
 interurban trains, particularly when starting, often demand the 
 full capacity of a supply station and the same condition exists at 
 times of unusual loads, such as occur after a tie-up or following a 
 ball game or circus. Where the generating capacity of both the 
 positive and negative sides of the system is large in comparison to 
 the maximum demand of any trolley section, this objection does 
 does not exist, but where only a single small machine is available 
 for one side of the load, considerable difficulty may be encountered 
 in taking care of the peak demands under extreme conditions. 
 Where necessary these extreme peak demands can be taken care 
 of by operating all of the machines on one polarity during this 
 period. Double throw switches, by which this can quickly and 
 conveniently be accomplished, are usually provided with three- 
 wire operation. 
 
 One instance of an overload with three-wire operation resulted 
 in the too frequent blowing of the circuit breaker on the negative 
 generator. This was eventually overcome by installing a series 
 resistance which is automatically cut into the circuit when the 
 current reaches a predetermined maximum value, thereby limiting 
 the current to a fixed amount. The equipment used for this pur- 
 
DESIGN, CONSTRUCTION, OPERATION, ETC. 61 
 
 pose is identical with that employed for. automatic railway sub- 
 station control. 
 
 Not only are unusual loads of short duration difficult to take 
 care of with three- wire operation, but where the entire capacity of 
 a station with all machines in parallel is required to carry the 
 normal peak-load, it may be impractical to convert for three- 
 wire operation. In general, it will, of course, be difficult to 
 divide the positive and negative loads in the same ratio as the 
 capacities of the two groups of generators assigned to them. 
 Moreover, the load factor of the whole system is always greater 
 than that of any part, and the generators when divided into 
 groups will therefore be operating at poorer load factors and con- 
 sequently at lower efficiencies than. when in parallel. Therefore, 
 where no excess generator capacity exists, it may sometimes be 
 necessary to install an additional unit in converting a system for 
 three- wire operation. 
 
 Owing to the continual movement of cars from one trolley 
 section to another of opposite polarity, there is a considerable 
 variation in the track potential at any point. This is particularly 
 true on lightly loaded lines and results in wide fluctuations, and 
 even reversals, between the tracks and adjacent underground 
 structures. While the algebraic average values of such potential 
 differences may be greatly reduced by the adoption of a three-wire 
 system, a continuously negative condition of underground struc- 
 tures cannot ordinarily be expected. 
 
 Other difficulties of less importance have been suggested: (1) 
 Some equipment, such for example as arc-headlights, ampere- 
 hour-meters and auxiliary battery control, requires a single 
 polarity for its successful operation. Where such equipment is 
 used it will be necessary to provide reversing switches. (2) Two 
 trolley poles in parallel cannot be employed on a single car or on 
 trains as they would bridge trolley sections of opposite polarity 
 when moving across section breakers. (3) A negative trolley 
 would change the character of the electric arc used on tracks for 
 arc- welding and building up joints and in some operations might 
 be objectionable. (4) Commercial customers receiving power 
 from trolley feeders may, in some cases, be inconvenienced by a 
 change of polarity. 
 
 (e) Practicability. None of the difficulties here cited can be 
 considered of insurmountable character, and like many other 
 things, the system can be made to work satisfactorily if the neces- 
 sary attention is given to it. Experience has fully demonstrated 
 
62 DESIGN, CONSTRUCTION, OPERATION, ETC. 
 
 that it will greatly improve electrolysis conditions when properly 
 applied and also give better operating voltage at the cars. How- 
 ever, to secure the best possible results with this system, it will 
 often be necessary to change feeder copper and shift section in- 
 sulators to obtain the desired sectionalization 
 
 . (f) Extent oj Adoption, Until recent years the three-wire 
 system has not been employed for street railway work in this 
 country, although it has been in use in Brisbane, Australia, and 
 Nuremberg, Germany, for a number of years. In the last few 
 years it has received some attention in America and is now in 
 operation in Omaha, Wilmington, Winnipeg, Canada, and in some 
 portions of Los Angeles and Milwaukee. 
 
 The Los Angeles installation has been in operation since 1915 
 and more recently has been extended to include several additional 
 station districts. In Omaha a trial installation in one station 
 district was made early in 1917. After several months' trial with 
 the experimental installation, the main station district was con- 
 verted for three-wire operation and has since been so operated. 
 
 Three-wire operation was adopted in Winnipeg as a means of 
 meeting the requirements of a law passed by the Manitoba Legis- 
 lature, prescribing certain limitations in track voltage drops. 
 Two substation districts were changed over in 1919, and since 
 that time practically the entire system has been converted to 
 three-wire operation. 
 
 In 1920, after considerable experimenting, a three-wire system 
 was substantially completed in Wilmington, Delaware, and a 
 complete electrolysis survey made under both two-wire and three- 
 wire operation. With the latter, a considerable improvement in 
 car operation due to higher average voltage was reported, and 
 also better electrolysis conditions on water and gas pipes. Stray 
 currents and overall potentials were reduced to about one-half 
 their values with two- wire operation. Reversing potentials were 
 found on the telephone cables in some areas and some adjustment 
 of the drainage of this system will be necessary before it can be 
 said to be entirely satisfactory. 
 
 3. Reversed Polarity Trolley System. 
 
 This method of railway operation involves using the running 
 tracks as the positive conductor instead of the trolley wire. 
 It has at various times been suggested as a means of electrolysis 
 mitigation, and in at least one case it has received an extended 
 trial.. Fundamentally, however, it is not a mitigation method, 
 
DESIGN, CONSTRUCTION, OPERATION, HTC. 63 
 
 because it merely reverses the direction of the stray current and in 
 no way affects the magnitude thereof. With reversed polarity the 
 same amount of corrosion will result as with normal operation and 
 the only difference will be the localities in which the damage will 
 occur. Under normal operation using the running tracks as the 
 negative conductor, the electrolytic damage will generally be con- 
 fined to the area immediately surrounding the direct current power 
 station or the track feeder connection points. With reversed po- 
 larity, the electrolytic corrosion will be scattered over the out- 
 lying districts which with normal polarity would constitute a 
 negative area. If the trolley system is operated with reversed 
 polarity, it is extremely difficult to effectively drain the lead 
 sheaths of underground cable systems, because there is no definite 
 point of low potential to which to drain. 
 
 In 1912 the polarity of the electric street railway system in 
 New Haven, Connecticut, was reversed making the running tracks 
 the positive conductor. This method of operation was adopted 
 by the railway company in order to afford immediate relief to the 
 gas works, and to the water and gas piping systems in the central 
 part of New Haven, where very serious damage was occurring. 
 It was then thought that in the outlying sections the damage would 
 be less concentrated, and also failures would be less serious and 
 more easily repaired, than in the central business district. It soon 
 became evident that it was practically impossible to adequately 
 drain the underground telephone cable system, and that even with 
 reversed polarity the general electrolysis conditions of the water 
 and gas piping systems were still far from satisfactory, and after a 
 trial of eight years, this method of operation was abandoned. 
 
 The New Haven experiment therefore, indicates that the 
 reversal of railway polarity to rails positive is merely a means of 
 relieving dangerous electrolysis conditions in the vicinity of the 
 power station, at the expense of the cable and piping systems at 
 some distance from the station. When no underground cable 
 systotns are involved, reversed polarity is useful as a temporary 
 means of immediate relief to an endangered piping system in 
 the interval immediately preceding the installation of effective 
 electrolysis mitigation. 
 
 4. Periodic Reversal of Trolley Polarity. 
 
 If the polarity of the trolley is reversed daily, at a time when 
 the load on the system is a minimum, few operating difficulties 
 will be encountered and some improvements in electrolysis condi- 
 
64 
 
 DESIGN, CONSTRUCTION, OPERATION, ETC. 
 
 tions will result. It is obvious that pipes in any locality will be in 
 a positive condition only half as long as with normal operation, 
 and there may also be a further reduction of electrolysis due to 
 redeposition of the corroded metal during the period when the 
 
 
 
 
 
 
 
 
 
 
 
 
 t" 
 
 
 
 V /n 
 
 
 Co efficient of Corrosion 
 at 
 Different Frequencies 
 of 
 Iron Electrodes in Soil. 
 
 
 ^- 
 
 
 
 s 
 
 s 
 
 
 
 / 
 
 a eo 
 
 *so 
 
 
 
 
 
 
 
 
 
 / 
 
 
 40 
 
 
 
 
 
 
 
 
 
 7 
 
 
 U 30 
 
 
 
 
 
 
 
 
 y 
 
 / 
 
 
 * 
 
 
 
 
 
 
 
 
 / 
 
 
 
 "t 20 
 
 
 
 
 
 
 ^ 
 
 x^ 
 
 ^ 
 
 
 
 !o 
 
 
 . -* 
 
 . 
 
 * 
 
 ^^ 
 
 
 
 
 
 
 <s 
 
 
 
 
 
 
 
 
 
 
 
 o -fa 15 55 I 5-IO 6O 2. 14- Direct 
 
 Sec. Sec. Min. Days Current 
 
 Logarithm of Length of Time of One Cycle. 
 
 Variation of Coefficient of Corrosion 
 of Iron with Frequency 
 
 Fig. 16. 
 
 pipes are negative. Laboratory experiments made by the Bureau 
 of Standards, the results of which are shown in Fig. 16, indicate 
 that with a daily reversal of polarity, the corrosion of iron pipes 
 at any point will be about twenty-five per cent as great as will 
 result without such reversals. A similar relation, though not 
 
DESIGN, CONSTRUCTION, OPERATION, ETC. 65 
 
 precisely the same as that shown in Fig. 16 exists with respect to 
 lead when subjected to periodically reversed currents. 
 
 This method of operation has been employed by the Pacific 
 Electric Railroad Company of Los Angeles, since 1918 in Pomona, 
 Redlands, San Bernardino, Riverside, and Corona. In general it 
 is not applicable to cities where lead cable systems are installed 
 underground, as it would greatly complicate and sometimes 
 render impracticable the drainage of such systems. However, 
 where the cable system is small and confined to the vicinity of the 
 power supply station it may be drained satisfactorily through an 
 automatic switch which permits current to flow from the cables, 
 but automatically prevents the reversal of such flow. 
 
 Some of the operating difficulties discussed in connection with 
 three-wire systems will be encountered with this system. The 
 operating difficulties attending a more frequent reversal of the 
 trolley potential would be considerably greater, and no attempt 
 so far has been made to do this. 
 
 5. Double Contact Conductor Systems. 
 
 The double overhead trolley system of electric traction as at 
 present used in Cincinnati, and the corresponding underground 
 conduit systems as used in Washington and in parts of New York 
 City, if properly maintained, eliminate the danger of electrolysis. 
 This system has in past years, been strongly urged by some pipe 
 owning companies and engineers who believed it to be the only 
 method by which complete immunity from electrolysis could be 
 obtained. It is now generally recognized, however, that a sub- 
 stantial degree of protection can be obtained by less expensive 
 and objectionable methods and the demand for the double contact 
 conductor system is, therefore, not being pressed at the present 
 time. The chief objections to its use are the cost of installation 
 and the increased operating difficulties which it involves, as well 
 as an unsightly appearance of the streets in the case of the double 
 overhead trolley. The double contact underground system, as 
 used in New York and Washington, not only removes the source 
 of stray current, but requires no overhead wiring or poles and in 
 rare cases may be justified or required for that reason alone. 
 Merely as a means of electrolysis mitigation, the increased cost 
 of the double contact conductor system does not appear to be 
 justified. 
 
66 DESIGN, CONSTRUCTION, OPERATION, ETC. 
 
 II. UNDERGROUND STRUCTURES SUBJECT TO 
 INJURY BY STRAY CURRENTS 
 
 A. LOCATION WITH RESPECT TO TRACKS 
 
 In general, the problem of protection from stray currents has 
 to do with conditions under which the affected structures and the 
 tracks are already in place, that is, where their respective locations 
 are fixed. In the great majority of instances, therefore, a dis- 
 cussion of the most favorable relative location of underground 
 structures and rails can have but little more than an academic 
 interest. However, in laying new underground structures or 
 replacing old ones, it is in the interest of safety to locate them at 
 as great a distance from the rails as possible. Usually condi- 
 tions other than electrolysis determine the location of mains, 
 but where it is possible to locate mains on both sides of a street 
 having car tracks, such construction prevents the crossing of 
 service pipes under tracks and is in the interest of good electrolysis 
 conditions. Where mains or services must cross under tracks 
 there is a considerable advantage in having them as deep . as 
 possible, but a depth of more than 4 or 5 feet is ordinarily not 
 justified. 
 
 B. CABLE SYSTEMS 
 
 1. Avoidance of Accidental Contacts with Other Structures. 
 
 From an electrolysis standpoint, it is usually necessary to treat 
 lead sheath cables as distinct from other underground structures 
 due to the fact that lead is appreciably more susceptible to corro- 
 sion from stray current than iron, and also because different 
 measures are usually applied to the protection of lead sheath 
 cables than to other underground metallic structures. One am- 
 pere flowing steadily for a year will carry into solution about 20 
 pounds of iron or about 74 pounds of lead. This high electro- 
 chemical equivalent of lead and the thin walls ordinarily used for 
 cable sheaths require that unusual care be exercised in their 
 protection. 
 
 In the Bell Telephone System precautions are taken to avoid 
 contact between its lead sheathed cables and other underground 
 structures, such as foreign cables, rails, steel bridges, gas or water 
 piping system and the metallic structure of steel-frame buildings. 
 Where it is necessary that cables cross a bridge structure, this is 
 frequently accomplished in creosoted wood duct. Occasionally, 
 however, iron pipes are used to conduct cables across a steel bridge, 
 
DESIGN, CONSTRUCTION, OPERATION, ETC. 67 
 
 but where this is done, these pipes are supported so that they are 
 insulated from the metal work of the bridge. 
 
 2. Conduit Construction. 
 
 Cable sheaths cannot be said to be insulated from earth even 
 when installed in non-conducting duct material, but as compared 
 with pipes which are laid directly in the earth, their resistance 
 to ground is generally very high. Unless surrounded with mud or 
 water, cable sheaths usually make a line contact with the duct 
 walls, whereas pipes make a surface contact of much greater area. 
 
 The study of the insulation of cable sheaths from earth there- 
 fore resolves itself into a study of suitable conduit construction 
 methods since experience has demonstrated the failure of any sort 
 of wrappings, dips, or coatings to afford protection of any value 
 from electrolysis. Indeed, wrappings, dips, and coatings have 
 been shown to be distinctly harmful where pipes or cables are 
 positive to the earth since they tend to localize the discharge of 
 current and thus to accelerate failures. 
 
 (a) Signal Cables. The experience of the Bell Telephone 
 System has demonstrated that multiple and single vitrified clay 
 duct and creosoted wood duct are all equally good as duct material 
 from the standpoint of electrolysis, their choice in specific cases 
 being a question of supply and cost. Iron pipe is occasionally 
 used, but, due to its cost, only when necessary in avoiding 
 obstructions. 
 
 When iron pipe is used, it is so laid that there will be no contact 
 between it and the trolley rails, steel bridges, water pipes, gas 
 pipes or other underground structures or the metal work of build- 
 ings. When iron pipes must be laid as conduit so close to rails 
 or other grounded metallic structures that a separation of at 
 least one foot of earth cannot be obtained, the pipes are separated 
 from the rails or other grounded metallic structures by a layer of 
 concrete or creosoted plank Three inch, vitrified sewer tile with 
 cement joints is now being commonly used for laterals to poles or 
 building connections. 
 
 In good conduit construction the necessity is recognized of 
 rendering the joints between lengths of duct material, sufficiently 
 tight to prevent the infiltration of dirt and silt and also to maintain 
 a sufficient slope to the conduit to insure good drainage toward 
 manholes, the manholes in turn being drained by sewer connections 
 or to sumps. Particular care is exercised to prevent dips or 
 pockets in conduit runs where moisture might collect. It is the 
 
68 DESIGN, CONSTRUCTION, OPERATION, ETC. 
 
 practice to rack cables in manholes, a free space of twelve inches 
 being maintained between the lowest cable and the manhole 
 floor. The cables are in metallic contact with the metal hanger 
 which, in turn, may be in contact with or built into the manhole 
 wall, experience having indicated that no appreciable increase in 
 cable resistance to earth is obtained by insulating the cables at 
 these points with porcelain or other insulating material. 
 
 Where lateral cables enter buildings, it is the usual practice 
 in the Bell System to avoid all contact between the cable and the 
 metal structures of buildings, and wherever this is impracticable, 
 the continuity of sheaths on the entering cables is broken by an 
 insulating joint. 
 
 Occasionally conduit runs must be built through swampy 
 ground or along sections of the coast where the conduit is per- 
 manently below sea level. Where such conditions are encountered, 
 no method is practically possible for insulating cable sheaths from 
 earth and such insulation is not attempted. Such locations are 
 frequently extremely troublesome from the electrolysis standpoint, 
 and therefore special precautions have to be taken. 
 
 (b) Power Cables. The practice in conduit construction for 
 light and power cables is somewhat different from that used for 
 signal cables because the former are characterized by necessity 
 of providing for troubles originating within the cables and for 
 the dissipation of the heat losses of the cable. The most common 
 types of duct material used are single duct vitrified tile, multiple 
 duct vitrified tile, fibre conduit and stone conduit. Iron pipe is 
 frequently used for short laterals to buildings and for cable pole 
 connections, and occasionally where on account of lack of space 
 other types cannot be installed. It is a common practice to in- 
 stall a 3-inch concrete envelope entirely surrounding all types of 
 power conduits. Multiple conduit made up of single duct tile 
 is laid with staggered joints and in the case of the fibre and stone 
 conduit, the ducts are separated by an inch or more of concrete. 
 Fibre duct is generally considered as a mold for the concrete which 
 latter is depended upon for strength and for the separation of the 
 cables in the several ducts. 
 
 The waterproofing of underground conduits for" the purpose of 
 excluding moisture and improving the conditions regarding elec- 
 trolysis was tried a number of years ago, but it was very expensive 
 and found to be quite useless unless the manholes also could 
 be waterproofed, and this did not appear to be practicable. 
 
 The report? of the effect of the different types of duct on elec- 
 
DESIGN, CONSTRUCTION, OPERATION, ETC. 69 
 
 trolysis conditions vary considerably, but this is probably due to 
 the nature of the soil in which the conduits are located, the amount 
 of moisture in the soil and the character of the paving under 
 which the conduits are installed. In those locations where 
 the conduit is located in flat country with poor drainage and with 
 the natural water level only slightly below the level of the con- 
 duits, the effect of the dirt and moisture in the ducts and the 
 dampness in the surrounding earth is to lower the resistance of 
 the cables to earth so that this value is not materially greater 
 than it would be if they were installed directly in the earth. In 
 other locations where the surface of the ground is hilly or suffi- 
 ciently undulating to afford good drainage facilities, the cables 
 installed in ducts with a concrete envelope are fairly well insulated 
 from the earth. 
 
 Although iron pipe is not generally used in line conduits, it is 
 frequently necessary to employ it for laterals from manholes to 
 poles and buildings, in order to avoid obstructions or to comply 
 with requirements. If used as conduits for drained cable sys- 
 tems, iron laterals will increase the danger to gas and water ser- 
 vice pipes which they cross. They also lower the resistance be- 
 tween the earth and cable sheaths which they contain and there- 
 by enable the cables to pick up larger amounts of stray current 
 than they otherwise would. 
 
 In order to afford the return current a metallic path to the 
 station in case of the failure of the cable, it is the standard practice 
 with many companies to connect the lead sheaths of all of their 
 cables in every manhole. This serves also to prevent serious 
 differences in potential between the lead sheaths of cables in the 
 same conduit at the time of a burnout and the resulting damage 
 to lead sheaths in adjacent ducts which would otherwise occur. 
 
 Where metal cable racks are used in manholes it is a frequent 
 practice to insulate the cables from such racks, this being done 
 to prevent damage from electrolysis as well as to prevent damage 
 in case of a burnout of one of the adjacent cables. 
 
 Unless necessary as a protective measure for isolated sections, 
 cable sheaths should not be artificially grounded. Grounds in 
 negative areas through which stray current might be picked up 
 should be avoided wherever practicable. 
 3. Surface Insulation. 
 
 In the early days of the use of lead covered cables for light 
 and power in this country, it was customary to have the lead 
 covered cables incased in a wrapping of jute saturated with a pre- 
 
70 DESIGN, CONSTRUCTION, OPERATION, ETC, 
 
 servative compound with the idea of preventing damage to the 
 cables by electrolysis. While this may have been fairly satis- 
 factory as a temporary expedient, the preservative compound in 
 the course of time would gradually disappear and the rotting of 
 the jute would follow. In pulling such cables out of the ducts, it 
 was found in some cases that the jute was so badly rotted that 
 it could not be left on the cables when they were reinstalled in 
 another location, and in other cases, the jute would adhere to 
 the ducts or become caught on the edges of the ducts and form a 
 very serious obstacle to the removal of the cable. Moreover, 
 coatings of this character are not always a protection against 
 electrolysis and may even accelerate it by localizing the corrosion, 
 as explained in the discussion of surface- insulation for pipes. On 
 account of these difficulties, the use of the jute covering on the 
 lead covered underground cables was generally abandoned some 
 years ago. 
 
 4. Insulating Joints. 
 
 Some light and power companies have used insulating joints 
 for protecting their cables from electrolysis. In some cases each 
 section was connected to a ground pipe or plate under the floor 
 of the manhole. If the conditions were favorable for electrolytic 
 action, these ground plates or pipes served merely as auxiliary 
 anodes and would be destroyed by electrolytic action in the course 
 of a few years, thus rendering them ineffective except at a con- 
 siderable annual expense for maintenance. Partly for this reason, 
 but more because of the general adoption of cable drainage as a 
 method of electrolysis mitigation, the use of insulating joints 
 for protecting lead covered cables for light and power purposes 
 has been practically abandoned in this country. 
 
 As the drainage of cables requires continuous lead sheaths, 
 insulating joints are not now ordinarily used in cable systems. 
 With drainage it is also desirable that the several cables in any 
 duct system be bonded together in the manholes so that all cables 
 may be equally drained and also that in case of a failure of one 
 cable the current through the fault to the sheath can find a con- 
 tinuous metallic return path to the station. If the insulation 
 fails on a cable with an isolated lead sheath, the potential of the 
 sheath will become approximately that of the conductor and 
 destructive arcing may occur at the insulating joints, and in addi- 
 tion, holes will be burned in the lead sheaths of the cable where 
 it is in accidental contact with other cables or where it rests on 
 
DESIGN, CONSTRUCTION, OPERATION, ETC. 71 
 
 metal cable racks or supports in manholes. Where insulating 
 joints are used, it is therefore quite necessary to ground each section 
 of the sheath. 
 
 Under special conditions insulating joints can sometimes be 
 used to advantage in protecting cables from electrolysis, as for 
 example, when the cables are remote from any railway tracks or 
 negative return circuit to which they can be drained, or where a 
 cable system which is not drained can be prevented from collecting 
 stray current at points of intersection with railway tracks by 
 their use. Fig. 17 shows the type of insulating joint used by 
 several large electric power companies in the sheaths of trans- 
 mission cables which are not protected by drainage. 
 
 Another situation sometimes requiring insulating joints in 
 order to prevent cables from picking up excessive current, or to 
 prevent arcing, is to be found where they make contact with a 
 steel bridge or are otherwise brought into intimate contact with 
 the earth. Under such conditions the section making contact can 
 be isolated by the use of insulating joints and continuity of the 
 system maintained by bonding around the section so isolated. 
 Such conditions as these, however, are comparatively rare. 
 
 Insulating joints in lead sheaths are not only expensive but 
 represent points of discontinuity which may give rise to various 
 troubles and are usually avoided in practice except under such 
 unusual conditions as are here mentioned. 
 
 C. PIPE SYSTEMS 
 
 1. Surface Insulation. 
 
 In the cities where there is trouble from electrolysis, the service 
 pipes of the gas and water companies are more subject to failure 
 than the cast iron mains as the walls of the wrought iron pipes 
 are much thinner. Also, in the electrolytic corrosion of cast 
 iron pipe a graphitic residue remains intact and has a strength 
 sufficient to withstand gas pressure and in some cases even low 
 water pressure, while with wrought iron or steel the metal is 
 corroded away without leaving such a residue. For these reasons 
 some gas companies have made it a practice to apply a surface 
 covering to their service pipes. This covering is generally similar 
 to that described above for lead covered cables, but it sometimes 
 consists of several layers of jute, burlap, cheese cloth, or paper, each 
 of which has an application of insulating preservative compound 
 before applying the next layer. Such insulating coverings have 
 been more successfully applied to services than to lead covered 
 
72 
 
 DESIGN, CONSTRUCTION, OPERATION, ETC. 
 
 
 "5-8 
 
DESIGN, CONSTRUCTION, OPERATION, ETC. 73 
 
 cables. The expense of this covering usually precludes its use for 
 cast iron mains, although it is sometimes applied to wrought iron 
 or steel gas mains. 
 
 The principal difficulty in coatings applied to pipes or lead 
 cable sheaths is that the coatings are not continuous and that in 
 spite of all efforts for their prevention minute holes or pores will 
 exist in such coatings. Through these minute pores the electrolyte 
 will ultimately penetrate and electrolytic action will result. As 
 the amount of pipe or cable surface exposed through these pores 
 is small, the action will be very slow at the start and it may be quite 
 imperceptible for a number of months. In the course of time, 
 however, if the conditions are favorable for electrolysis, an oxide 
 of the metal will be formed opposite the pores and as the oxide 
 occupies more space than the metal, the coating will be lifted from 
 the metal, thus rapidly increasing the area of metal exposed to 
 the electrolytic action. As this action is concentrated at a com- 
 paratively few points by the coating, the result is that the destruc- 
 tion of the pipe or cable may occur more rapidly, due to this 
 intensified local action, than would occur if the pipe or cable was 
 without such coatings so that the action would be distributed 
 over the entire area of pipe or cable. 
 
 Surface insulation for the protection of pipes and cables against 
 soil or salt water corrosion is often effective, but as described 
 above, these coatings gradually deteriorate when subjected to 
 any appreciable potential difference. 
 
 Thick coatings in the form of pitch or parolite poured into a 
 containing box built around the pipe, have been used successfully 
 in special cases. The box should be quite strong so as not to sag 
 beneath the weight of the insulating material while pouring or 
 after back-filling. The pipe should be supported in this box by 
 means of blocks of glass or of pitch impregnated wood, so as to 
 prevent its exposure in the event of the cold-flow of the insulating 
 material. In pouring, extreme care must be exercised to prevent 
 particles of earth or stone from getting into the box, and the 
 insulating material should be hot enough to flow freely without 
 boiling or bubbling. If it is too hot, the boiling or bubbling will 
 result in air holes when the material solidifies, and these air holes 
 may admit moisture to the pipe. If the pipe to be covered is 
 laid on a grade, or if it is more than 25 feet long, it will be neces- 
 sary to pour the material in sections, using dams made of pitch 
 impregnated wood to retain the molten material. The material 
 should cover the pipe to a depth of about two inches and a rigid 
 
74 DESIGN, CONSTRUCTION, OPERATION, ETC. 
 
 cover should be placed on top of the box or trough to prevent 
 stones or earth from working their way through the insulating 
 material. This boxing method is also applicable to service or 
 other small pipes, and while somewhat more expensive, it is pre- 
 ferable to the wrapping method because in its application there 
 are fewer chances of imperfections escaping detection. 
 
 Too much care cannot be exercised in applying insulating cover- 
 ings in regions where there is a strong tendency for current to 
 leave the pipe. A single imperfection through which moisture 
 can reach the pipe will cause it to be destroyed more rapidly with 
 the covering than without it. As an additional precaution where 
 insulating covering is applied in a positive area, insulating joints 
 are often installed in the pipe at each end of the covering. If 
 the covered section is more than 2,000 feet long, additional in- 
 sulating joints should be installed at intermediate points. 
 
 The application of insulating covering is not always limited 
 to the positive areas in which current tends to leave the pipe. 
 They are quite often used to prevent current reaching the pipe, 
 in negative areas, where a pipe crosses or comes near to a 
 trolley line or other underground metallic structures to which it is 
 highly negative. 
 
 The costs of installing insulating coverings of the character 
 referred to will vary over fairly wide limits, depending upon 
 the size of the pipe, the length to be covered, the character of 
 the soil, and the depth of the pipe, etc. In 1915 the cost of 
 boxing and covering 500 feet or more of 8-inch line laid at a 
 depth of about 30 inches in ordinary soil averaged about one 
 dollar per foot. In 1919 this figure had increased to about three 
 dollars per foot. 
 
 2. Insulating Joints. 
 
 (a) New Work. The value of insulating joints in pipes as a 
 means of preventing or reducing electrolysis has long been recog- 
 nized, but the manner of employing them has not always been 
 such as to accomplish the desired end. Their effectiveness will 
 depend very largely upon the frequency with which they are 
 installed in any pipe line and somewhat upon other factors, such as 
 the resistivity of the soil, the magnitude of the potential gradient 
 in the earth and the degree of isolation maintained with respect 
 to other underground structures. 
 
 Current flow on metallic pipe lines can be practically prevented 
 by using a sufficient number of insulating joints. A pipe line 
 
DESIGN, CONSTRUCTION, OPERATION, ETC. 
 
 75 
 
 r 
 
 i 
 
 s 
 
 cr- 
 
 I 
 
 1i 
 
 13 
 
 J 
 I 51 
 
 I Q>J* 
 
 s *: + 
 
 2 0) 
 
 o o5 
 
 <J/ ^ CO 
 
 (8 
 
 c 
 
 ^ s 
 
 CP^fe 
 
 "E <n 
 CD o 
 
 li 
 
 
 v z 
 
 O P 
 
 - J^ 
 
 81 
 
76 DESIGN, CONSTRUCTION, OPERATION, ETC. 
 
 laid with every joint an insulating joint has a comparatively 
 high resistance, and no substantial current can flow on such a 
 line. 
 
 It is sometimes possible to break up the electrical continuity 
 of the line and substantially protect it from electrolysis by the 
 use of a comparatively few insulating joints, but in these cases 
 tests should be made to see that the longitudinal flow of current 
 along the pipe has been practically eliminated. 
 
 The services can be prevented from making electrical contact 
 with other systems by the use of insulating joints within the 
 premises served, as shown in Fig. 18. Without the insulating 
 joint in the service pipe, stray current could enter from the other 
 piping system and injure both the service and the section of main 
 to which it connects. 
 
 Some gas companies, principally natural gas companies, have 
 established the practice in all new work of insulating services at 
 the meter connections within the premises, thus preventing the 
 flow of current between gas and water services. If this is generally 
 applied on new mains of considerable length, it is also advisable 
 to install insulating joints at selected locations on the main. 
 
 (b) Cement Joints. Cement joints have long been used on 
 gas mains and have been found to preserve a high resistance over 
 a long period of time, and if used in sufficient numbers they are 
 effective in preventing the flow of stray current on pipe lines. 
 The standard cast iron bell has been used successfully with 
 cement joints on small mains but some gas companies have had 
 difficulty in using cement on mains 12 inches in diameter or larger. 
 Cast iron pipe is now being manufactured with the bells especially 
 designed for cement joints so that they can be used on large size 
 mains. This joint, illustrated in Fig. 19, is known as the type B 
 joint, as covered by the specifications of the Committee on Cast 
 Iron Pipe Joints of the American Gas Association. The calking 
 recess is unusually long and has a slight taper whereby the joints 
 are tightened when the pipe line contracts. When properly made, 
 these joints have a mechanical strength considerably in excess of 
 the pipe itself. 
 
 (c) Leadite and Metallium. Other substitutes for lead, such as 
 "Leadite" and "Metallium" are being used on water mains. 
 Some years ago the Bureau of Standards made tests on "Leadite" 
 joints and found this material when new to have a very high 
 electrical resistance, comparable with that of cement, but after 
 several years in service to decrease in resistance to only a very 
 
DESIGN, CONSTRUCTION, OPERATION, ETC. 
 
 77 
 
 b, 
 
 TJ * ; c 
 
 C ^ 5 00 
 * O -o "** 
 
 v r 
 
 S?vi> 
 
 Sfl^ 
 :!- 2 ^i 
 
 ^li if I' 
 
 it II ti. 
 x > 
 
 IlKfi- 
 
 s!l?:D2 -oonr- 
 
 g 
 
 U 
 
 oS 
 
 - aj . v, 
 
 31 6x 
 
 ** 
 
 l^ 1 'O*G'-* 
 OO'-'JrJ'CO 
 
 '- 
 
 ioooC'r'aj'Oo 
 <N cc 
 
 8 2 2 S 8 S 3 g 
 
 CD^COCOO^Ot^t^^^l^^ 
 
 H 
 
 P-l (XQ 
 
 1 
 
 ! 
 
 o 
 
 g, 
 
 _) 
 
 8 
 
 C^J C^l IN C^l N 
 
 OOOOOOO-}OOO 
 
 o.o>-NTjeooot*a>oio 
 
 * * S 2 & S S s Js 3 g 
 
 * 
 
78 DESIGN, CONSTRUCTION, OPERATION, ETC. 
 
 mall fraction of the original value. The change was attributed 
 to the slow oxidation of the sulphur contained in the compound, 
 resulting in the production of sulphuric acid. No corresponding 
 data are yet available on "Metallium." 
 
 (d) Dresser Couplings of the ordinary type which have been 
 extensively used on wrought iron and steel gas mains are uncertain 
 and variable in their resistance, depending upon the manner in 
 which they are installed. However, if used throughout any pipe 
 line their average resistance is so high as to practically eliminate 
 the flow of stray current. 
 
 (e) Special Insulating Joints. A special high resistance joint 
 is made, known as the "Dresser Insulating Coupling," and is 
 used to prevent the flow of stray current on pipes. Insulating 
 joints, such as wood stave joints, and flange joints with insulated 
 bolts and gaskets of insulating material are sometimes used on 
 large mains at river crossings or at points of intersection with 
 street railways and at other special locations. The effective length 
 of such joints can be increased by thoroughly insulating the pipe 
 with wrappings or covering for some distance on either side of the 
 joint. This treatment is often applied to important oil and high 
 pressure gas pipe lines. 
 
 (f) Insulating Joints Applied to Kxisting Pipe Lines. Pipe 
 lines acting as ties between two extensive systems or networks 
 sometimes carry considerable current from one system to the other 
 and this can be reduced or practically eliminated by the use of 
 comparatively few insulating joints installed in the main con- 
 necting the two systems. To distribute the stray current around 
 insulating joints so installed, the joint can either be made long or 
 the pipe insulated for some distance on either side. 
 
 A large industrial plant or a small community may be supplied 
 with gas or water through a single pipe over which stray current 
 may flow and cause damage at some point which would otherwise 
 not be in danger. The use of one or more insulating joints will 
 often correct such a condition at little expense. 
 
 A pipe line crossing under an electric railway track or through 
 a river or wet ground can be prevented from discharging or 
 collecting current at such points by the use of insulating joints 
 on both sides of the exposure. 
 
 Service pipes which are subject to corrosion at points where 
 they cross under railway tracks are often insulated from the mains 
 by the use of insulating joints at times of replacements thus pre- 
 
DESIGN, CONSTRUCTION, OPERATION, ETC. 79 
 
 venting the further passage of current from the main to the 
 service. 
 
 Insulating joints are also frequently used to prevent the inter- 
 change of current between two piping systems, as shown in Fig. 
 18, or between a piping system and a cable system or other under- 
 ground structures. In order to protect gas services or water 
 services where they cross under tracks, it is often necessary to 
 install insulating joints both at the main and within the premises 
 to prevent the flow of current from services of another system to 
 which they may connect. This condition exists where gas water 
 heaters are in use as these appliances usually make a firm metallic 
 contact between the gas and water services. In Fig. 20, if the 
 gas and water mains are both positive to the track, accelerated 
 corrosion will take place on the services where they cross under 
 the track. To protect one service without regard to the other, it 
 is obviously necessary to install insulating joints at A and B, or 
 C and D. 
 
 Insulating joints have been installed at selected locations by 
 some gas and water companies as an auxiliary to a negative feeder 
 system. For example in Providence, Rhode Island, after an 
 insulated negative feeder system was put in operation insulating 
 joints were installed on gas and water mains to still further reduce 
 the stray current on the pipes. 
 
 The cost of installing insulating joints when pipes are uncovered 
 for repair or replacement is comparatively a small item, and often 
 affords a satisfactory means of preventing further damage to 
 them. 
 
 3. Shielding. 
 
 In special cases underground structures have been protected 
 from electrolysis by connecting to the structure an auxiliary 
 metallic conductor located so as to cause the current to flow to 
 earth from the auxiliary conductor. This mode of protection is 
 known as shielding. The method has in some cases been applied 
 to the dead end of an underground metallic structure which is 
 highly positive to earth. In such cases an auxiliary shielding 
 plate or pipe of adequate ground contact surface extending beyond 
 the dead end and electrically connected to the structure to be 
 protected has been installed in such a manner that the bulk of the 
 current was caused to leave the auxiliary shielding conductor, thus 
 affording a certain degree of protection to the dead end of the 
 structure. One application of this method, which is in use, is 
 
80 
 
 DESIGN, CONSTRUCTION, OPERATION, ETC. 
 
 
 
 
 * I 
 
 
 
 
 1 I 
 
 * i 
 
 c 
 
 1 
 
 
 -2 2 
 
 (0 ,S _c 
 
 >N^ T 
 
 
 
 
 <3 i 
 
 5 
 
 
 8 
 
 
 
 
 "5 
 
 
 
 "*" = 5 
 
 
 
 
 
 S 
 
 ( 
 
 1 i 
 
 - 
 
 LJ 0) V 
 
 cfr- 
 
 
 
 
 
 
 
 mm 
 
 
 
 "2 
 . ^ x 
 
 
 
 
 
 
 * 
 
 
 
 ^ i, c 
 
 
 
 
 I 
 
 MMHM 
 
 i 
 
 
 
 ? CO 
 
 
 
 
 
 
 
 
 
 fc to T 
 
 
 
 
 
 
 
 
 
 r g * 
 
 
 
 
 
 
 
 
 1 ( 
 
 
 t c (U O 
 
 
 
 
 
 
 
 
 
 co v ~f 
 
 
 II 
 
 
 u 
 
 
 Q 
 
 \ 
 
 'x 
 
 / \ (^ "T* 
 
 * * 
 Ifcl 
 
 1 
 
 
 
 . 
 
 - 
 
 
 
 ^$ 
 
 
 
 
 
 
 
 
 
 ^J (1) W 
 
 ^ 5- - 
 
 
 E 
 
 
 ( 
 
 \ ( 
 
 t 
 
 
 3 I 
 
 I 8 
 
 
 
 
 
 
 
 
 
 <o Jj 
 
 o 
 
 
 
 
 
 
 4 
 
 t 
 
 
 oo df 
 
 
 
 
 
 
 
 
 
 a >^ 
 
 W:| 
 
 
 
 
 
 
 1 ( 
 
 i I 
 
 
 i aJ .? 
 
 
 
 
 
 
 
 
 
 
 CO i. 
 
 
 
 
 
 
 
 
 
 "If 
 
 <D * = 
 
 
 
 
 
 * 
 
 
 ^g^u] J3 
 
 
 
 
 
 
 1 
 
 li^ 
 
 > K 4- C 
 
 
 
 
 ?r?^ i 
 
 12 
 
DESIGN, CONSTRUCTION, OPERATION, ETC. 81 
 
 that of a service pipe crossing under tracks or crossing other 
 structures to which it is positive and where the pipe comes rela- 
 tively close to the rails or other structures at the point of crossing. 
 In these cases a larger shielding pipe, usually of heavy cast iron, 
 has been placed around the service pipe and electrically connected 
 to the service pipe and extended sufficiently on each side of the 
 crossing so that the major part of the current was caused to leave 
 the shielding pipe, thereby corroding the latter while protecting 
 the service pipe. 
 
 It is very important that a thorough metallic connection be 
 made between the pipe to be protected and the shielding pipe. 
 Otherwise, the service pipe is likely to corrode where current 
 leaves it to flow through earth to the shielding pipe. Unless the 
 shield is in the form of a pipe completely surrounding the structure 
 to be protected, this method of protection is uncertain and should 
 be used only in very special cases. When applying this method it 
 has been found necessary to take care that the auxiliary shielding 
 conductor does not merely increase the electrode area from which 
 the current leaves, because in this case the current will continue 
 to leave from the structure which is to be protected unless an 
 insulating covering is applied to the pipe beyond the protecting 
 shield. This has been found to be the practical result where a 
 shielding conductor of the same or less contact area was placed 
 in the earth near the structure to be protected and where the stray 
 current has left both structures. 
 
 III. MEASURES INVOLVING INTER-CONNEC- 
 TION OF AFFECTED STRUCTURES AND 
 RAILWAY RETURN CIRCUIT 
 
 A. ELECTRICAL DRAINAGE OF CABLE AND PIPE SYSTEMS 
 
 Electrical drainage consists in connecting the affected structure 
 to the railway return circuit by insulated conductors in such a 
 manner that the current leaves the structure through these 
 connections instead of flowing to earth. This prevents corrosion 
 in the neighborhood of the drainage connections, but increases 
 the current flowing on the structure and the voltage drop along it, 
 which latter results are generally undesirable for reasons discussed 
 in detail in subsequent paragraphs. 
 
 Drainage connections are usually made by running copper 
 cables either to the busbar of the railway supply station or to 
 negative return feeders. Connections to tracks should be avoided 
 
82 DESIGN, CONSTRUCTION, OPERATION, ETC. 
 
 because the failure of rail bonds might cause dangerous currents 
 to flow over the drainage connection and also because of the pos- 
 sibility of getting a current reversal, particularly when the adjacent 
 substation shuts down during the light load period. However, 
 when insulated negative feeders are used, the drainage connections 
 may be made to the rail terminals of the feeders. Connections 
 to rails are sometimes installed where a conduit line or a pipe 
 crosses a railway track at a considerable distance from the power 
 supply station and other means of draining would be awkward 
 and expensive, but they should be made with considerable dis- 
 cretion and should be carefully recorded and regularly inspected. 
 
 Where used, drainage should be reduced to a minimum con- 
 sistent with the protection of the drained structure in order to 
 reduce the hazard to other adjacent underground systems. 
 
 The drainage of one system tends to establish differences of 
 potential between the various underground systems, resulting in 
 interchange of current with consequent injury to the system at 
 the higher potential. In order to avoid this condition, it is de- 
 sirable to interconnect the various systems and drain them over 
 common conductors. As structures owned by different interests 
 cannot be bonded together except by an agreement between the 
 owners this has frequently of itself made it impossible to apply a 
 comprehensive drainage system to all structures because of the 
 impossibility of obtaining an agreement of all owners to allow 
 connections to their structures, except on condition that other 
 interests assume liability for any injury which may result from 
 such interconnections. 
 
 If, however, the foregoing method of unified drainage is carried 
 out so that the drained structures are at all times negative to 
 earth, no electrolytic corrosion of such structures will result. 
 Just how difficult it may be to maintain pipes negative to earth 
 at all points and at all times by means of drainage is a question 
 which cannot be answered until investigations have been carried 
 further. 
 
 The objections to electrical drainage apply most forcibly to 
 pipe networks, particularly to gas and oil pipes on account of the 
 inflammable substances carried. Drainage should be considered 
 only as a supplementary measure to the improvement of the rail- 
 way return circuit or as a temporary measure in cases where acute 
 electrolytic corrosion has resulted. It can never take the place 
 of an adequate railway return circuit. 
 
 Notwithstanding its numerous disadvantages and limitations, 
 
DESIGN, CONSTRUCTION, OPERATION, ETC. 83 
 
 there are engineers who believe that pipe drainage has a definite 
 field of usefulness. The Committee, through its Research Sub- 
 Committee, is still actively engaged in investigating the magni- 
 tude and importance of the technical factors involved and until 
 further information shall have been acquired, the Committee will 
 not be in a position to reach a conclusion on this subject. 
 1. Drainage of Cable Sheaths. 
 
 (a) Method of Draining Cable Sheaths. In order to afford com- 
 plete protection to cable systems, it has been found that they 
 should be interconnected and have drainage conductors of sufficient 
 conductivity located so that the lead sheath of the cable network 
 is everywhere lower in potential than the adjacent earth. Cable 
 systems are usually installed in vitrified clay, creosoted wood, 
 or fibre ducts, and if kept free from water, the tendency to collect 
 current is much less than if they were in direct contact with the 
 earth. Owing to the higher resistance thus introduced between 
 cables and earth and the continuous character of the cable sheaths, 
 it is usually possible to lower the potential of the system below 
 that of the adjacent earth in all localities by draining relatively 
 small currents at one or more points. 
 
 In order to prevent the interchange of current through earth 
 between the several cable sheaths in any conduit system, it is 
 necessary to bond the sheaths together at frequent intervals. 
 Some companies make a practice of bonding at every manhole 
 and good practice requires such bonding at intervals not to exceed 
 five hundred feet. Bonding is usually accomplished by sweating 
 a flat copper strip or a copper cable to all cables within any system 
 which may properly be bonded together. Foreign cables which 
 enter any duct system are also bonded to the system they parallel. 
 It is often necessary to interconnect signal cables with lighting and 
 power cables so as to avoid differences of potential which might 
 otherwise occur, but where this is done, a fuse should be installed 
 in the bond connection to the signal cable so as to eliminate the 
 possibility of high voltage current getting on the signal cable 
 sheaths. 
 
 It is desirable to provide means for measuring all drainage 
 currents and where the drainage feeder is extended to the supply 
 station, an ammeter or shunt is usually installed for that purpose 
 within the station. Where the drainage cable does not enter the 
 supply station, measurement can be made within a manhole or on 
 a pole, or wherever the drainage cable is accessible. 
 
 Where a cable system tends to become positive in regions remote 
 
84 DESIGN, CONSTRUCTION, OPERATION, ETC. 
 
 from the railway supply station, it is necessary either to use a 
 long copper cable for drainage at a considerable expense or to 
 resort to some other method of protection. Aerial telephone 
 cables are sometimes used for this purpose, but are not employed 
 except when other conductors are not available or would be unduly 
 expensive. 
 
 Cables are sometimes found to be positive only during certain 
 periods of the day or their potential may reverse from time to 
 time due to fluctuations in the railway load. Where this condition 
 is considered dangerous from the electrolysis standpoint an 
 automatic switch is sometimes installed which is closed during the 
 period the cable is positive and automatically opens when the 
 cable becomes negative, the object being to prevent the cable 
 from taking on current while in a negative condition. The cost 
 of automatic switches and the fact that they add an objectionable 
 complication to the plant are reasons why their use should be 
 restricted as much as possible. 
 
 Automatic or manually operated switches should be provided 
 in all drainage cables terminating in railway supply stations in 
 order that they may be opened during the period when the station 
 is not in operation. Automatic substations which start and stop 
 without attendants should be provided with facilities for accom- 
 plishing this result. 
 
 (b) Heating Effect of Stray Current on Cable Sheaths. Stray 
 current on the sheaths of lead covered cables causes a heating 
 effect which impairs the carrying capacity of power cables. In 
 some cases this effect may be objectionable. 
 
 The following formulae have been developed for single conduc- 
 tor and three conductor cables to give their current carrying 
 capacity when sheath currents flow. The values obtained give 
 the conductor the same temperature rise above surrounding 
 structures as produced by their normal current when no sheath 
 currents are present. 
 
 The formulae have been developed on the following basis: 
 
 1. That the watts dissipated in the sheath are effective in 
 raising the sheath temperature but that they do not affect the 
 rise of the conductor over the sheath. 
 
 2. Resistivity of lead 12 times that of copper. This assump- 
 tion, while not strictly correct, will give results within an accuracy 
 obtained by considering other factors as constants, such as the 
 radiation constants of the lead sheath. 
 
DESIGN, CONSTRUCTION, OPERATION, ETC. 85 
 
 Definitions 
 
 A = temperature rise of conductor over sheath for a given con- 
 ductor current. 
 
 B = temperature rise of sheath over cable surroundings for the 
 same conductor current as for A . 
 
 C = temperature rise of conductor over cable surroundings for 
 the same conductor current as for A and B. 
 
 D outer diameter of lead sheath in inches. 
 d = inner diameter of lead sheath in inches. 
 
 r ! . , area in circular mils 
 
 a = area or conductor in circular inches = 
 
 l,UUU,Uu(J 
 
 I s = amperes flowing in sheath. 
 
 7 = normal current rating of cable. 
 
 X = defined as 
 
 I'o 
 
 I = conductor current with (XI ) sheath currents. 
 
 For Single Conductor Cable 
 
 12a 
 
 For Three Conductor Cables 
 
 /= T _,, 4aX 2 B 
 
 (D*-d*) (A + B) 
 The values of A, B, and C can be found for single and three 
 conductor cables by referring to Atkinson's article on "Carrying 
 Capacity of Cables" in the September, 1920, issue of the Journal 
 of the A. I. E. E. 
 
 Examples 
 
 1. Single conductor cable, 250,000 C. M., 1/8 inch lead sheath, 
 4/32 inch paper insulation. Normal current 510 amperes. What 
 is resultant carrying capacity with 100 amperes sheath current? 
 
 = = . 196, X* = . 0384. a = .250, = = .735. 
 
 olU L> Zo .U 
 
 D = 1 .09, d = .84, D 2 - d? = .484. 
 
 Resultant carrying capacity=510yi- !!LMLL^ 
 510 (.91) = 463 amperes. 
 
 2. Round Three Conductor No. 4/0, paper insulation, 
 
86 DESIGN, CONSTRUCTION, OPERATION, ETC. 
 
 1/8 inch lead sheath. Normal current 242 amperes. What is 
 resultant carrying capacity with 200 amperes sheath current ? 
 
 D = 2 .61, d = 2 .36, D 2 - d 2 = 1 .25. 
 
 ., 0/lo /, 4 (.2116) (.684) (.43) 
 Resultant carrying capacity = 242 -u 1 -- ^ -' = 
 
 .893 (242) = 216 amperes. 
 
 In a similar way the reduction of current carrying capacity for 
 certain cables has been calculated in Tables 1 to 4. Tables 
 1,2, and 3 are for single conductor cables for 250 volt, 2,300 volt, 
 and 600 volt service, respectively. Table 4 is for 13,200 volt, 
 3 conductor cables. 
 
 The normal ampere rating in the second column of Tables 1 
 and 2 for rubber insulation is based on the following formula. 
 
 Wherein the following terms are used : 
 di = diameter of copper in inches. 
 d z = diameter over insulation in inches. 
 dz = diameter over sheath in inches. 
 K = resistivity of insulation in degrees C. rise per watt per 
 
 inch cube. 
 
 J = radiation resistivity of lead sheath to ambient sur- 
 roundings in degrees C. rise per watt per inch square. 
 r = resistance of conductor at 7\, per inch length. 
 / = current carrying capacity of cable. 
 T l = permissible copper temperature, in degrees C. 
 T 2 = temperature of ambient surroundings in degrees C. 
 In solving the formula, the following values of the several con- 
 stants were taken : . 
 
 K = 300C. rise per watt per inch cube. 
 J = 200C. rise per watt per inch square. 
 T 2 = 40C. 
 
 The normal ampere rating in tables 3 and 4 for paper insula- 
 tion is based on the data in the paper entitled "High-Tension, 
 Single-Conductor Cable for Polyphase Systems," by W. S. 
 Clark and G. B. Shanklin, Transactions of the A. I. E. E., 1919, 
 Vol. XXXVIII, page 917. 
 
DESIGN, CONSTRUCTION, OPERATION, ETC. 
 
 87 
 
 The conductor temperatures used are in practical agreement 
 with Rule 9100, page 95, Revision of 1921 of the Standards of the 
 American Institute of Electrical Engineers. 
 
 Where different normal ampere ratings or temperatures are 
 used, the percentages of normal current that can be carried with 
 various sheath currents will differ from those given in these tables. 
 
 Naturally, the effect of sheath currents is greater for small and 
 medium sized cables, and it may be noted that cables of these 
 sizes and types are most commonly met in complicated distribu- 
 tion networks. 
 
 Also, for the same size conductor, a given sheath current will 
 reduce the current carrying capacity of the cable to a lesser extent 
 as the insulation thickness is increased. 
 
 In cases where drainage must be employed and where heating 
 is a factor, the sheath currents can be reduced to a minimum by 
 limiting the drainage to the smallest values which will protect the 
 system. 
 
 TABLE 1. 
 
 EFFECT OF SHEATH CURRENTS ON ALLOWABLE CONDUCTOR CURRENT OF 
 SINGLE CONDUCTOR 250-VOLT 2/32" RUBBER INSULATION. SHEATH AS- 
 SUMED 1/16" THICK. 
 
 Conductor 
 size 
 
 Normal ampere 
 rating at 60 C. 
 Conductor temp. 
 40 ambient 
 
 Per cent of normal rating which can be carried with sheath 
 currents as indicated 
 
 10 amp. 
 
 20 amp. 
 
 30 amp. 
 
 40 amp. 
 
 50 amp. 
 
 No. 6.... 
 4 
 2 
 1/0*. . 
 
 56 
 
 75 
 101 
 137 
 
 96.0 
 96.8 
 97.7 
 98.3 
 
 83.0 
 86.6 
 90.2 
 93.0 
 
 54.3 
 66.0 
 76.0 
 83.0 
 
 49! 5 
 66.8 
 
 37.2 
 
 * Thickness insulation = 5 /64' 
 
 TABLE 2. 
 
 EFFECT OF SHEATH CURRENTS ON ALLOWABLE CONDUCTOR CURRENT OF 
 SINGLE CONDUCTOR 2,300-VOLT 6/32" RUBBER INSULATION. SHEATH AS- 
 SUMED 3/32" THICK. 
 
 
 Normal 
 
 
 Conductor 
 
 ampere 
 rating at 
 60C-.25E 
 
 Per cent of normal rating which can be carried with sheath 
 currents as indicated. 
 
 size 
 
 Conductor 
 
 
 
 temp. 40 
 
 
 
 
 
 
 
 
 ambient. 
 
 10 amp. 
 
 20 amp. 
 
 40 amp. 
 
 50 amp. 
 
 60 amp. 
 
 70 amp. 
 
 No. 6.... 
 
 60 
 
 99.2 
 
 96.2 
 
 90.9 
 
 82.7 
 
 71.9 
 
 55.5 
 
 23.5 
 
 4 
 
 79 
 
 99.2 
 
 96.5 
 
 92.0 
 
 85.3 
 
 75.8 
 
 62.2 
 
 34.6 
 
 2 
 
 106 
 
 99.3 
 
 97.3 
 
 93.7 
 
 88.5 
 
 81.0 
 
 71.0 
 
 57.1 
 
 1/0 
 
 139 
 
 99.4 
 
 97.6 
 
 94.4 
 
 89.5 
 
 83.0 
 
 74.3 
 
 62.6 
 
88 
 
 DESIGN, CONSTRUCTION, OPERATION, ETC. 
 
 TABLE 3. 
 
 EFFECT OF SHEATH CURRENTS ON ALLOWABLE CONDUCTOR CURRENT OF 
 SINGLE CONDUCTOR 600-VOLT 4/32" PAPER INSULATED CABLES. SHEATH 
 ASSUMED 1/8" THICK. 
 
 
 Normal 
 
 Per cent of normal rating which can be carried with sheath 
 
 Conductor 
 
 ampere 
 rating at 
 
 currents as indicated. 
 
 size 
 
 85C 
 
 
 
 Conductor 
 
 
 
 
 
 
 
 
 
 temp. 
 
 50" amp. 
 
 75 amp. 
 
 100 amp. 
 
 125 amp. 
 
 150 amp. 
 
 175 amp. 
 
 200 amp. 
 
 250.000 c.m. 
 
 510 
 
 97.8 
 
 96.4 
 
 91.0 
 
 85.5 
 
 78.3 
 
 68.7 
 
 55.7 
 
 500,000 c.m. 
 
 720 
 
 98.0 
 
 95.7 
 
 92.2 
 
 87.5 
 
 81.5 
 
 73.6 
 
 63.3 
 
 750,000 c.m. 
 
 880 
 
 98.3 
 
 96.3 
 
 93.3 
 
 89.4 
 
 84.3 
 
 77.8 
 
 69.7 
 
 1,000.000 c.m. 
 
 1,010 
 
 98.5 
 
 96.7 
 
 94.0 
 
 90.3 
 
 85.7 
 
 80.0 
 
 72.7 
 
 1,500,000 c.m. 
 
 1,250 
 
 98.8 
 
 97.2 
 
 94.5 
 
 91.8 
 
 88.0 
 
 83.3 
 
 77.5 
 
 2,000,000 c.m. 
 
 1,440 
 
 98.8 
 
 97.3 
 
 95.4 
 
 92.7 
 
 89.3 
 
 85.0 
 
 80.0 
 
 TABLE 4. 
 
 EFFECT OF SHEATH CURRENTS ON ALLOWABLE CONDUCTOR CURRENT OF 
 ROUND THREE CONDUCTOR 13,200-VOLT 6/32 BY 6/32 PAPER INSULATED 
 CABLES DUE TO STRAY CURRENTS FLOWING ON SHEATH. SHEATH AS- 
 SUMED 1/8" THICK. 
 
 Conductor 
 size 
 
 Normal 
 ampere 
 rating at 
 75 C. 
 Conductor 
 temp. 
 
 Per cent of normal rating which can be carried with sheath 
 currents as indicated 
 
 50 amp. 
 
 75 amp. 
 
 100 amp. 
 
 125 amp. 
 
 150 amp. 
 
 175 amp. 
 
 200 amp. 
 
 1/0 
 2/0 
 
 173 
 193 
 218 
 242 
 263 
 290 
 312 
 
 99.3 
 99.3 
 99. 
 99. 
 99. 
 99. 
 99. 
 
 98.4 
 98.4 
 98.5 
 98.5 
 98.6 
 98.6 
 98.7 
 
 97.3 
 97.2 
 97.3 
 97.5 
 97.6 
 97.8 
 97.7 
 
 95.6 
 95.6 
 95.5 
 95.5 
 96.2 
 96.5 
 96.4 
 
 93.5 
 93.5 
 94.0 
 94.0 
 94.4 
 95.0 
 94.8 
 
 91.2 
 91.3 
 91.8 
 91.3 
 92.3 
 93.0 
 93.0 
 
 88.3 
 88.4 
 89.1 
 89.3 
 89.8 
 90.7 
 90.6 
 
 3/0 
 
 4/0 
 250,000 c.m.. 
 300.000 c.m.. 
 350.000 c.m.. 
 
 Good duct construction with vitrified clay or fibre conduit for 
 laterals and main conduits, and the draining of manholes to 
 sewers or by sumps will tend to increase the resistance of the cables 
 to earth, and thereby reduce the tendency to collect stray currents. 
 On the other hand, thorough grounding of sheaths is in many cases 
 resorted to as a protective measure for isolated sections. 
 
 Where it is impossible to protect cable systems by natural 
 drainage, boosters have occasionally been used to artificially 
 lower the potential of the cable system. This practice, as well 
 as the over drainage of cable systems, is objectionable where 
 other underground structures are involved as it may result in 
 unusually high potential differences between the piping and 
 cable systems with resulting damage to the pipes. 
 2. Difference Between Cable Drainage and Pipe Drainage. 
 
 The early use of drainage as a method of affording protection 
 against electrolysis of lead covered cables led to the proposal to 
 
DESIGN, CONSTRUCTION, OPERATION, ETC. 89 
 
 apply the same method of protection to underground piping 
 systems. The result is that more or less pipe drainage has been 
 used, particularly on water systems and to a limited extent on 
 gas systems. While the success of protecting cable systems by 
 drainage is generally recognized, there are important differences 
 in the application of drainage to cables and to piping systems 
 which make the application of drainage to the latter difficult 
 and uncertain. Among the important differences between the 
 drainage of cable and piping systems are : 
 
 1. Cables are electrically continuous and uniform conductors, 
 while pipes are not uniform conductors and are sometimes dis- 
 continuous conductors due to the joints in them. Experience 
 indicates that in mains having cement joints a large percentage 
 of these joints are of high resistance, and in mains having lead 
 joints, occasional joints of very high resistance are found and 
 many of the joints have resistances higher than several lengths 
 of pipe. -Therefore, drainage will lower the potential of the pipe 
 for relatively short distances from the drainage taps, so that to 
 be effective a greater number of drainage taps must be installed 
 than for a cable system of the same extent. The number and 
 location of taps will depend upon the extent and physical layout 
 of the pipe network, and the expense involved will depend upon 
 the number and locations of the taps required. 
 
 2. Under certain conditions there is a tendency for current 
 flowing on a pipe to leave it on the positive side of a high resistance 
 joint, returning to the joint on the negative side, or else to flow 
 to another structure. As a result of this, joint corrosion may occur 
 at high resistance joints unless both sides of the joint are main- 
 tained negative or neutral to the adjacent earth at all points and 
 under all conditions; and conversely, no electrolytic corrosion 
 will occur on either side of a high resistance joint if the entire 
 surface of both the adjacent pipe lengths is permanently negative 
 to the surrounding earth. The difficulty of keeping a complicated 
 network of pipe negative to the adjacent earth by means of 
 drainage is much greater than in the case of cable systems. 
 
 3. Cable systems are placed in ducts with manholes conveniently 
 spaced so that the effect of the application of drainage to a cable 
 system may be adjusted so as to produce the results desired, 
 whereas with pipes buried in the ground, and in large cities 
 beneath improved pavements, it is more difficult to make the 
 necessary measurements to ascertain the effects of drainage. 
 
 4. Cables are relatively small and contained in ducts so that 
 
90 DESIGN, CONSTRUCTION, OPERATION, ETC. 
 
 unless they are in wet or marshy ground, they are but partially 
 in contact with the earth, whereas, gas or water pipes are buried 
 directly in the earth. Because of this condition, the drainage of 
 an underground piping system with, but few high resistance joints 
 results in the flow of larger amounts of current than does the 
 drainage of a cable system. 
 
 5. Currents flowing in piping systems conveying inflammable 
 substances, such as gas or oil, constitute a fire and explosion 
 hazard and many cases have been reported where stray currents 
 have caused arcs which have ignited the gas or oil when the 
 continuity of the pipe was broken. One of the objections to the 
 presence of excessive currents on gas or oil pipes is the necessity 
 for bonding around a cut in the pipe whenever a pipe is opened 
 for repairs. Under such conditions a copper wire cable is con- 
 nected around the point on the pipe to be opened. Jumper 
 cables, terminating with adjustable clamps are used by some 
 companies for this purpose. 
 
 Under certain conditions there is also danger of increasing 
 potential differences between service pipes in confined air spaces 
 which may result in causing arcs due to the intermittent contact 
 between pipes which will puncture the gas pipes and ignite the 
 escaping gas. 
 3. Application of Drainage to Pipes. 
 
 (a) Maintaining Pipes Negative to Earth. Investigations of 
 the Research Subcommittee show that when electrical drainage 
 feeders are connected to a jointed piping system the drained pipe 
 is maintained negative to the soil for only a few hundred feet from 
 the point of connection. In such cases it is necessary to extend 
 the drainage feeder along the principal pipes in the positive area, 
 which extends theoretically about 40 per cent of the distance 
 from the supply station to the end of the feeding district, and 
 connect to the pipes at frequent intervals. 
 
 (b) Effect of Pipe Drainage on Current Interchange. Various 
 conditions exist in piping systems which tend to affect the inter- 
 change of current between them, and these should be fully recog- 
 nized in the consideration or employment of pipe drainage. 
 
 If a single pipe system exists, as for example, a water system in 
 a small town, the drainage of that system will not as a rule result 
 in objectionable interchange between various parts of the network. 
 However, there are usually several piping systems present, such 
 as a lead calked water pipe system and a lead calked gas pipe sys- 
 tem. If these piping systems are not interconnected at many 
 
DESIGN, CONSTRUCTION, OPERATION, ETC. 91 
 
 points through appliances, or are not otherwise connected together, 
 the drainage of one or both systems might result in serious inter- 
 change of current. 
 
 The application of drainage to one piping system in a territory 
 where another piping system exists may result in an interchange 
 of current between the drained and undrained systems so it is 
 necessary to resort to the common drainage of all of the piping 
 systems to be protected, as the potential inequalities created by 
 separate drainage cause electrolysis at points where the current 
 leaves the undrained system to find its path to the drained system. 
 Even with the most carefully installed and maintained unified 
 system of drainage, it cannot be expected that all danger from 
 current interchange will be eliminated. 
 
 Pipe systems laid with cement joints, Dressser Joints, or other 
 high resistance joints and not interconnected with other systems, 
 will usually need no other form of protection against electrolysis. 
 If, however, such a system exists in a territory also occupied by a 
 piping system with lead calked joints and connected to it at many 
 points through applicances or otherwise, the service pipes of the 
 system with the high resistance joints and the sections of the mains 
 to which they are connected, will be electrically connected to the 
 more continuous system and so far as electrolysis is concerned 
 should be considered as a part of that system. Any electrolysis 
 condition existing on the continuous system will therefore be 
 experienced by such service pipes and the sections of the mains 
 of the discontinuous system as connect directly with it and any 
 measure which tends to protect the continuous piping system will 
 also affect the services of the discontinuous system. This con- 
 dition is illustrated in Fig. 18, where a continuous water piping 
 system is connected through appliances to gas services. Although 
 the gas mains are laid with cement joints, they are being damaged 
 by current brought to them over the water mains. 
 
 The application of pipe drainage under conditions here de- 
 scribed may afford protection to some portions of the piping 
 system and increase the damage to others. In some areas gas 
 services and water services are connected with each other through 
 appliances so that at these locations the two piping systems are 
 maintained at practically the same potential. In most piping 
 networks, however, there will be extensive areas where the gas and 
 water systems are not interconnected by such appliances and 
 even where they do exist they cannot always be relied upon to 
 maintain the two systems at practically the same potential. 
 
92 DESIGN, CONSTRUCTION, OPERATION, ETC. 
 
 (c) Effects of Different Kinds of Pipe and Joints. A fundamental 
 difficulty in applying electrical drainage to piping systems is 
 usually present and this is the great variation of conductivity of 
 different kinds of pipes and of different joints. In any cast iron 
 piping system the resistance of the joints varies through wide 
 limits. In many cities there are a number of different kinds of 
 pipes in use: steel mains with welded or screw joints have a low 
 resistance; steel mains with gaskets made of rubber are high in 
 resistance, while cast iron mains with cement joints are unusually 
 high in resistance. With electrical drainage the current on the 
 pipes is increased and the potential drop along these pipes and 
 over the joints is increased in like proportions. 
 
 Because of these conditions it is difficult to apply drainage 
 without increasing the potential differences between the different 
 piping systems at some points. 
 
 SUMMARY OF GOOD PRACTICE 
 
 This summary is intended only as an annotated index or guide 
 to the contents of Chapter 2 of this report, not as a substitute. 
 Before forming an opinion or taking even preliminary action on 
 any subject treated in the report the full text should be studied. 
 
 A. RAILWAYS 
 
 1. Track Construction and Bonding. (See Page 25.) 
 
 (a) The use of heavy rails with joints properly bonded and well 
 maintained is the first requirement for good track conductivity 
 and the minimizing of stray currents. 
 
 (b) In paved streets welded rail joints are regarded as the best 
 and most permanent form of bonding. 
 
 (c) Rail joints including three feet of rail which have a resistance 
 in excess of 10 feet of adjacent rail should be rebonded, except 
 joints bonded with long bonds, which should be renewed when 
 the resistance exceeds that of 15 feet of adjacent rail. 
 
 (d) Bonded joints should be tested at least once each year and 
 such tracks as show bond failures in excess of 5 per cent annually 
 should be tested every six months. A failure is here defined as 
 exceeding the resistance specified in paragraph (c). 
 
 (e) Cross bonds, connecting the two rails on single track, and 
 the four rails on double track should be installed at intervals not 
 to exceed 500 feet in city systems and from 1,000 to 2,000 feet on 
 interurban lines. 
 
DESIGN, CONSTRUCTION, OPERATION, ETC. 93 
 
 (f) Jumpers of one or more conductors should be used around 
 all special work, and should connect to all rails on both sides of 
 the special work. The size of such jumpers should be proportioned 
 to the current on the rails, but in no case should they be smaller 
 than No. 0000 for one track. In addition, where practicable, all 
 special track work should be bonded and maintained as other 
 track rails. 
 
 2. Track Insulation. (See Page 31.) 
 
 (a) In the construction of electric railway tracks and roadbeds 
 the electrolysis problem should be given consideration with 
 economy of construction, maintenance, and operation. 
 
 (b) Roadbeds should be constructed with as high electrical 
 resistance to earth as consistent with other considerations, special 
 attention being given to keeping them dry by drainage. Where 
 practicable, rails should be kept out of contact with the earth. 
 
 (c) Clean crushed stone ballast offers a much greater electrical 
 resistance to stray current than does solid concrete as a foundation 
 under ties. 
 
 (d) Where crushed stone or gravel ballast is used it should be 
 kept clean. If earth, sand, or street dirt is permitted to filter 
 into ballast of this character its insulating property is greatly 
 impaired. Vegetation should be kept down, as this tends to make 
 the roadbed moist and to fill the ballast with foreign material. 
 
 (e) Salts, which are often used to prevent freezing at switches 
 and frogs, greatly reduce the resistance of roadbeds and should 
 be avoided as much as possible. 
 
 (f) Zinc chloride and similar chemical tie preservatives reduce, 
 while creosote and gas oil increase the electrical resistance of ties. 
 
 3. Reinforcement of Rail Conductivity. (See Page 32.) 
 Copper is not economically employed when connected in parallel 
 
 with tracks, and therefore subjected to the same voltage drop as 
 exists on the tracks, as it cannot be loaded to capacity with track 
 voltage drops ordinarily permissible. 
 
 Buried copper conductors or old rails used to supplement the 
 track return also increase the contact area between the return 
 circuit and the earth and thereby tend to augment stray currents. 
 For these reasons the use of such supplementary conductors 
 should be avoided. 
 
94 DESIGN, CONSTRUCTION, OPERATION, ETC. 
 
 4. Power Supply. (See Page 33.) 
 
 (a) Power supply stations for electric railways should be located 
 with consideration to their effect on overall potentials and potential 
 gradients in the tracks. 
 
 (b) In selecting locations for substations, particularly for 
 interurban lines, consideration should be given to the extent and 
 character of the underground* metallic structures in their im- 
 mediate vicinities. 
 
 (c) Connections to tracks in wet locations or the installation of 
 bare track feeders in earth or in water courses should be avoided. 
 
 (d) Numerous independent connections to the track for the 
 return of current aff<prd the most effective means of reducing high 
 potential gradients and overall voltages and thereby limiting 
 stray currents, and as many should be provided as consistent with 
 good engineering and economic considerations. 
 
 This can be accomplished by the use of additional power supply 
 stations, by the installation of insulated negative return feeders, 
 or by the three-wire system wherein each car on the negative 
 trolley becomes a point of return. Combinations of these may 
 also be employed. 
 
 (e) The most generally satisfactory method of increasing the 
 number of independent return points on a track system is by the 
 use of additional substations and the tendency of railway practice 
 is now in this direction. 
 
 (f) Considerable progress has been made in recent years in the 
 development of automatic, semi-automatic, and remote control 
 substations and these are now being used both on interurban lines 
 and for city service. The economies attending such substations 
 make possible a greater number of feeding points than can economi- 
 cally be supplied through manually operated stations. 
 
 (g) By employing the maximum number of substations con- 
 sistent with economy, rather than the minimum number, stray 
 currents will be greatly reduced. 
 
 5. Interconnection of Tracks. (See Page 47.) 
 
 As a rule, interconnection of tracks will improve general elec- 
 trolysis conditions, but may be detrimental in one locality while 
 improving conditions in another. 
 
 6. Insulated Negative Feeder System. (See Page 49.) 
 
 (a) Track gradients and overall potentials can be limited to 
 any desired extent by the use of insulated negative feeders but 
 the cost of such installations, the additional power loss accompany- 
 
DESIGN, CONSTRUCTION, OPERATION, ETC. 95 
 
 ing their use and the reduction in operating voltage at the cars 
 may make their use uneconomical except in connection with 
 frequent power supply stations. 
 
 (b) In general in the application of insulated negative feeders, 
 the negative bus should be connected to the track at more than one 
 point, that is, negative feeders should be extended along the track 
 to nearby intersections. Small stations of 300 to 500 kw. capacity 
 in city networks may usually be connected directly to the track 
 at one point only and preferably to the nearest track intersection. 
 
 (c) Insulated negative feeders should be run from the negative 
 bus to the rails in such a manner as to insulate them thoroughly 
 from the earth and from each other. The tying together of any 
 of these feeders should be avoided. In some cases, however, it 
 may be allowable to tie a single feeder to the rail at two or more 
 points through resistances to adjust the currents drawn from the 
 tracks at the various points of connection. 
 
 (d) Connections to tracks should preferably be made in dry 
 rather than in wet locations. 
 
 (e) Means should be provided on all negative feeders and 
 feeder taps for conveniently measuring the current flow thereon 
 and where practicable these means should be installed within the 
 power supply station. 
 
 (f) Insulated negative feeders are not as well adapted to 
 reducing stray currents from interurban lines as from city networks. 
 
 7. Three-Wire System. (See Page 57.) 
 
 (a) The three-wire method of railway power supply will greatly 
 reduce stray currents when properly applied and also give better 
 operating voltage at the cars. 
 
 (b) Where a few large supply stations are used the first cost of 
 converting an existing railway system for three-wire operation 
 is usually smaller than the first cost of any other measure which 
 will give the same degree of protection from electrolysis. 
 
 (c) There are difficulties to be encountered in connection with 
 three-wire operation which should be carefully considered before 
 adopting that system. 
 
 8. Reversed Polarity Trolley System. (See Page 62.) 
 
 (a) With reversed polarity the amount of stray current is not 
 reduced but the electrolytic corrosion will be scattered over the 
 outlying districts instead of being confined to the vicinity of the 
 power supply station. With reversed polarity the drainage of 
 cable sheaths is rendered impracticable. 
 
96 DESIGN, CONSTRUCTION, OPERATION, ETC. 
 
 (b) This measure should not be considered except as a tem- 
 porary means of relieving dangerous conditions in the vicinity of 
 the power supply station at the expense of the cables and piping 
 systems at a distance from the station, pending the installation 
 of an effective method of electrolysis mitigation. 
 
 9. Periodic Reversal of Trolley Polarity. (See Page 63.) 
 
 (a) If the polarity of the trolley system is reversed daily, 
 electrolytic corrosion will be materially reduced although the 
 drainage of cable sheaths will be rendered complicated or imprac- 
 ticable. 
 
 (b) Some of the difficulties attending three- wire operation 
 will also be encountered with the periodic reversal of the trolley. 
 
 10. Double Contact Conductor Systems. (See Page 65.) 
 
 (a) Practically complete immunity from electrolysis can be 
 had by the use of a properly maintained double contact conductor 
 system either underground or overhead, but the expense and 
 difficulties involved in such an installation are not justified merely 
 as a means of electrolysis protection. 
 
 11. Alternating Current Systems. (See Page 46.) 
 
 (a) Electrolysis resulting from the use pf alternating current 
 by street railways is negligible. 
 
 B. AFFECTED STRUCTURES 
 
 1. Location with Respect to Tracks. (See Page 66.) 
 
 (a) The close approach of piping systems to railway tracks and 
 the laying of shallow service pipes under tracks should be avoided 
 as far as practicable. 
 
 (b) On streets in positive areas where car tracks exist gas and 
 water mains are sometimes installed on both sides of the streets. 
 Such construction permits the use of shorter services and obviates 
 the necessity for placing service pipes under tracks. 
 
 2. Avoidance of Contact of Cables with Pipes and Other Struc- 
 
 tures. (See Page 66.) 
 
 (a) In the installation and maintenance of cable systems 
 precautions should be taken to avoid contact between lead sheaths 
 and other underground structures, such as foreign cables, rails, 
 steel bridges, gas or water pipes and the steel frames of buildings, 
 except as such contacts may be required for specific reasons. 
 
DESIGN, CONSTRUCTION, OPERATION, ETC. 97 
 
 3. Conduit Construction. (See Page 67.) 
 
 (a) Cable sheaths should be kept out of intimate contact 
 with the earth by the use of suitable duct materials, proper conduit 
 construction, and Adequate conduit drainage. Dips in the conduit 
 where moisture might collect should be avoided wherever prac- 
 ticable. 
 
 (b) The use of iron pipe for laterals to poles and buildings 
 should be confined to conditions where no other form of conduit 
 is suitable or permissible. 
 
 (c) Wherever long laterals to poles are installed the horizontal 
 portion should be of vitrified tile, fiber, stone or some similar 
 duct material, using iron pipe only for the bend at the base of 
 the pole and for the vertical portion up the pole. 
 
 (d) Unless necessary as a protective measure for isolated 
 sections, cable sheaths should not be artificially grounded. 
 Grounds in negative areas through which stray current might be 
 picked up should be avoided whenever practicable. 
 
 4. Insulating Joints in Cable Sheaths. (See Page 70.) 
 
 (a) Insulating joints are sometimes used in cable sheaths 
 under special conditions to prevent electrolytic injury which 
 might result from contact with steel bridges or buildings. They 
 are also occasionally used to prevent the flow of current on cable 
 sheaths where drainage is undesirable or impracticable. 
 
 5. Surface Insulation of Pipes and Cables. (See Page 71.) 
 
 (a) Surface insulation in the form of dips, paints, and wrappings 
 cannot be depended upon as a permanent method of preventing 
 electrolysis. 
 
 (b) Thick coatings in the form of pitch or parolite poured 
 into a containing box built around the pipe are occasionally used 
 in preventing electrolysis under special conditions where the 
 expense is warranted. 
 
 6. Insulating Joints in Pipes. (See Page 74.) 
 
 (a) Insulating or high resistance joints, such as those of the 
 Dresser type or cement joints, if used throughout a pipe line at 
 frequent intervals, or at specially selected locations may afford 
 substantial protection against electrolysis. This practice relates 
 particularly to gas and oil pipes. 
 
 (b) It is sometimes permissible to use a comparatively few 
 insulating joints if care is taken to see that the flow of current 
 on the pipe is practically eliminated. 
 
98 DESIGN, CONSTRUCTION, OPERATION, ETC. 
 
 (c) Insulating joints are often installed in service pipes for the 
 purpose of preventing the interchange of current between pipe 
 systems. 
 
 7. Shielding. (See Page 79.) * 
 
 In special locations a pipe may be protected from electrolysis 
 by a metal shield, wholly or partly surrounding it and electrically 
 connected thereto. 
 
 C. INTERCONNECTION OF AFFECTED STRUCTURES AND 
 RAILWAY RETURN CIRCUIT 
 
 1. Cable Drainage. (See Pages 81 and 83.) 
 
 (a) Lead sheath cables in urban districts or where parallel 
 with interurban railways commonly require some form of elec- 
 trolysis protection and this is usually accomplished by drainage. 
 
 (b) In some cases the heating effect of stray current on the 
 sheaths of power cables may reduce the current carrying capacity 
 of the cable. 
 
 (c) Drainage connections should be made to the negative bus 
 of the railway supply station or to the rail terminal of insulated 
 negative feeders. Connections to the rails should in general be 
 avoided. 
 
 (d) Cable sheaths when drained are made negative to the 
 surrounding earth at practically all times. Drainage should be 
 reduced to a minimum consistent with the protection of the 
 cables. 
 
 (e) In general, all signal cable sheaths in any conduit system 
 should be bonded together at every man hole. Where advisable 
 and permissible all power cable sheaths should be similarly 
 bonded. 
 
 (f) So far as practicable or advisable, all cable systems should 
 be drained at the same locations or by the same drainage feeders 
 and differences of potential between adjacent or intersecting cable 
 systems should be eliminated by cross bonding. 
 
 (g) Fuses should be installed in all connections between signal 
 and power cable sheaths, and should be so proportioned as to 
 protect the sheaths from dangerous currents. 
 
 (h) Means should be provided for conveniently measuring all 
 drainage currents and maintaining close supervision on all drainage 
 systems, and where possible this should be accomplished by in- 
 stalling meters within the power supply station and making them 
 accessible to the cable owning companies. 
 
DESIGN, CONSTRUCTION, OPERATION, ETC. 99 
 
 (i) Means and operating regulations should be provided for 
 opening all drainage cables during periods when reverse currents 
 would otherwise flow over them, if the magnitude and duration 
 of such reverse currents is objectionable. 
 
 2. Pipe Drainage. (See Pages 88 to 91.) 
 
 (a) There are wide differences of opinion among competent 
 engineers who have studied pipe drainage, as to its adaptability 
 to various conditions. Numerous questions are involved in 
 regard to which there is not sufficient information available at 
 the present time to permit the drawing of accurate conclusions, 
 and for this reason this subject is being investigated by the 
 Research Sub-Committee of the American Committee on Elec- 
 trolysis. There are, however, certain objections to the use of 
 pipe drainage which are discussed in this report and which should 
 be carefully considered before employing it. 
 
 (b) Pipe drainage is in use more or less on water systems and 
 to a limited extent on gas systems. 
 
 (c) As a method of mitigation, drainage is not so well adapted 
 to pipes as to cable sheaths. 
 
 (d) High resistance joints are prevalent in all jointed pipe lines 
 and they greatly complicate the application of drainage. 
 
 (e) To lower the potential of a jointed piping system below 
 that of the surrounding earth, it is usually necessary to extend 
 the drainage conductors over a considerable area and connect 
 to the pipes at numerous locations. 
 
 (f) Corrosion at high resistance joints in pipe lines carrying 
 current may occur unless the pipe on both sides of the joint is 
 maintained negative or neutral to the adjacent earth, in which 
 case no corrosion will occur. 
 
 (g) Drainage generally increases the current flow on pipes 
 and such current increases the hazard from oil and gas ignitions 
 and explosions. 
 
 (h) In small towns on interurban railways pipe drainage is 
 less objectionable than in urban districts where complicated pipe 
 networks exist. 
 
 (i) Drainage of a large network of pipes should be used only 
 as an auxiliary to a railway system, properly designed and main- 
 tained from the electrolysis standpoint. When so used it should 
 be installed and maintained under competent supervision. 
 
CHAPTER 3 
 ELECTROLYSIS SURVEYS 
 
 I. INTRODUCTION 
 A. PURPOSE AND SCOPE OF ELECTROLYSIS SURVEYS 
 
 1. Purpose of Electrolysis Survey.* 
 
 Electrolysis surveys deal with the various methods and classes 
 of measurement employed to determine the hazard to underground 
 metallic structures due to stray electric currents, the extent of 
 existing damage already produced, and the mitigative measures 
 that may best be employed for reducing the danger of future 
 trouble. There are discussed below the methods of determining 
 electrolysis conditions, of collecting data upon which the design 
 of mitigating systems may be based, the types and kinds of 
 instruments that should be used, the procedure to be followed in 
 the working up of the data, and the interpretation of the results 
 of the survey. 
 
 2. Difficulty of Standardizing Survey Procedure. 
 
 It should be emphasized that in general, no two electrolysis 
 surveys will be conducted in precisely the same manner, so that 
 specific rules of procedure cannot be laid down that will be appli- 
 cable to all cases. The procedure set forth below is intended to 
 cover the measurements that experience has shown are most 
 frequently required, and to describe the best methods of taking 
 such measurements. The number of readings taken and the 
 procedure to be followed will vary so much with local conditions 
 that reliance must be placed on the judgment of the person making 
 the test. In fact, the proper procedure during a large part of the 
 survey will depend in large measure on the results obtained in 
 preliminary tests. It is important, therefore, that electrolysis 
 investigations of any importance be made under the direction of 
 a competent engineer very familiar with methods of procedure 
 and the interpretation of electrolysis test data. 
 
 3. Information Obtainable by Electrolysis Surveys. 
 
 By means of proper measurements, it is possible to determine 
 
 with a fair degree of defmiteness, the extent and location of the 
 
 % 
 
 *For a definition of the term electrolysis survey and other terms used in this 
 chapter, see Chapter 1, on Principles and Definitions. 
 100 
 
ELECTROLYSIS" $AVS'< -' 101 
 
 areas in which pipes and other structures are endangered by 
 stray currents and, with sufficient accuracy for most purposes, 
 the degree of seriousness of the trouble. The cause of any damage 
 that may be in progress at the time of the survey, whether due to 
 stray currents or corrosion by the soil, cinders, or other natural 
 causes, can generally be ascertained, and in the case of stray 
 current corrosion, the source of the current can generally be deter- 
 mined. The various factors connected with pipe systems, such 
 as high resistance joints, very low soil resistances, and the use of 
 improper mitigative measures, can also be detected. Defects 
 in the railway return system, such as poorly bonded rail joints, 
 infrequent cross bonds, insufficient conductance in the negative 
 return, improper use of such conductance, excessive feeding 
 distances and other causes of electrolysis trouble can usually be 
 
 definitely determined. 
 
 
 
 B. TYPES OF SURVEYS 
 
 In the following discussion several types of surveys must be 
 recognized. The first is that which may be called a complete 
 electrolysis survey which is made for the purpose of determining 
 the extent and location of the danger areas, and with a view of 
 determining the proper procedure to be followed for the mitiga- 
 tion of any trouble which may be found to exist 
 
 The second type of survey, known as a maintenance survey, 
 embraces such surveys as would usually be made by a pipe or 
 cable owning company, solely for the purpose of determining 
 whether previously existing conditions have changed and differs 
 from the more complete survey mainly in that most of the in- 
 formation with respect to the railway power distribution system 
 is not required and fewer electrical measurements are taken, the 
 number and character of such measurements depending on the 
 thoroughness with which the survey is to be carried out. 
 
 A third type of survey which needs little discussion, except as 
 to methods of making tests, is one made to determine whether 
 ordinances or regulations governing electrolysis conditions in a 
 municipality are being complied with. Such surveys are usually 
 made periodically, in periods varying from three months to a year. 
 In general, only those quantities are measured which are speci- 
 fically defined by the ordinances or regulations which are in 
 effect in the locality in question. 
 
102 riMCTROLYSIS SURVEYS 
 
 C. GENERAL PRELIMINARY DATA 
 
 1. Data on Underground Structures. 
 
 In making electrolysis surveys, a considerable amount of 
 preliminary data are usually desirable. It is important first to 
 gather all evidence regarding the character, extent and location 
 of known damage to underground structures. This evidence is 
 usually obtained from the utility companies concerned, but even 
 though these companies can give no direct testimony as to the 
 injury to underground structures, this should not be taken to 
 indicate that no damage exists. The data on the underground 
 systems should include the relative location of the mains, the rail- 
 way tracks and underground cable systems. The size and kinds 
 of pipe and the types of pipe joints used are usually important. 
 Numerous questions relating to the interconnection of gas, water, 
 and cable systems are also of importance. 
 
 2. Data on Railway Systems. 
 
 As regards the data on the railway systems, the following 
 should be determined: (1) Location and capacities of direct 
 current railway supply stations : (2) Location of railway lines and 
 character of service, whether city, suburban, or interurban and 
 the car schedules on different parts of the system. This latter 
 will have a bearing on the length of time necessary for taking 
 readings at various points in order to get representative results; 
 (3) Physical data on railway tracks, such as size of rails, types of 
 bonds and joints, and character of roadbed construction; (4) 
 Practice of the railway company in regard to crossbonding, 
 bond maintenance and bond testing; and (5) Miscellaneous data. 
 In most cases it is desirable to have all-day load curves to facilitate 
 the interpretation of data taken over short intervals at various 
 hours of the day. Where the load varies considerably in different 
 sections of a power house feeding area, it may be necessary to 
 get the load curve on different feeders in some cases. Where a 
 survey is made with the ultimate purpose of correcting electrolysis 
 conditions by applying some method of mitigation, it will be 
 necessary to secure complete data on the magnitude and distribu- 
 tion of the load, the substation and feeder systems, frequency of 
 schedules and probable future growth of traffic. 
 
 D. COOPERATION IN MAKING SURVEYS 
 
 Special surveys for determining whether ordinances are being 
 complied with and maintenance surveys can usually be made 
 by any particular utility interested. Complete surveys, however, 
 
ELECTROLYSIS SURVEYS 103 
 
 which are to be preliminary to the application of electrolysis 
 mitigative measures should preferably be carried out on a coopera- 
 tive basis by the various utilities interested, including both the 
 railways and owners of underground utilities. It is of the utmost 
 importance that a comprehensive plan of procedure be followed, 
 so that all information relating to the electrolysis conditions of 
 all of the underground structures may be available in the planning 
 and carrying out of the test. In order to bring about such a 
 unification of data and methods, it is necessary to have the full 
 cooperation of all utilities whose properties are affected by elec- 
 trolytic conditions. In general, this cooperation can best be 
 brought about by having the electrolysis survey and the mitiga- 
 tive measures, if any are to be applied, designed and installed 
 under the jurisdiction of a joint committee representing all of the 
 interests concerned or at the discretion of such committee by an 
 engineer employed by the committee, or jointly by the parties to 
 the survey. 
 
 II. ELECTRICAL MEASUREMENTS 
 
 The electrical measurements to be made during an electrolysis 
 survey may be logically classified in either of two ways, namely, 
 (1) on the basis of the structures on which the measurements are 
 to be made, that is, whether on the railway system, pipe system, 
 or cable system, and (2) on the basis of the character of the 
 measurements, whether of voltage, current on, or current leaving 
 a structure, etc. Inasmuch as several or all of the various types 
 of electrical measurements may at times have to be made on all 
 of the affected structures, and since the methods used will be sub- 
 stantially the same regardless of the utility system to which they 
 apply, it appears most logical to follow the latter classification 
 and discuss the subject from the standpoint of the character of the 
 measurements to be made. 
 
 A. VOLTAGE SURVEYS 
 
 The number and character of the potential readings required 
 depend on the information desired. As previously pointed 
 out, the readings depend on the thoroughness of the investigation 
 to be made, and it is to be understood that many of the measure- 
 ments described below would often not be necessary, and in 
 general would be taken only during the course of a complete 
 electrolysis survey. Voltage surveys are here divided into two 
 main classes: (a) Voltage measurements between two points on 
 
104 ELECTROLYSIS SURVEYS 
 
 the same structure, and (b) Measurement of the potential differ- 
 ence between structures. 
 
 1. Measurement of Maximum Potential Drop Along Railway 
 Structures. 
 
 (a) Importance of Maximum Potential Drop Measurements. 
 Such measurements, when interpreted in the light of other con- 
 ditions to be discussed later, afford a valuable index to electrolysis 
 conditions generally. It is, further, one of the easiest quantities 
 to determine in an electrolysis survey if the use of telephone lines 
 can be secured. These measurements show in general whether 
 the railway system is properly 'maintained and what lines or sec- 
 tions are most in need of repair and rebonding. When taken in 
 conjunction with the load data, they may be used for an approxi- 
 mate calculation of power losses in the railway return and when 
 studied with due regard to the character and location of railway 
 lines and supply stations, together with the distribution of load, 
 they afford a valuable index as to the need of, or the modification 
 of the track feeder system. It is therefore desirable, as a rule, 
 to take a good many of these measurements as a part of any 
 complete electrolysis survey. 
 
 (b) Procedure in Making Maximum Potential Drop Measure- 
 ments. The first step in making measurements of this kind 
 in a city is to determine the location of points between which 
 potentials are to be observed. These usually comprise points on 
 the track most remote from the power supply station as the 
 points of highest potential, and the points on the track nearest 
 the power station as the point of lowest potential. In some cases, 
 however, especially where insulated track feeders are used, the 
 point of lowest potential may be at the point of connection of 
 one of the insulated feeders which may be at a considerable 
 distance from the power station. It is desirable, as a rule, to 
 measure the difference of potential between the points of connec- 
 tion to the tracks of all of the insulated track feeders in order 
 that the points of lowest potential may be determined. It is 
 desirable, as a rule, also to select points intermediate between the 
 points of highest and lowest potential so that the distribution of 
 the potential drop may be determined, as this will give a valuable 
 insight into the location of bad stretches of track and of concen- 
 tration of return current in the tracks. 
 
 Reference should be made to a positive feeder map from which 
 a list of power stations and their approximate feeding distances 
 can be determined. Special lines to these points may be run or 
 
ELECTROLYSIS SURVEYS 105 
 
 spare wires may be borrowed or leased from the telephone company. 
 In the latter case, the continuous cooperation of the telephone 
 company is required. Having a list of points to be reached, the 
 telephone representatives can prepare a table showing the ter- 
 minal boxes and numbers of spare pairs, including trunk lines 
 which are necessary to make a complete circuit between one of the 
 telephone central offices, or other suitable central point where 
 the measuring instruments are to be placed and the points to which 
 measurements are to be made. All measurements can then be 
 made between the point of lowest potential and all other points 
 selected, and between any two points as desired. Temporary 
 circuits are necessary when no spare telephone conductors are 
 available, in which case working conductors may sometimes be 
 used for short periods. In most cases, it is desirable to make 
 permanent connections to the track for maximum voltage drop 
 measurements, but where for any reason, permanent or semi- 
 permanent connections to the track cannot be made, temporary 
 connections become necessary and the installation of these tem- 
 porary connections will require considerable time and expense 
 for labor. 
 
 It will be found most convenient to bring all the lines from the 
 various points on the track network to a large board on which is 
 mounted a map of the railway system, each wire being fastened 
 to a binding post located at a point on the map corresponding to 
 the point on the track from which the wire comes. Once the 
 correct connection of wires has been verified, one can readily 
 connect the voltmeter to wires leading to any points in the city 
 without possibility of error. 
 
 While making track voltage measurements, and in fact, all 
 other measurements, it is desirable to arrange to have the test 
 data worked up and tabulated so that it can be carefully studied 
 as the work progresses. This is important because, as pointed 
 out above, the tests to be made during the course of the survey 
 often depend in large measure on the results of preliminary 
 measurements so that by .making a study of the preliminary data 
 while the work is in progress, it is often possible to modify original 
 plans in such a way as to greatly increase the value of the test 
 data. 
 
 In making electrolysis measurements, it is desirable to take 
 readings at each point over as long a period as practicable. Owing 
 to the great variability of railway loads, it is important to have 
 the readings cover at least one complete cycle of the load, and 
 
106 ELECTROLYSIS SURVEYS 
 
 often several complete cycles are desirable. It is quite common 
 practice to take such readings over a period of one hour, but in 
 some cases, especially on interurban lines and others where the 
 schedule is very infrequent, still longer periods may be necessary. 
 Even where readings are taken over one hour it will generally 
 be necessary for comparative purposes to reduce these readings 
 to an equivalent twenty-four-hour value, and in some cases also 
 corrections have to be made for seasonal changes of the load. 
 This matter will be treated at some length under the discussion 
 of the interpretation of electrolysis survey data. 
 
 2. Potential Gradient Measurements. 
 
 (a) Scope of Term. Under the head of potential gradients 
 will be included all potential measurements between different 
 points on the track or between different points in the earth spaced 
 materially less than the extreme feeding distances within the 
 powerhouse areas. 
 
 (b) Measurement of Potential Gradients in Tracks. Potential 
 gradient measurements are usually made on the railway tracks, 
 but at times also on pipe systems or even in the earth. The 
 procedure will vary considerably because of the variability of the 
 distances over which measurements are to be made. If the 
 spans are long, telephone wires are the most convenient and the 
 measurements are made in the same way as track voltage measure- 
 ments described above. Where the distances are relatively 
 short, however, as for example, a few hundred feet or less, a 
 temporary wire between the two points of measurement will 
 usually be most convenient. Connections to the system on which 
 measurements are made will depend on whether the tests are being 
 made between points on the tracks or on the pipe system or 
 between points in the earth. For measurements between points 
 on the tracks or on the pipe system or other metallic structure 
 metallic terminals may be firmly held against the rail or pipe 
 or a wire may be swedged in a slot sawed in the pipe or rail under 
 test. It is sometimes desirable to make potential measurements 
 directly between two points in the earth, though the most common 
 practice has been to take them on the track network. Special 
 situations may arise where potential measurements between 
 various points in the earth are more valuable than those taken 
 on the underground structures. For example, the presence and 
 direction of large transverse currents in the vicinity of important 
 mains can be determined. Buried pipe lines or other conductors 
 
ELECTROLYSIS SURVEYS 107 
 
 at uncertain locations which are discharging current into the 
 earth may be located approximately by earth gradient measure- 
 ments, there being a reversal or abrupt change in the gradient 
 when the conductor is crossed. 
 
 In making earth gradient measurements between points rel- 
 atively close together, it is essential that a pair of non-polarizable 
 electrodes be used if a high degree of accuracy is to be attained. 
 Such electrodes are now in process of development at the Bureau 
 of Standards. 
 
 The periods over which gradient measurements should be made 
 and the procedure in working up the data during the progress 
 of the survey are governed by the same considerations as dis- 
 cussed above in the treatment of the track voltage measurements. 
 
 3. Measurement of Potential Differences. 
 
 (a) Purpose of Measurement of Potential Differences. Measure- 
 ment of potential differences are beyond question the measure- 
 ments most frequently made in connection with electrolysis 
 tests and when their limitations are properly taken into account, 
 they afford a valuable index to electrolysis conditions. It should 
 be emphasized, however, that they are chiefly of qualitative sig- 
 nificance, being valuable for indicating the region in which more 
 or less damage to pipes may be in progress, but not giving any 
 definite information as to the rate at which injury to pipes may 
 be progressing. This is due to the fact that the resistivity of the 
 earth and railway roadbed varies with local conditions, that is, 
 a given potential difference that would be practically safe under 
 some conditions of soil resistance would be extremely hazardous 
 in other locations. If this factor is properly taken into account, 
 potential difference measurements may be of considerable value 
 in determining electrolysis conditions. 
 
 (b) Procedure in Making Measurements of Potential Differences. 
 Measurements of potential differences between adjacent structures 
 should be made at many points between fire hydrants, lamp posts 
 or gas or water services and tracks, lead cable sheaths and tracks, 
 lead cables and accessible portions of pipe systems, between any 
 two pipe systems that approach closely to each other, and where 
 practicable between cable systems and the earth. In making 
 contacts on fire hydrants and lamp posts, care should be taken to 
 make contact with the pipe itself, rather than the housing. These 
 measurements, between cable systems and earth, if properly 
 taken, afford the most valuable index of electrolysis conditions, 
 but unfortunately, they are the most difficult to secure, and 
 
108 ELECTROLYSIS SURVEYS 
 
 unless taken by a competent engineer, thoroughly familiar with 
 the possible sources of error involved, they may be worthless or 
 actually misleading. These measurements when taken should 
 be made throughout a large part of the piping or cable networks 
 including any regions in which there is reason to believe that 
 stray current may be leaving the affected structures for the 
 earth. 
 
 Since the structures between which potential difference measure- 
 ments are made are usually close together, short leads only are 
 required, short lengths of lamp cord or other flexible wire being 
 most commonly used. Either temporary or more or less per- 
 manent connections to metallic structures may be made, accord- 
 ing to whether readings are to be taken over a short or long period 
 and whether they are to be repeated at some future time. When 
 measuring potential differences between pipe or cable systems 
 and the earth, it is important to use an auxiliary earth electrode 
 that is known to give a very small galvanic potential against the 
 metal of the structure under test. For lead cables a piece of 
 ead sheath is entirely satisfactory. In the case of iron pipes thel 
 problem is more difficult because of the variability of iron and 
 the possibility of complication due to oxidation of either the pipe 
 under test or the auxiliary iron electrode. When such readings 
 with iron electrodes amount to only a few tenths of a volt they 
 should not be regarded as reliable unless taken over a period in- 
 cluding that during which the railway power station is shut down, 
 owing to the possibility of galvanic voltages being of this order 
 of magnitude. 
 
 B. CURRENT SURVEYS 
 
 1. Scope and Importance of Current Measurements. 
 
 Under the head of current measurements are included all ob- 
 servations of current flow obtained by ammeter readings, or by a 
 potential drop on a conductor, the resistance of which is approxi- 
 mately known. They include measurements of current flowing 
 from subsurface structures into the earth. 
 
 Current measurements on undrained structures made both before 
 and after a change in the railway system or the application of other 
 mitigative measures afford considerable information as to the 
 change in electrolysis conditions. Owing to the great variety of 
 conditions under which it is at times necessary to measure cur- 
 rent, as in copper feeders, rails, pipes, cable sheaths, and even 
 
ELECTROLYSIS SURVEYS 109 
 
 in portions of the soil, the methods of procedure may vary con- 
 siderably. 
 
 2. Measurement of Currents in Feeders and Rails. 
 
 (a) Purpose of Measuring Feeder and Rail Currents. Measure- 
 ments of current in track feeders and rails are usually made only 
 when it is desired to check the current distribution in a network 
 of tracks. Current measurements on the track will show the 
 points at which additional track feeders are required in order to 
 limit potential gradients in the track as well as the amount of 
 current that must be taken off at each point, and consequently 
 the sizes of feeders required. The same result can be obtained with 
 sufficient accuracy for most practical purposes by the use of a 
 "spot map" on which are shown the average distribution of cars 
 and their corresponding loads. Further, by measuring current in 
 different rails in the track, local bad bonding will be revealed 
 since unequal distribution of current always indicates relatively 
 high resistance in the rails carrying the lower currents. In fact, 
 some engineers regard the measurement of the relative current 
 in the rails at a number of points as the most reliable way of 
 obtaining in a short time a good idea of the condition of track 
 bonding. 
 
 (b) Procedure in Measuring Current in Feeders and Rails. 
 The most accurate method of measuring current in a feeder of 
 rail is of course, afforded by inserting an ammeter shunt directly 
 in series with the feeder or rail under test. However, in practice 
 it often happens that in the case of negative feeders ammeters or 
 shunts are not provided and can be inserted only with difficulty, 
 and in the case of rails this is impracticable. The most common 
 method, therefore, of measuring current in such structures is to 
 measure the potential drop on a known length of cable or rail 
 and to calculate the current from this potential drop and the 
 resistance of the conductor. Such measurements of current 
 can be made on copper cables with high accuracy and on steel 
 rails the results can usually be relied upon to 10 per cent or better, 
 which is sufficient for practically all purposes. In making the 
 current calculations it is customary to consider the resistivity of 
 the copper at 10.7 ohms per circular mil-foot, and that of steel 
 rails to be 0.0003 ohm per pound-foot, this latter being equivalent 
 to a resistance of 0.000009 ohm for one foot of rail weighing 
 100 pounds per yard. In practice it may be expected, however, 
 that the resistance per pound-foot may vary between the values 
 
110 ELECTROLYSIS SURVEYS 
 
 of 0.00027 and 0.00033, or about ten per cent each way from the 
 mean values here given. Table 5 in the appendix will be found 
 convenient for calculating the current in rails of various weights. 
 
 3. Measurement of Currents in Pipes and Cable Sheaths. 
 
 (a) Purpose and Importance of Pipe Current Measurements. 
 The measurement of current in pipes and lead cable sheaths is 
 important for a number of reasons. Heavy currents in pipes are 
 often objected to by owners of pipe networks, particularly gas 
 and oil pipes owing to the fear that trouble may result from 
 ignition of gas or oil due to arcing when two portions of the 
 pipe network are separated, and also due to arcing between adja- 
 cent pipes in confined air spaces such as cellars where there may 
 be considerable potential differences due to such currents. In 
 some cases also, excessive heating has resulted due to the presence 
 of abnormally large currents on small pipes, and the presence of 
 such heavy currents may make it very difficult to prevent local 
 interchange of current between neighboring structures. Heavy 
 currents on lead power cables are also objectionable because the 
 heat generated in the lead sheath may limit considerably the 
 carrying capacity of the conductors within the sheath. In view 
 of these factors, it becomes important to measure currents on 
 pipes and cables in many instances. Relative current measure- 
 ments on pipe and cable systems made before and after the 
 application of mitigative measures are also valuable as an index 
 of the effectiveness of the mitigative system employed. This is 
 true, however, only when there has been no installation of new 
 drainage connections or change in existing drainage connections 
 on the affected structures. 
 
 (b) Selection of Points of Measurement. In general in selecting 
 points for making current measurements, it is desirable to secure 
 some points at which maximum current flow may be anticipated, 
 and also 'a considerable number of points that may be regarded 
 as representative of conditions generally. As a rule, the maximum 
 current in an undrained pipe network may be expected in pipes 
 extending approximately parallel to the tracks and near the 
 neutral or slightly positive areas. Also numerous cases will 
 usually be found in any network in which one or at most, a few 
 mains serve as connecting links between local networks, and such 
 mains usually will be found to carry much larger currents than 
 mains forming a portion of the network. On drained pipe systems, 
 the maximum currents will as a rule be found in the pipes extend- 
 
ELECTROLYSIS SURVEYS 111 
 
 ing in all directions from the points at which drainage cables are 
 connected. It is impossible to lay down rules more detailed than 
 the above for the selection of points at which measurements 
 should be made. Experienced judgment should be followed in 
 all cases. 
 
 (c) Methods of Measuring Current Flow in Pipes. Four general 
 classes of methods of measuring current flow in pipes and other 
 metallic structures have been used. The one that is perhaps the 
 most frequently used is the ordinary drop-in-potential method in 
 which the voltage drop on a measured length of pipe, not in- 
 cluding a joint, is taken and the current calculated from this 
 voltage drop and the estimated resistance of the portion of the 
 pipe across which the potential drop is measured. Complete 
 tables for the resistance per unit length of the various sizes and 
 kinds of pipe in common use are given in the appendix. Careful 
 tests made on a great variety of specimens of pipe of different 
 kinds, indicate that measurements of this kind can be depended 
 upon to give results accurate to within about 10 per cent, which 
 is ample in most cases encountered in practice. 
 
 A second method, used in special cases where greater accuracy 
 than is possible by the drop-in-potential method is necessary, is 
 the method for calibrating the pipe either by sending a known 
 current through it superposed on the railway current already 
 flowing in the pipe, or by shunting through an ammeter, certain 
 portions of the current actually flowing in the pipe. These 
 methods have taken various forms, one of the most important of 
 which is described later. 
 
 A third method consists in the use of what is known as a direct 
 current ratio relay in a manner somewhat analogous to the use of 
 a current transformer on alternating current circuits. This is 
 useful only where currents of fifty amperes or more flow on the 
 pipe. 
 
 A fourth method consists in surrounding the pipe with an iron 
 ring containing an airgap and providing means for measuring the 
 magnetic flux set up across the airgap by the current in the pipe. 
 Several different methods are available for making these measure- 
 ments. The last two methods may also be used for calibrating the 
 pipes, thus eliminating in some measure the uncertainty arising 
 from the calculation of the pipe resistance. It is questionable, 
 however, whether in most cases the greater accuracy thus achieved 
 is sufficient to warrant the use of the more complicated methods. 
 
112 
 
 ELECTROLYSIS SURVEYS 
 
 J 
 
 s 
 
 -h 
 
 E 
 
 I 
 
 n 
 
 TJ 
 
 <D 
 
 (T 
 c 
 
 15 
 
 (0 
 
 c 
 
 TJ 
 
 o 
 
ELECTROLYSIS SURVEYS 113 
 
 There are given below somewhat detailed descriptions of the first 
 two of these methods. 
 
 Drop-in-Potential Method. This method consists in connecting 
 potential terminals to a section of pipe a few feet apart and meas- 
 uring the millivolt drop, and in calculating the current from this 
 millivolt drop and the resistance of the section under test. It is 
 very widely used, and its great simplicity adapts it to work of this 
 kind. This method has the great advantage that it can not only 
 be used with an indicating instrument but also with a recording 
 instrument unless the currents are very small, and thus not only 
 a permanent graphic record be obtained, but also the average value 
 for a given period can be determined. The tables appended to 
 this report are based on careful measurements made by the Bureau 
 of Standards on several hundred specimens of iron and lead pipes 
 from various sources, and they are accurate enough for all prac- 
 tical purposes. 
 
 In using this method it is necessary to make an excavation at 
 the point where the measurement is to be taken and attach two 
 leads to the pipe, preferably as far apart as practicable without 
 including a joint. This connection may be made in numerous 
 ways, but perhaps the best way is to insert at each point a corpora- 
 tion cock in which a rubber covered wire has been soldered. If 
 the connections are to be permanent, the leads should be brought 
 underground to a point inside the curb and there terminated in an 
 ordinary service box or other suitable receptacle so that they will 
 be protected from traffic but readily accessible for repeating the 
 measurement at any time. One method of making such connec- 
 tions and protecting the leads is shown in Fig. 21, and another 
 which has been very successfully used in paved streets is shown 
 in Fig. 22. It is also important that the junction between wire 
 and corporation cock be protected by painting with a heavy as- 
 phalt or similar paint. If the current on the pipe is large enough 
 to be of practical significance it can be read with an ordinary 
 sensitive millivoltmeter either indicating or' recording. In special 
 cases where the current is extremely small, only a high sensitivity 
 indicating millivoltmeter or even a portable galvanometer can be 
 used. 
 
 Calibration of Pipes. One of the methods most commonly 
 used for the calibration of pipes involves superposing a current on 
 that already in the pipe and measuring the change in millivolt 
 drop due to this superposed current. This method, originally 
 used by Professor B. F. Thomas was first described by Dr. Carl 
 
114 
 
 ELECTROLYSIS SURVEYS 
 
 
ELECTROLYSIS SURVEYS 115 
 
 Hering in the Transactions of the American Institute of Electrical 
 Engineers for June, 1912. Theoretically, this method should 
 give very high accuracy, but it should be borne in mind that the 
 resistance of the pipe thus determined is correct only for the 
 conditions under which the measurement was made. Iron pipes, 
 especially wrought iron and steel pipes, have a high temperature 
 coefficient of resistance and variations in this resistance due to 
 temperature changes between winter and summer may introduce 
 variations of .five per cent or more in this resistance. For this 
 reason, it is very doubtful whether the complication involved in 
 the use of this method is justified, but it has been used by some 
 engineers. Further, owing to the presence of rapidly fluctuating 
 railway currents on the pipes, the application of this method is 
 often difficult. 
 
 Use of a Direct-Current Ratio Relay. An instrument known as 
 the direct-current ratio relay for measuring current in conductors 
 which cannot be opened for the insertion of ammeters or shunts 
 has recently been devised. The ratio relay permits the measure- 
 ment of variable unidirectional currents of relatively large magni- 
 tude only, on an ordinary direct current ammeter. This instru- 
 ment gives very good results when very large currents are being 
 measured, but in its present form it is not suitable for measuring 
 currents of a few amperes, such as are most frequently encountered 
 in electrolysis testing. 
 
 4. Comparing Currents Under Different Conditions. 
 
 In case the object in view is the determination of relative cur- 
 rent in pipes under different systems of mitigation, this can be 
 done simply by measuring potential drops between services or 
 between adjacent fire hydrants. In general, the resistance may 
 be regarded as sufficiently constant so that the currents under the 
 two conditions of test will be proportional to the voltages at 
 corresponding test stations. 
 
 5. Measurement of Current Flowing from Underground Struc- 
 tures to Earth. 
 
 It is extremely desirable to measure the amount of current 
 flowing from a particular portion of a pipe or cable network 
 directly into the earth. In fact, if such measurements could be 
 made conveniently and with sufficient accuracy they would be by 
 far the most important and valuable measurements that could be 
 made in an electrolysis survey, since this measurement would 
 afford the most accurate measure of the rate at which damage is 
 
116 ELECTROLYSIS SURVEYS 
 
 progressing. Unfortunately, there has not been available up to 
 the present time, any very satisfactory method of measuring such 
 current flow except in very special cases. Four different methods 
 have been proposed under special conditions for making this 
 measurement. These are: (a) differential current measurements; 
 (b) the use of a Haber earth current collector; (c) the measurement 
 of polarization potentials; and (d) the combined measurement of 
 potential drop and earth resistivity. The first of these is dis- 
 cussed below. The second and third have been found impractical 
 and the last is still under development. 
 
 (a) Differential Current Measurement. This method of measur- 
 ing current flow from a pipe to earth can be used to advantage 
 where it is desired to measure a current discharge that is com- 
 parable in magnitude with the total current on the pipe. If the 
 measurement is made at two points on the pipe by the potential 
 drop method, uncertainties- in the measured values may be too 
 great to permit an accurate determination of discharge, but if the 
 pipes are carefully calibrated at the points at which the potential 
 drops are measured, fairly accurate results can be obtained, 
 provided the difference in current is as mtlch as ten or fifteen per 
 cent of the total current flowing in the section of the pipe under 
 test. In making current discharge measurements by this method, 
 it is necessary to make sure that there are no service pipes or 
 drainage feeders connected with the portion of the pipe between 
 test points through which current may flow. 
 
 C. MISCELLANEOUS TESTS 
 1. Track Testing. 
 
 Electrical tests are made on railway tracks chiefly for three 
 purposes first, to locate the cause of bad electrolysis conditions 
 that may have been encountered second, to serve as a guide for 
 the systematic maintenance of the railway track network, and 
 third to be used as a guide in designing an electrolysis mitigation 
 system. Three methods of determining the condition of the track 
 system have been extensively used, as follows : 
 
 (a) Inspection. This method of testing bonds by a simple 
 inspection is one which has been used much more extensively in 
 the past than at the present time, but it is unfortunately still 
 very frequently used in open track work. It consists chiefly in 
 going along the track and making superficial inspection of the 
 bonds and if they appear mechanically good, the assumption is 
 made that the bond is in a satisfactory condition. It cannot be 
 
ELECTROLYSIS SURVEYS 117 
 
 too strongly emphasized that any examination of bonds by this 
 simple method of inspection should be regarded as a poor make- 
 shift, and some more reliable method should always be used. 
 
 (b) Use of Portable Bond Tester. There are in use at the 
 present time a number of portable bond testers operating on the 
 principle of a slide wire bridge, a portable milli voltmeter being 
 used to determine when the bridge is balanced. In the use of 
 this instrument the voltage drop across the joint is compared 
 directly by the bridge method with the voltage drop on a definite 
 length of rail directly adjacent to the joint under test, so that the 
 resistance of the joint is measured in terms of an equivalent length 
 of rail. This method has the advantage of simplicity as it can be 
 operated by one man, and while somewhat slow and tedious.it 
 often affords a very satisfactory method of testing bonds. 
 
 (c) Autographic Method of Bond Testing. A method that has 
 been used extensively in recent years for testing the bonds in 
 railway tracks is what is known as the autographic method. This 
 method is like that of the portable bond tester in that it is based 
 on a comparison of the potential drop across a certain length of 
 rail, including the joint, with that across an equal length of 
 adjacent solid rail. The two readings are taken and automatically 
 recorded within a fraction of a second, and during this short time, 
 the current in the rail may be regarded as practically constant. 
 The method, however, permits of a correction in case the current 
 should vary appreciably between two readings. The autographic 
 method has several advantages, chief of which are as follows: 
 
 (1) A special test current is employed so that one does not have 
 to depend on the railway load which is uncertain and at times 
 discontinuous. 
 
 (2) It eliminates the personal element to a large extent, all 
 readings being autographic. 
 
 (3) It gives a permanent record which can be kept on file for 
 future reference. 
 
 (4) A large amount of track can be covered in a short time so 
 that the test of an entire railway system can quickly be made at 
 any particular period. 
 
 The apparatus for this method of testing is quite expensive as 
 a special car is required and sometimes another car is used to haul 
 the test car. Owing to the much greater rate at which bonds can 
 be tested by this method, however, the total cost on a large job 
 will not necessarily be greater than with manual testing. 
 
 (d) Testing of Cross-bonds and Special-Work Jumpers. In 
 
118 
 
 ELECTROLYSIS SURVEYS 
 
 "D 
 Jl 
 
 | 
 
ELECTROLYSIS SURVEYS 119 
 
 addition to testing the joints discussed above, it is important also 
 to test the condition of cross-bonds between rails and of jumpers 
 spanning special work. This can perhaps best be done by means 
 of a low reading voltmeter having two ranges from .01 to one volt, 
 the test being made by going along the track and measuring the 
 potential difference between the various rails at frequent intervals, 
 and also across various sections of special work. 
 
 2. Measurement of Leakage Resistance between Tracks and 
 Underground Structures. 
 
 (a) Importance of Tests of Roadbed Resistance. The determina- 
 tion of the average resistance of the leakage path between railway 
 tracks and surrounding earth is often very desirable, particularly 
 where it is necessary to determine what overall potential drops 
 may safely be permitted in the track return. It will be evident 
 that if the resistance of the leakage paths is very high, it will be 
 safe to allow higher potential drops in the track than if the leakage 
 resistance be low, although the voltage drop which may be con- 
 sidered safe is not directly proportional to the average resistance 
 of the leakage path. 
 
 (b) Differential Method of Measuring Roadbed Resistance. Fig. 
 23 illustrates the method employed for making measurements on 
 roadbeds where it is found impracticable to isolate a limited section 
 of the track. After the car traffic has been withdrawn for the 
 night, a portable storage battery is connected, as shown, between 
 the four rails of the track and a fire hydrant on a relatively large 
 main. An ammeter and a regulating resistance are included in 
 the circuit. A ten volt storage battery or a low voltage generator 
 is employed for this purpose and a constant current of from twenty 
 to forty amperes is maintained during the period of the test. The 
 current entering the rails will flow away from the test station in 
 both directions, as shown by the arrows. Leakage will take place 
 to the earth and all of the current will be picked up by the water- 
 piping system and returned to the negative pole of the battery. 
 If now a milli voltmeter be employed to measure the potential 
 drop on a short section of the track at Station A, and again at 
 several thousand feet distant at Station B, the loss of current 
 from the rails between the two stations can at once be determined, 
 provided the rails are of the same weight and resistivity at the two 
 stations, and provided further, that the battery current has re- 
 mained constant. Now, if the potential difference between the 
 section of track under test and the earth at some distance from it 
 
120 
 
 ELECTROLYSIS SURVEYS 
 
 
 
 
 ^ 
 
 111 
 
 
 
 
 
 *1 
 
 
 
 
 a i 
 
 i^MBMM 
 HI^BHHn 
 
 , 1 
 
 
 t-Bi 
 
 I^HHH^H 
 
 MMMMM 
 
 1^ 
 
 
 0) 
 
 
 o 
 
 
 ^ I 1 
 
 
 
 1 rt 
 
 
 II 1 
 
 IH^H^HH 
 H^^HMl 
 
 1 
 
 o 
 
 
 J\J 
 
 MMB.IMMM 
 
 
 
 _J 
 
 ^ 
 
 at 
 
 
 1 
 
 A 
 
 
 
 
 
 
 
 
 
 L 
 
 
 
 
 (J 
 
 
 
 
 
 
ELECTROLYSIS SURVEYS 121 
 
 be measured, the resistance to earth of this section of track can 
 easily be computed. 
 
 While the principle involved in such a measurement is extremely 
 simple, the practical difficulties encountered make accurate and 
 reliable results very difficult of attainment, and it is only by many 
 and repeated measurements that reliable data can be secured. 
 The difference between the currents at Stations A and B is the 
 quantity which must be determined, and as this is usually a small 
 fraction of the total current, even over a distance of one-half 
 mile, a slight error in the measurements would be exaggerated in 
 the result. Errors might result from inaccurate readings or from 
 different rail weights or resistivities. It is necessary, therefore, 
 to make not only one measurement on each of the four rails at 
 both stations, but measurements should be made at several slightly 
 different locations at each station. 
 
 Tn determining the average potential difference between the 
 track and the earth, voltage measurements should be made to as 
 many different underground structures as can be found in the 
 vicinity. Measurements made to the fire hydrants along the 
 track are likely to give erroneous results, due to the gradient on 
 the water main caused by the return current. The most reliable 
 and consistent results are obtained by driving a ground rod into 
 the earth at a distance of not less than 200 feet from the track 
 and measuring the potential difference between it and the track 
 with a high resistance voltmeter. 
 
 (c) Isolation Method of Measuring Roadbed Resistance. When 
 it is desired to make measurements in localities where no piping 
 systems exist, the method just described cannot be employed. 
 These roadbeds are usually of open construction and it is there- 
 fore a comparatively simple matter to remove the joint plates 
 and bonds from four joints, thus isolating a section of track on 
 which accurate and reliable measurements can be made. Fig. 
 24 shows the arrangement of the apparatus for this test. A 
 section of track from 100 to 500 feet in length is isolated from the 
 remainder of the track network by removing the bonds and joint 
 plates as shown. All cross bonds between this test section and 
 the adjacent track must also be cut. A battery of three or four 
 dry cells is connected between the test section and the remainder 
 of the track network, which, being of great extent, is considered 
 as a remote ground of negligible resistance. A low-reading am- 
 meter and a voltmeter give the current flowing and the potential 
 difference between the section of the track under test and the 
 
122 ELECTROLYSIS SURVEYS 
 
 remote ground, and from these data the resistance to earth is 
 easily and accurately calculated. 
 
 By taking several hundred feet of track, the effect of the short 
 leakage paths at the ends of the section is practically eliminated. 
 
 The resistance so found is for a single-track roadbed but in the 
 open type of construction the resistance to earth is concentrated 
 largely in the ties and therefore the resistance of double track can 
 be taken as one-half that of single track. This is not true when 
 the rails are imbedded in earth or concrete. In this case the re- 
 sistance of a double track may be taken as about seventy per 
 cent of that of a single track if only approximate results are re- 
 quired. This method of measuring roadbed resistances necessi- 
 tates working at night, as does the differential method, since it 
 usually requires several hours to remove and replace the bonds 
 and joint plates on four joints. 
 
 3. Location and Testing of High-Resistance Joints in Pipes. 
 
 In making electrolysis surveys, it is often necessary to determine 
 whether or not there are any considerable number of high resist- 
 ance joints in a given portion of a pipe network. This has been 
 a particularly important test in making investigations of joint 
 electrolysis in pipe systems, and may often be useful in determin- 
 ing upon the method of protection to be used in particular cases. 
 High-resistance joints may be most conveniently located by means 
 of potential drop measurements along the pipes. The method 
 usually followed is to drive bars down until they come in contact 
 .with the pipe and measure the potential drop on the pipe at such 
 points, the spacing of the points being usually about 100 feet. 
 A series of such measurements is made throughout the entire 
 length of the pipe and the relative magnitudes of the voltage drops 
 on adjacent sections would indicate which, if any, is affected by 
 high resistance in the pipe line. When it has been determined 
 that any particular hundred-foot length includes one or more 
 high resistance joints, this section can be further subdivided by 
 exactly the same procedure until a relatively high drop is obtained 
 between two points less than a pipe length apart, which must in- 
 clude a high resistance joint. By comparing the drop across the 
 the high resistance joint with the drop in a measured distance on 
 continuous pipe, the resistance of the joint in terms of equivalent 
 feet of pipe can be obtained. 
 
ELECTROLYSIS SURVEYS 123 
 
 4. Tracing the Source of Stray Currents. 
 
 Conditions are often encountered in which stray currents on 
 pipe networks may come from any one of two or more railway lines, 
 and it is important to determine from which line the current is 
 derived. This can be determined in either of two ways. One 
 method is to connect a measuring instrument of the recording type 
 to the pipe under test, which may be connected either to indicate 
 the current flow along the pipe or the potential difference between 
 the pipe and the earth. With the instrument thus connected, a 
 record is obtained, while all railway systems are operating under 
 normal conditions. Then one of the railway systems is shut 
 down for as long a period as practicable. If the shutting down of 
 the plant makes a marked difference in the record, it is an indica- 
 tion that a large part of the stray current at least comes from that 
 particular point. By shutting down the different systems in 
 rotation, a fairly definite knowledge of the source of the stray 
 current may be obtained. Sometimes it will be found that the 
 shutting down of one plant increases the current flow in one 
 direction, while shutting down another plant may give rise to a 
 large current flow in the opposite direction, both currents being 
 larger than when both plants are running. This will indicate that 
 the stray current from the two systems tend to neutralize each 
 other, thus giving rise to better conditions in certain localities 
 than those which prevail when either system is operating alone. 
 
 The other method of tracing the source of stray current in any 
 particular case consists in the use of two or more recorders, one 
 of which makes a graphic record of the current or voltage, the 
 source of which is to be determined, while the others are used to 
 make simultaneous records of the loads on the various power 
 supply stations which may possibly affect the area in question, 
 or more particularly the loads on certain feeders from those sta- 
 tions. In most cases there will be sufficient similarity between the 
 chart of the stray current and some one of the feeder or station 
 load charts to establish quite definitely the source of the stray 
 current. 
 
 5. Location of Unknown Metallic Structures or Connections. 
 
 It is often desirable to locate metallic connections between pipes 
 and various other structures, such as railway track returns which 
 may often exist without the knowledge of either the pipe or rail- 
 way company. Two methods are available for doing this: One 
 consists in connecting an external electrical circuit between 
 
124 ELECTROLYSIS SURVEYS 
 
 convenient points on the pipe system and railway system, and 
 sending between them either an alternating current of audible 
 frequency or a direct current interrupted, at audible frequency. 
 An exploring coil is then carried along the pipe system in such 
 position that the alternating or pulsating magnetic field produced 
 by the current superposed on the pipe current will induce an elec- 
 tromotive force in the coil. This can be made audible by the use 
 of a telephone receiver. By this instrument, the path of the 
 current can be traced and in most cases the location of concealed 
 connections to the pipe can be determined. The method works 
 very satisfactorily on relatively simple pipe networks, but in very 
 complicated systems where there are a great many pipes laid in 
 the street it becomes relatively difficult to trace out any particular 
 structure. 
 
 A method that has been more recently developed and which is 
 considerably more simple than the above, consists in doing away 
 with the additional current superposed on the pipe network, and 
 using the exploring coil and telephone to listen to the commutation 
 note in the railway current carried by the pipe. This method is 
 much to be preferred where the pipe currents are large enough to 
 give sufficient sensitivity. In some cases, however, where the 
 currents on the pipe are very small, the first method may have to 
 be resorted to. 
 
 in. INTERPRETATION OF RESULTS OF ELECTROLYSIS 
 
 SURVEYS 
 
 No definite rules of procedure can be laid down for the interpre- 
 tation of the results of electrolysis surveys that can be used 
 except by engineers thoroughly familiar with all the factors in- 
 volved. The significance of any particular set of readings is so 
 dependent upon other conditions that all factors must be taken 
 into account or else the conclusions are likely to be in error. 
 However, it is desirable to point out certain principles that must 
 be kept in mind even by the experienced engineer in order to 
 arrive at correct conclusions. 
 
 A. INTERPRETATION OF POTENTIAL MEASUREMENTS 
 1. Maximum Voltages and Track Gradients. 
 
 These measurements, when considered in the light of a full 
 knowledge of all conditions, give valuable data on the condition 
 of the railway track system and the concentration of return current 
 on certain sections of track. They also are valuable when con- 
 sidered in the light of the load on the different lines, as they offer 
 
ELECTROLYSIS SURVEYS 125 
 
 a fairly accurate indication of the track losses and the necessity 
 for the use of additional track feeders. When such potential 
 measurements are taken over relatively short lengths of track, such 
 as 1,000 or 2,000 feet, the comparison of such measurements on 
 adjacent sections of track will often reveal bad places in the track 
 that are in need of rebonding.- 
 
 2. Potential Difference Measurements. 
 
 Potential difference readings between pipes and railway tracks 
 and between various underground structures are not a quantita- 
 tive measure of the danger to the affected structures. These 
 readings are valuable in pointing out the general areas in which 
 trouble may be expected to occur and in which more careful 
 search may be made if desired. They are, however, of qualitative 
 significance only. The current leaving a structure for the earth 
 in any locality, which is the real cause of the electrolysis damage, 
 is a function not only of the potential differences but of the re- 
 sistance of the earth paths. This has been shown to vary through- 
 out extremely wide limits, so that the measurement of potential 
 difference gives no definite quantitative measurement of the 
 extent of the hazard to the pipes. Such measurements are very 
 valuable and have an accurate quantitative significance, however, 
 when used to determine the relative electrolysis conditions under 
 different systems of mitigation. If, for example, under a given 
 set of conditions a considerable number of potential difference 
 measurements are made between the various underground struc- 
 tures and then a change is made in the mitigative system, and the 
 same measurements repeated, the two sets of readings may be 
 used to represent the comparative hazard in the two cases. This 
 is true only if the mitigative measures under test are applied 
 exclusively to the railway return system. 
 
 High potential differences between gas and oil pipes and other 
 metallic structures with which they may come in contact are 
 objectionable especially in confined spaces, such as basements 
 in which explosive mixtures may be encountered. This is because 
 a transient contact between the two structures may cause an arc 
 which may result in fire or explosion. 
 
 B. INTERPRETATION OF CURRENT MEASUREMENTS ON 
 
 UNDERGROUND STRUCTURES 
 1. Relation of Stray Current to Corrosion. 
 
 The magnitude of the current on an underground structure does 
 not alone afford a measure of the total injury, to the structure. 
 
126 ELECTROLYSIS SURVEYS 
 
 If all the current that flows on the pipe is discharged directly 
 into the earth, then the total corrosion will be approximately 
 proportional to the current flow. Even here, however, the rate 
 of damage to the pipes is not only a function of the total weight of 
 metal corroded away, but of the distribution of such corrosion as 
 a result of pitting or of localized discharge from one system to 
 another where they approach close to each other. Further, if 
 there are metallic connections either known or unknown between 
 portions of the pipe networks and the railway tracks, which carry 
 off a large part of the current on the pipe through metallic paths, 
 the total amount of corrosion cannot be determined by measure- 
 ment of the current flow. For this reason current measurements 
 on pipes should likewise be regarded as having only a qualitative 
 significance in so far as any absolute hazard to the pipes is con- 
 cerned. If, however, the pipes have no drainage connections 
 and changes are made in the railway track network, the corre- 
 sponding changes in the currents on the pipes may, if a sufficient 
 number of readings have been taken, indicate the relative im- 
 provement in the electrolysis conditions. 
 
 2. Relation of Current to Fires and Explosions. 
 
 In interpreting the significance of current measurements on 
 gas or oil pipes, due account should be taken of the possibility 
 of fires and explosions due to arcs formed either when pipes are 
 disconnected, or when pipes make transient contact in confined 
 places such as cellars. No definite information is at present 
 available as to what limiting currents on such pipes may be 
 considered safe, but it is generally recognized that the presence 
 of currents on gas and oil lines is more objectionable than in the 
 case of other pipes. 
 
 C. INTERPRETATION OF MEASUREMENTS OF CURRENT 
 FLOWING FROM STRUCTURES TO EARTH 
 
 The only accurate criterion of electrolysis damage is the in- 
 tensity of current flow to earth at any point on the pipe or cable. 
 If an accurate measure of this current flow from the pipe at any 
 point could be made, it would come nearer giving a true indication 
 of electrolysis conditions than any other measurement. At the 
 present time there is no practical means available for making such 
 measurements. The development of a simple, inexpensive and 
 accurate means for measuring such currents locally, constitutes 
 one of the chief needs in the field of electrolysis testing at the 
 present time. 
 
ELECTROLYSIS SURVEYS 127 
 
 D. USE OF REDUCTION FACTORS 
 
 In many cases it is not practicable to take readings of current 
 and potential at any point over a sufficiently long time to get all 
 day average values of the readings at that point. Such readings 
 should always be taken for as long a time as circumstances permit, 
 but in making electrolysis surveys, it is usually necessary to 
 take a large number of readings scattered over a wide area so 
 that some of the readings can be continued only for a compara- 
 tively short time. Such short-time readings cannot, in general 
 be used directly as a basis for determining electrolysis conditions 
 and in order to interpret properly the results of the survey, the 
 readings must be reduced to some common basis, as for example, 
 either the twenty-four-hour average, the operating-day average, 
 or the average for the hour of the peak load. Each of these bases 
 has certain advantages and disadvantages depending partly on 
 the individual conditions, and the method of procedure will often 
 differ, depending on the method to be followed in interpreting 
 the results. All are affected by such factors as rush or light days, 
 unusual weather conditions, electric heaters in cold weather, 
 morning and evening peak loads, and other causes, and these 
 factors must be considered. 
 
 The great unreliability of short-time readings for determining 
 electrolysis conditions is especially noticeable when comparing 
 the load curve of a line having a 5, 10, or 15 minute schedule 
 with that of hourly interurban service, or when comparing that 
 of a station having a 45 per cent load factor with one having a 
 load factor of 10 per cent. Because of this great variation and 
 uncertainity in short time measurements and for the purposes of 
 interpretation and comparison, it is desirable that long time 
 readings be obtained, but if this is impossible, all short-time read- 
 ings should be reduced to values for some representative period, 
 preferably the twenty-four hour average. 
 
 Experience shows that in the majority of cases, short-time 
 readings of from 15 minutes to an hour, taken on a city network 
 between the hours of 10 A. M. and about 4 P. M., approach rather 
 closely the twenty-four-hour average values, and it is found per- 
 missible to neglect the use of reduction factors in connection 
 with readings taken during this period of the day. When, how- 
 ever, readings are taken at any time during the morning or evening 
 peak, or after nine or ten o'clock at night, it is necessary to use a 
 proper reduction factor if anything like reliable conclusions are 
 to be reached. In general, it seems preferable to reduce such 
 
128 ELECTROLYSIS SURVEYS 
 
 readings to the all-day average basis, rather than to the operating- 
 day average since the operating day varies in length in different 
 cities. 
 
 E. EFFECT OF REVERSALS OF POLARITY 
 
 Throughout a large portion of the territory served by a grounded 
 railway system, it will be found that the potential differences 
 between pipes and earth frequently reverse in direction, the pipes 
 becoming alternately positive and negative to earth with periods 
 varying from a few seconds to several minutes or even longer; 
 and special consideration has to be given to measurements in such 
 places in order that even an approximate estimate of their sig- 
 nificance can be made. In general, four different classes of con- 
 ditions have to be recognized in interpreting these measurements 
 as follows : 
 
 1. Polarity of Pipes Always the Same. 
 
 If the pipes are always of the same polarity, as, for example, 
 always positive to surrounding structures, it is, of course, the 
 arithmetical average value that should be used in judging the 
 significance of the readings. 
 
 2. Polarity of Pipes Changing with Long Periods of Several Hours. 
 
 If the pipes at any point are continuously positive for a period 
 of several hours, and then of opposite polarity for a succeeding 
 period of 'some hours, a condition which frequently exists in 
 localities where a substation is operated during only a portion 
 of the day, there will in general, be relatively very little protective 
 effect due to the period when the pipe is negative or neutral to 
 earth, and the actual corrosion is most nearly indicated by the 
 arithmetical average value of the voltage or currents during the 
 hours in which the pipe is positive to earth, this, average, of 
 course, being reduced to the twenty-four-hour average basis. 
 Thus, if a given pipe is found to be positive to the earth or other 
 neighboring structures by a given amount for a period of twelve 
 hours, and either negative or at zero potential for the remaining 
 twelve hours of the day, the actual amount of corrosion that would 
 occur would undoubtedly be nearly equivalent to that which 
 would result if the potential at the same point was maintained 
 half as great for the full twenty-four hours. 
 
 3. Polarity of Pipes Reversing with Periods of Only a Few Minutes. 
 
 Where the polarity of the pipes reverses with a period of only a 
 few minutes, it has been shown by extensive experiments that the 
 
ELECTROLYSIS SURVEYS 129 
 
 corrosive process is in large measure reversible, and the actual 
 amount of corrosion comes more nearly being proportional to the 
 algebraic average of the applied potential than it is to the arith- 
 metical average during the total time the pipe is positive. In 
 all cases, therefore, where the polarity of the pipe is continuously 
 reversing and the period of reversal does not exceed five or ten 
 minutes, the algebraic average of the voltages or currents should 
 be given far greater weight than the arithmetical average values 
 during the positive period. 
 
 4. Polarity of Pipes Reversing with Periods of From Fifteen 
 Minutes to One Hour. 
 
 Under these conditions, neither the algebraic nor the arith- 
 metical average of the applied potential or current flow gives an 
 accurate index of the amount of corrosion. For the shorter period 
 the algebraic average comes more nearly being the proper criterion, 
 while as the period increases in length the arithmetical average 
 tends to give a better indication of the extent of the resulting 
 corrosion. However, even where the period of reversal is as long 
 as one hour, the corrosive process is, under most conditions, to a 
 considerable extent reversible and some allowance in interpreting 
 the results should be made. 
 
 IV. SELECTION OF INSTRUMENTS 
 
 In this section descriptions are given of the apparatus and 
 tools which are essentially special for electrolysis work. The 
 tools ordinarily used for handling wires and making good contacts 
 in electrical work will also be needed, but no special description 
 or listing of them seems to be necessary in this place. 
 
 A. PORTABLE MEASURING INSTRUMENTS 
 
 The portable measuring instruments required in electrolysis 
 survey work include voltmeters, milli voltmeters, and ammeters. 
 Separate instruments of each kind, can -of course, be carried, but 
 it will usually be found more convenient to employ the special 
 portable instruments which have been designed particularly for 
 this work. Three such instruments which the Weston Electrical 
 Instrument Company manufacture for this class of work are as 
 follows : 
 
 Model 1, combination millivoltmeter and voltmeter, has 
 its zero in the center of the scale, and reads in both directions. 
 Ranges of 5, 50, and 500 millivolts and of 5 and 50 volts are 
 convenient. It is made with a specially high resistance of 
 
130 ELECTROLYSIS SURVEYS 
 
 from 500 to 600 ohms per volt so that the 5 millivolt range 
 has a resistance of about 3 ohms. These high resistances 
 minimize errors due to resistances of leads or contacts. For 
 work on the street, a dust-proof case should be specified. 
 Ordinary switchboard shunts provided with binding posts 
 and adjusted for 50 millivolts may be used to make this instru- 
 ment serve as an ammeter. Convenient ranges for these 
 shunts in electrolysis work are 5, 50, and 500 amperes. 
 
 Model 56, combination volt-ammeter has its zero in the 
 center of the scale and reads in both directions. Ranges of 
 10, 50, and 500 millivolts, 5 and 50 volts and up to 100 am- 
 peres are convenient. 
 
 Model 322, millivoltmeter, has the zero at the left of the 
 scale and a full scale deflection of one millivolt. Owing to 
 the low range and extremely light movement it must be used 
 with a great deal of care. It is useful for determining very 
 low differences of potential such as drops along short sections 
 of pipe or feeder for determining current flow. 
 
 The center scale feature referred to in the description of these 
 instruments is an important one in electrolysis work, as it is not 
 always possible to determine in advance the direction of current 
 or potential, and readings may also vary from positive to negative 
 values during the making of observations at many testing points. 
 When simultaneous readings have to be taken at two or more 
 testing points, it is important to use similar instruments at all 
 points. If dissimilar instruments are used, their periods may 
 differ and with the fluctuating voltages and currents encountered 
 i|i much of this work, accurate simultaneous measurements 
 cannot be made unless the instruments used have the same periods. 
 
 B. RECORDING INSTRUMENTS 
 
 Recording measuring instruments are usually arranged to give 
 24-hour records without change of chart. By using a sensitive 
 millivoltmeter in the recording instrument and providing it with 
 a number of voltage ranges as well as with suitable shunts, a 
 single instrument can be- made available for taking all of the 
 voltage and current readings required in electrolysis work. The 
 type of Bristol recording instruments used for electrolysis work 
 makes a record upon a smoke-chart which has to be treated sub- 
 sequently with a fixative supplied with the instrument. The 
 Bristol instruments are regularly made with a clock supplied with 
 a changing lever so that the disk can be made to rotate either in 
 one hour or twenty-four hours. 
 
 The Esterline recorder uses ink and a roll chart and may be 
 obtained with a large range in chart speeds. This is particular y 
 
ELECTROLYSIS SURVEYS 131 
 
 valuable in the detailed study of changes which take place during 
 short intervals and where a record covering more than one day is 
 required. The clock will operate for a week with one winding. 
 Several other manufacturers make portable recorders suitable for 
 some electrolysis measurements. In either type of instrument, 
 center scale zeros should be called for so that variations between 
 positive and negative values will be recorded on the chart. 
 
 V. RECORDS AND REPORTS 
 
 A. GENERAL DISCUSSION 
 
 Much detailed information is necessarily gathered in the course 
 of an electrolysis survey. It is desirable to prepare in advance of 
 the work for the convenient recording of these data upon suitably 
 arranged testing sheets, which either have upon one line or upon 
 one sheet, as may be necessary, all of the data collected at any 
 stated testing point during a single period of observation. Several 
 typical data sheets prepared for recording observations made 
 upon piping and cable systems are given in the appendix to this 
 report as suggestive of possible arrangements for report sheets. The 
 data thus collected can usually be best arranged for study if they 
 are transferred to a map showing the system or systems included 
 in the tests, and indicated thereon either in numerical form or 
 through some graphical representation. It is desirable to indicate 
 positive and negative relations by making records on the maps in 
 different colors. 
 
 Apart from the data obtained through observations in the work 
 of the electrolysis survey, the records obtained relating to the 
 systems under observation should include the following: 
 
 B. ELECTRIC RAILWAYS 
 
 1. Maps showing locations of sources of power supply, tracks 
 and negative feeders and other connections between bus-bar and 
 track; also locations of positive feeding connections to trolley 
 and all trolley feeder sections. 
 
 2. Information regarding magnitude and distribution of load 
 shown by a "spot map" of the railway system. 
 
 3. Information as to size of rails, methods of bonding and 
 standards of bond maintenance. 
 
 4. Information as to any direct ground connections applied to 
 the railway return system, and any special track features which 
 may affect the flow of stray currents. 
 
132 ELECTROLYSIS SURVEYS 
 
 C. PIPING SYSTEMS 
 
 1. Maps showing all main pipe lines and branches (except ser- 
 vice connections) and sources of water, gas, etc., from which the 
 piping systems are supplied. 
 
 2. Information as to sizes of pipes, and metals of which they are 
 composed, and details of the standard methods of joining main 
 and branch line pipe sections. 
 
 3. Information as to -method of joining service connections to 
 main supply pipes including metals used for the building connec- 
 tion pipes and the depth to which such connections are buried. 
 
 4. Location and description of any protective devices such as 
 insulating joints; also any drainage connections which may have 
 been made a part of the piping system. 
 
 5. Information as to methods of attachment and construction 
 employed in carrying pipes over highway or railway bridges or 
 under water courses, swamps, etc. 
 
 D. CABLE SYSTEMS 
 
 1. Maps showing locations of all conduit routes and giving 
 number and sizes of cables in place therein or the total cross- 
 section of lead sheaths expressed in equivalent copper, also loca- 
 tions of power stations, sub-stations or other centers from which 
 cables radiate. Complete data on bonding practice should be 
 secured. 
 
 2. Locations, routes and sizes of all drainage connections at- 
 tached to cable systems, also locations of all insulating joints in 
 cable systems, of any junipers which may be run to establish a 
 metallic circuit across an insulated gap in the cable system and of 
 any conductors run to reinforce the carrying capacity of the cable 
 system for stray currents. 
 
 3. Information as to methods of attachment and construction 
 employed in carrying cables over highway or railway bridges or 
 under water courses, swamps, etc. 
 
 E. BRIDGES AND BUILDINGS 
 
 1 . Locations of structures with respect to electric railways. 
 
 2. Information as to methods of construction employed in 
 carrying electric railways, pipes and cables across bridges and 
 particularly as to whether any of these other structural systems 
 make electrical contact with the metal structure of the bridge. 
 
 F. GENERAL CONDITIONS 
 
 1. Maps showing locations of water courses, swamps, and other 
 features tending to produce locally, earth of high unit conductivity. 
 
ELECTROLYSIS SURVEYS 133 
 
 2. Records of electrical resistance of soil samples representative 
 of the area. 
 
 3. Records of experience obtained in the use of different metals 
 for pipes, etc., in the soils of the area. 
 
 It is desirable that in the preparation of records and of reports, 
 consideration be given to the necessity of their perpetuation. All 
 records which will be of permanent value in connection with the 
 continued study of electrolysis conditions in any particular area 
 in order to make sure that injurious changes in conditions do not 
 occur, should be prepared in a permanent form capable of with- 
 standing considerable handling. 
 
 VI. TABLES 
 
 The tables in the appendix are to be used for calculating the 
 current flow in different kinds and sizes of pipes from the measure- 
 ment of the millivolt drop on a definite length of pipe. These 
 tables were prepared by the U. S. Bureau of Standards from a 
 large amount of test data taken on representative specimens of 
 pipe from a number of different manufacturers. 
 
 The figures for wrought iron pipes represent the results of tests 
 made on 86 separate specimens of pipe. Those for steel pipe are 
 based on tests of 64 specimens, and those for cast iron are based 
 on test data from 22 specimens of pipe from a number of different 
 foundries. 
 
 The tables for lead pipe are based on test data taken on 27 
 specimens ranging from one-fourth to two inches in diameter, 
 all of which, however, were obtained from one manufacturer. It 
 is believed, however, that these figures can be used for all lead 
 service pipes with sufficient accuracy for most practical purposes. 
 
 These tests showed that the resistance of cast iron, wrought 
 iron, and steel pipes can be estimated from these tables with an 
 accuracy of at least 10 per cent, and in most cases the results will 
 be even better than this. The tests showed an average resistivity 
 for steel pipe of 215.8 microhms per pound-foot, for wrought iron 
 pipe 209.3 microhms per pound-foot, and for cast iron the figure 
 is 1,227 microhms per pound-foot. These average values have 
 been used in the calculation of the tables. 
 
 Tables for lead sheathed cables have not been included in this 
 report, owing to the large number of different sizes and thicknesses 
 of sheaths used for signal and power cables, as well as a variation 
 in resistivity with different sheath compositions. 
 
CHAPTER 4 
 
 EUROPEAN PRACTICE 
 A. GENERAL 
 
 In the study of the practice followed in European countries for 
 handling the problem of electrolysis, it has appeared impossible 
 to secure reliable and satisfactory information merely by cor- 
 respondence and consultation of published reports and regulations. 
 Moreover, the several independent reports made by American 
 investigators before the foundation of the American Committee, 
 were made from the standpoint of some special industry rather 
 than from the broad and comprehensive viewpoint of this Com- 
 mittee. Under these circumstances the necessity for an inde- 
 pendent personal investigation was evident. 
 
 The Chairman of this sub-committee, after consultation with 
 its members and with the general Chairman, decided to visit 
 several European countries during the summer of 1914. Informa- 
 tion concerning important foreign cities and authorities, and 
 papers, suggestions and references were obtained from Mr. H. S. 
 Warren and the late Prof. Albert F. Ganz. Also the officials of 
 the Bureau of Standards were consulted when the field of inquiry 
 and special points to be looked after were carefully discussed. 
 An effort to have the Bureau of Standards appoint a representative 
 to join trie party failed on account of their extensive engagements. 
 However, the party included an engineer thoroughly conversant 
 with electrolysis measurements and surveys. 
 
 The visiting Committee spent June and July in its investigation, 
 covering Germany, Italy, France, and England. In each country 
 an effort was made to take measurements and to collect data and 
 surveys, also to interview the most prominent people in each of the 
 different interests affected by the problem of electrolysis. In 
 each case extended conferences were held with the engineers most 
 familiar with the problem and its details, either in their capacity 
 of specialized consulting engineers, or as officials of corporations 
 or public authorities directly concerned in the surveys, disputes, 
 or administrative measures relating to electrolysis. 
 
 After this investigation of 1914, the conditions which existed 
 
 during the War and later, made it impossible to collect any further 
 
 information until the winter of 1920-21, and even then only 
 
 fragmentary reports of later developments were obtained from 
 
 134 
 
EUROPEAN PRACTICE 135 
 
 Great Britain alone. However, it is believed that the same cir- 
 cumstances have retarded development so that the conditions 
 observed in 1914 correspond substantially with those existing at 
 the present time. It should be borne in mind, however, that 
 references in this report to the current status of committees or 
 commissions, and of legislation or litigation, will unless otherwise 
 noted, refer to the ;ummer of 1914. 
 
 The results of the Sub-Committee's investigations are summar- 
 ized in the paragraphs immediately following, classified by prin- 
 cipal topics. This is followed by statistical information, details of 
 design and operation, and rules and regulations in effect in different 
 European countries. 
 
 B. LAWS AND REGULATIONS 
 1. Germany. 
 
 There are no laws specifically relating to electrolysis, and so 
 far as could be ascertained, there are no local ordinances dealing 
 with this subject. The common law of most of the states pre- 
 scribes that all of the conditions under which a corporation is to 
 operate must be contained in the original .grant and any later 
 grants for extensions. The law requires that due publicity be 
 given to any request for a franchise or for extensions of lines, so 
 as to afford all parties who may be affected an opportunity to 
 place on record any limitation they may desire to propose, or to 
 request provisions concerning possible damage, before the conces- 
 sion is granted to the applicant. Hence, a pipe owning company 
 organized subsequently to the existence of an electric railway is 
 held to have assumed the risks existing at the time of its organiza- 
 tion, and it therefore cannot claim damages from this railway on 
 account of electrolysis unless the original franchise to the railway 
 contained a clause regarding such damage. 
 
 The foregoing applies to private corporations. Municipal 
 corporations, on the other hand, do not assume the legal obligation 
 to protect existing systems against the effects of electrolysis. 
 In such cases, pipe owning companies already in existence are 
 deprived of the privilege of demanding that protection against 
 possible future damage which would be accorded them in the 
 case of a new privately owned railway company. 
 
 Municipalities, however, for their own new railway construction 
 as well as for new extensions of the railways of private companies, 
 always prescribe that they be constructed and operated in accord- 
 ance with existing technical standards. The recommendatioias 
 
136 EUROPEAN PRACTICE 
 
 of the German Earth Current Commission are recognized as the 
 existing technical standards in matters relating to electrolysis 
 and in this manner they have assumed almost the importance 
 of law. These regulations are being generally incorporated in 
 contracts for new enterprises or extensions, and in such cases 
 they do substantially attain the force of law. 
 
 (a) Commission Recommendations. The work of the German 
 Earth Current Commission is described in detail in another place, 
 and a translation of the complete text of its recommendations is 
 given later. The recommendations of the Commission were 
 adopted by the German Electrotechnical Society in 1910. In ab- 
 stract the recommendations prescribe the following : 
 
 In large cities, and in general in urban networks and for a 
 distance of 2 km. (1.24 miles) beyond, the overall rail drop is 
 limited to 2.5 volts. Outside of this zone, and in general in small 
 places or for single lines, the potential gradient is limited to 1 volt 
 per km. (1.6 volts per mile). Exceptions are made for roads 
 operating only a few hours in the day. Bonds must not increase 
 the resistance of tracks over 20 per cent; they must be tested 
 yearly, and when a bond shows a resistance higher than ten 
 meters (11 yards) of rail it must be repaired. Connections to 
 pipes are prohibited. Bare return feeders are not allowed. 
 Pilot wires are prescribed. The voltage limits given are inter- 
 preted to be the average for the entire daily period of operation, 
 usually 18 to 20 hours in 24 hours. If measurements are not 
 actually taken over the entire period they are corrected to obtain 
 a figure corresponding to this average. 
 
 2. Italy. 
 
 The Government has not enacted any law affecting the operation 
 of electric railways in relation to electrolysis problems, nor has 
 any municipality issued regulations on the subject. 
 
 3. France. 
 
 Regulation in France is based on a Ministerial decree of 
 March 21, 1911, establishing the technical conditions which 
 electrical distribution systems must satisfy in order to conform 
 to the Law of June 15, 1906. A translation of the text of this 
 decree is given later. Briefly the requirements are : 
 
 That the maximum voltage drop in rail returns of electric 
 tramways shall not exceed one volt per kilometer (1.6 volts per 
 mile) ; an exception is made for locations where metallic masses, 
 such as pipe networks, do not exist. Bonds must be kept in the 
 
EUROPEAN PRACTICE 137 
 
 best possible condition; the resistance of a bond must not be 
 greater than ten meters (11 yards) of normal rail. Return 
 feeders must be insulated. Periodic tests must be made and 
 recorded on a register subject to inspection by the control service. 
 No definition is given of the time element in the measurement 
 of maximum drop, except that it is stated that it must be the 
 average for the normal schedule. 
 
 4. Spain. 
 
 A translation of sections of the Law of March 23, 1900, relating 
 to electric railway return circuits is given later. Briefly, this 
 law requires the overall voltage not to exceed seven volts, specifies 
 bonding and cross-bonding, and where necessary reinforcements 
 of rail conductivity. 
 
 5. Great Britain. 
 
 Control of electrolysis matters in Great Britain is obtained 
 through regulations made by the Board of Trade under the 
 provisions of special Tramways Acts or Light Railway Orders 
 authorizing "lines" on public roads; for regulating the use of 
 electric power; for preventing fusion or injurious electrolytic 
 action of or on gas or water pipes or other metallic pipes, structures, 
 or substances ; and for minimizing, as far as it is reasonably prac- 
 ticable injurious interference with the electric wires, lines, and 
 apparatus of parties other than the railway company, and the 
 current therein, whether such lines do or do not use the earth as 
 a return. 
 
 The Board of Trade Regulations were first made in March, 
 1894; they have been revised from time to time, the last revision 
 having been made in September, 1912. The full text of the Regula- 
 tions is given in a following section of this report. In abstract, 
 the regulations prescribe that the overall rail drop shall not 
 exceed seven volts, and there are also clauses concerning track 
 leakage, the measurement of these quantities, etc. The regula- 
 tions also provide for circular returns to be made upon the call 
 of the proper authorities. 
 
 The Board of Trade makes inspections on its own initiative 
 because it is responsible for its rules, which have substantially 
 the force of law; it also investigates complaints. There are no 
 regular inspections on account of the lack of a proper appropria- 
 tion. Most of its information is obtained from the returns; the 
 latest call for a return was issued in 1906. 
 
 The overall voltage is defined, in practice, as an average for 
 
138 EUROPEAN PRACTICE 
 
 about twenty minutes at peak load. This "average" is obtained 
 as the mean between the average of the maxima during the period 
 (disregarding unusually high swings) and the actual average of all 
 measurements. This quantity is usually obtained in practice 
 from inspection of recording instrument charts. 
 
 There are no local ordinances which have the effect of modifying 
 the Board of Trade Regulations. Pipe owning companies cannot 
 recover damages in case corrosion occurs where the Regulations 
 are complied with. This has led to numerous applications to 
 Parliament for special statutory orders fixing responsibility for 
 damage, or special clauses of like import in Acts granting powers 
 to electric railway undertakings. Most of these have been re- 
 fused, but some have been granted. 
 
 It is generally admitted that the Board of Trade Regulations, 
 as originally drawn, were empirical, and that they might be re- 
 modeled with advantage ; but since the only feature of the regula- 
 tions actually rigidly enforced, namely, the limit for overall 
 rail drop, results in substantial immunity, the great difficulty 
 attending revision has not seemed to be justified. 
 
 Railway electrifications, as distinguished from tramways, do 
 not come under the above regulations unless it is especially pro- 
 vided in the Parliamentary Act authorizing the electrification. 
 Recent advices indicate that railway electrifications generally 
 have not been brought under the Regulations. 
 
 C. CONSTRUCTION CHARACTERISTICS 
 
 General types of construction for electric railways and pipe 
 or cable systems and special features characterizing such systems 
 in the various countries visited, are summarized here. Details 
 of construction and statistical tables are given in Figs. 25 to 31, 
 and Tables 7 and 8. 
 
 1. General. 
 
 In large cities the tramways are supplied from a number of 
 substations, as in the municipal systems of Glasgow and Man- 
 chester. In Berlin, particularly the railway system is supplied 
 from a great number of combination light and railway substations 
 feeding limited districts entailing relatively small positive line 
 drop of potential. In England, average feeding distances are 
 said to be from two to three miles (3 to 5 km). 
 
 The ordinary single overhead trolley with the running rails 
 used as some part of the return circuit, is predominantly used in 
 
EUROPEAN PRACTICE 
 
 139 
 
 all of the countries visited. Special features of the return circuit 
 are discussed under appropriate headings below. 
 
 The gas and water piping systems in all of the countries visited 
 
 German Tramway Rails 
 
 Rillenschiene 
 Phonix Profll land la 
 .42.6 and -45/7 
 &eo end 91.9 
 
 Viqnolschiene 
 Special Pro-file for Tramway 
 
 (a) Rilleoscbiene wiih Foot 
 Rsh Plate 
 
 (b) Haarman a piece Pail 
 
 ^ 
 
 1 
 
 % 
 
 II l'j 
 
 
 
 
 o 
 
 o o - ii o o ji o o 
 
 O ij j; O 
 
 
 (c)and(d)haarw)an 2-piece Rail 
 
 Fig. 25. 
 
 did not present any features differentiating them from piping 
 systems in America, so far as the electrolysis problem is con- 
 cerned. In general, pipes are laid in somewhat more shallow 
 trenches than in our northern states, and interconnection between 
 
140 
 
 EUROPEAN PRACTICE 
 
 gas and water systems for heating devices seem to be less common 
 than in America. 
 
 2. Rails. 
 
 In Germany, the common rail weights are 50-60 kg. per meter 
 
 BRITISH TRAMWAY RAILS 
 
 r 
 
 Standard prior to 1908 
 t 
 
 \ Present Standard "Brit Stand." N? 4 
 Bessemer Steel 100- 105 Ibs per yd 
 Fish plates 2' long 635 Ibsper pair 
 
 -inner fish 
 plate 2' long 
 26 Its 
 
 Outer fish 
 
 plate 2' long 
 
 305 Ibs 
 
 Straight track, 110 Ibs per yard 
 "British Standard" Section N? 5 
 
 Curbed track, 116 Ibs. per yard 
 "ritish Standard" Section N ? 5c. 
 
 Fig. 26. 
 
 (101-121 Ibs. per yard) for tramways, and 30-40 kg. per meter 
 (60-81 Ibs. per yard) for interurban lines. In France the ordinary 
 rail weights are 46 to 51 kg. per meter (93-103 Ibs. per yard). 
 In England rail weights vary from 70 to 100 Ibs. per yard (34.7- 
 
EUROPEAN PRACTICE 
 
 141 
 
 49.6 kg. per meter) in the majority of cases. (See Figures 25, 
 26, and 27.) 
 
 3. Rail Bonds. 
 
 Solid copper pin type bonds, usually 1 meter (3.3 ft.) long, 
 
 PAIL WEIGHT DATA 
 
 3000 
 
 2000 
 
 1000 
 
 1000 
 
 750 
 
 500 
 
 250 
 
 40 
 
 tao 
 
 Gf R Mi k M V 
 
 Classified by Rail "types 
 Tptall 
 
 Rillenschien* 5902 Km.'366dMi 
 Viqnolschiene = 1020 Km 634Mi 
 Wecfcseb+eg . 7l4Kir-444Mi 
 
 Rilldnschi 
 
 10 
 
 40 
 
 50 
 
 I I 
 
 UNITED 
 
 Classi 
 
 MTEP KINGDOM 
 fiedby Track Gauges 
 
 *" 
 
 Totals 
 
 '# t \\i and 3' 1rack OfltfM * 29. 6 miles 4a6to 
 3V -\QS66 1700^) - 
 
 4'l 
 5'3 <T 
 
 *Not ploited 
 
 293 8 - 47Z.7 
 404.fi 6513 
 1039.4 ^-1672.4- 
 114.2 " 163-7 
 
 Large Systems other 1han Standan 
 . Cork - 15 miles -2' (( qauqe . 
 
 Birmingham Corp. 16 7 miles 
 
 Bradford-- 100 miles -4* 
 
 ClasdoW - 196-5 mite5 
 Dublin *IOd miles -5f 
 
 _1 - ^ I 
 
 J 1"^ 
 
 40 60 80 
 
 166 
 
 124. 
 
 (603 
 
 401 
 
 100 
 
 IZO 
 
 Fig. 27. 
 
 are most commonly used in Germany and France. The Metro- 
 politan System, in Paris, places the bonds under the base flange 
 of the rail. In England, solid copper pin type bonds', protected 
 
142 
 
 EUROPEAN PRACTICE 
 
 bonds inside of fish plates, and other types familiar in America, 
 are generally used. (See Figure 28, and Table 7.) 
 
 In Germany Thermit welds are used to some extent, and are be- 
 coming more common. In France the rails of the Cie de Omnibus 
 
 TYPICAL RAIL. BONOS - UNITED KINGDOM 
 
 MANCHESTER 
 (Standard) 
 
 GLASGO w 
 
 (Standard) 
 
 Fig. 28. 
 
 Thomson-Houston are welded. In England Thermit welds have 
 been used very extensively, giving good results electrically, but 
 having short life due to mechanical weakness where traffic is heavy. 
 A type of electrically welded continuous rail, very extensively used 
 
EUROPEAN PRACTICE 
 
 143 
 
 TABLE 7 
 RAIL BONDING, UNITED KINGDOM 
 
 
 No. of 
 Undertakings 
 
 Miles of 
 Single track 
 
 Per cent 
 of total 
 (miles) 
 
 Copper Bonds. 
 
 Solid copper, type not specified. . . 
 Flexible copper, type not specified. 
 Crown 3/0 and 4/0 
 
 46 
 9 
 20 
 
 560.0 
 176.0 
 321 
 
 
 Neptune 4/0 
 
 19 
 
 229 2 
 
 
 Chicago 
 
 8 
 
 71 3 
 
 
 Forest City 
 
 5 
 
 37 2 
 
 
 Misc. and type not specified 
 
 15 
 
 406.8 
 
 
 Total, copper bonds only 
 Welded Rails, Etc. 
 Continuous rails, type not speci- 
 fied 
 
 122 
 1 
 
 1801.5 
 17 
 
 47.3 
 
 Yalk cast weld 
 Thermit 
 Thermit and Yalk 
 Thermit and Tudor 
 Thermit and Oxy- Acetylene 
 
 1 
 3 
 1 
 1 
 
 1 
 
 20.0 
 61.6 
 15.9 
 28.0 
 18.0 
 
 
 
 Total, entirely welded 
 Partially Welded. 
 Copper and Thermit 
 Copper and other welded joints . . 
 
 8 
 
 31 
 
 5 
 
 160.5 
 
 1312.4 
 377.3 
 
 4.2 
 
 Total partially welded. . . 
 
 36 
 
 1689 7 
 
 44 3 
 
 Plastic Bonds, Etc. 
 
 Plastic bonds and copper 
 
 3 
 
 147 5 
 
 
 Plastic bonds and Thermit 
 
 1 
 
 12.3 
 
 
 
 
 
 
 
 4 
 
 159.8 
 
 4.2 
 
 in Leeds, and to an increasing extent in Manchester and Glasgow, 
 is giving excellent results, being mechanically strong and providing 
 good electrical conductivity. 
 
 4. Cross Bonds. 
 
 In Germany, cross bonds are used about every ten rails, i.e., 
 every 100 meters (109 yards). In France they are placed every 
 50 to 100 meters (55 to 109 yards) and have the same area as the 
 small rail-bonds. In England cross bonds are generally every 
 forty yards (36.6 meters) and they have the same area as the 
 rail-bonds. (See Fig. 29). 
 
 5. Roadbed Construction. 
 
 The authorities consulted in Germany were of the opinion that 
 
144 
 
 EUROPEAN PRACTICE 
 
 the roadbed constructions used did not tend to affect a reduction 
 of leakage from tracks; a similar opinion was held in England. 
 The types of construction referred to were those illustrated in 
 Figs. 30 and 31. 
 
 CROSS-BONDING DETAFLS, ETC - UNITED KINGDOM 
 
 GLASGOW 
 
 Standard Cross-Bonding 
 
 Single Cross Bondr* 
 
 Rail 
 
 40 yards (2 rail lengths) 
 
 Method of connecting 
 one return cable to 
 track 
 
 LONDON 
 LCC Return Feeder Connections 
 
 Rail 
 
 4-N e OOGO B&S Bonds 
 
 per terminal, about 
 
 34" long,. 
 
 Rail 
 
 Bond Terminal 
 clamped and 
 soldered 
 
 Rail 
 
 Bare Cable-* 
 
 Rail 
 
 Lead Sleeve 
 
 Method of connecting 
 two return cables to 
 track at same point. 
 
 Fig. 29. 
 
 LC. Cable 
 
 A later English report (1920) emphasizes the importance of 
 thorough drainage, as provided by broken stone foundations, as a 
 means for reducing leakage current. The same report gives the 
 following as good average leakage figures for tramway rails in 
 
EUROPEAN PRACTICE 
 
 145 
 
146 
 
 EUROPEAN PRACTICE 
 
 Length of Section 
 
 
 Feet 
 
 Meters 
 
 Per cent Leakage Current 
 
 3,000 
 
 914 
 
 2.5 
 
 4,200 
 
 1,280 
 
 5.0 
 
 6,000 
 
 1,829 
 
 10.0 
 
 7,400 
 
 2,256 
 
 15.0 
 
 8,600 
 
 2,621 
 
 20.0 
 
 9,500 
 
 2,896 
 
 25.0 
 
 TRACK CONSTRUCTION AND RAILS - GERMANY 
 
 Typical Construction for paved street 
 
 STRASSBURG 
 Haarman. 3 piece Rail, and foot plate 
 
 Fig. 31. 
 
 direct contact with soil. The table is based on equal unit loading 
 for various lengths of section. 
 
 Leakage current is proportional to the square of the length, and 
 direcfty proportional to overall voltage. 
 
 The report also states that tests on railway tracks laid on 
 
EUROPEAN PRACTICE 147 
 
 wooden sleepers with broken stone ballast show about 25 per cent 
 of the leakage for tramway rails. 
 
 Tests made in Strassburg indicated that leakage currents were 
 fifty per cent greater in summer than in winter when the ground 
 was frozen. In snow storms, however, the winter leakage currents 
 were increased as the cars were using more current. 
 
 6. Feeders. 
 
 Insulated return feeders are used almost universally in Germany. 
 In Berlin and Hamburg these return feeders are of the same num- 
 ber and size as the positive feeders, but generally in other towns 
 the return feeders are of smaller cross-section. Separate feeders 
 are generally used, but not exclusively, as feeders with resistance 
 taps are used in some cases. Formerly there were cases of 
 feeders tapping at several points but important cases have been 
 corrected by the insertion of resistances. No design data for 
 feeder resistances were obtained. The Hamburg installation of 
 insulated feeders was made prior to the formation of the German 
 Earth Current Commission. It gave valuable information in 
 guiding the recommendations of the Commission. 
 
 Return feeders are not used for tramways in Italy; in large 
 installations bare returns are generally used. In France most 
 tramways have but one feeding point to the rails. Insulated 
 return feeders are used for the conduit tramways in Paris, but 
 little elsewhere. 
 
 In England insulated return feeders are used wherever they are 
 necessary to bring the rail drop within the B. O. T. regulations; 
 separate feeders are generally used. There is very little overhead 
 feeder line construction in Germany, and almost none in England. 
 
 In Germany insulated negative feeder systems have been care- 
 fully calculated in recent installations. In England they are 
 calculated only in the larger, well supervised systems; elsewhere 
 they are installed by "cut-and-try" methods. The same grade 
 of insulation is usually provided for both positive and negative 
 feeders. The distinction between copper which merely parallels 
 the rails, and feeders which are intended to reduce overall poten- 
 tials by maintaining equipotential points in the rail network, is 
 clearly understood in Germany and England. 
 
 Recent reports concerning heavy railway electrifications in 
 England indicate that insulated return feeders are not generally 
 used on such systems, possibly because they are not limited to the 
 overall voltages of the Tramway regulations. The usual practice 
 
148 EUROPEAN PRACTICE 
 
 is to locate the substation close to the track and to connect the 
 negative bus to the rails with short, heavy, cables. In general the 
 negative busbars of substations supplying electrified railw lys are 
 not deliberately earthed, by means of earth plates, connections to 
 piping systems, or otherwise. Two railway electrifications and 
 some of the underground railways in the Metropolitan District 
 provide an insulated fourth rail for return current, leaving the 
 running rails free for signaling. 
 
 7. Negative Boosters. 
 
 Negative boosters are used in many places. In Germany the 
 general practice is not to use them but they are much more ex- 
 tensively used in England (See Table 8) where they are generally 
 found in the larger systems. They are considered more econom- 
 ical than resistances in the return feeders and also better for regu- 
 lation where the load centers shift. In one large .city their use 
 was discontinued after they had been in operation for some time. 
 The Tramways of Danzig, in Germany, operated by a private 
 company and having a maximum load of 600 kw., has used 
 boosters since 1906. 
 
 Boosters are very little used in France, the only system found 
 to be equipped with them was that of the Cie des Tramways de 
 Paris et du Dept. de la Seine. 
 
 TABLE 8 
 USE OF NEGATIVE BOOSTERS, UNITED KINGDOM 
 
 
 Number 
 
 Miles of 
 single track 
 
 Total number of undertakings 
 Number of undertakings using negative boosters. 
 Per cent using negative boosters 
 
 183 
 39 
 
 21.3% 
 
 3,835.0 
 1,152.0 
 30.0% 
 
 Relation Between Booster Capacity and Plant Capacity 
 
 Average, for 25 cases: Booster Capacity 3.9% of plant capacity. 
 
 Highest 9 % for plant of 500 kw. capacity. 
 
 12 % for plant of 800 kw. capacity. 
 
 Lowest 0.8 % for plant of 5,725 kw. capacity. 
 
 0.9 % for plant of 3,500 kw. capacity. 
 
 The use of a negative booster in the return circuit of an electri- 
 fied railway is mentioned in a recent report. The booster was 
 installed for the purpose of relieving load on a section of the line , 
 
EUROPEAN PRACTICE 
 
 149 
 
 a cable being run out from the booster to the section to be relieved. 
 The effects are reported as follows: 
 
 
 Volts drop on Section 
 
 
 Section tested 
 
 
 Per cent Decrease in 
 Drop due to Booster 
 
 
 
 
 Booster on 
 
 Booster off 
 
 
 1st Section 
 
 5.6 
 
 6.75 
 
 17.0 
 
 2d Section 
 
 5.75 
 
 6.9 
 
 16.7 
 
 3d Section 
 
 3.91 
 
 6.12 
 
 36.3 
 
 The booster was not continued in service because it was not 
 effective in relieving the second section. 
 
 8. Double Trolley. 
 
 The double trolley system is not in general use in any of the 
 countries visited. One or two very special cases near Laboratories 
 in Germany, the district within two or three miles, (three to five 
 kilometers) of the Greenwich Observatory, and some conduit 
 tramways of the London County Council System and in Paris 
 were the only cases noted. The double trolley is also used in 
 connection with a few miles of rail less trolley in England. 
 
 9. Three-wire System. 
 
 The three-wire system has been applied to electric railways in 
 a few cases in Germany. In each case the distribution of load 
 between polarities was by districts, that is, certain entire sections 
 have the trolley wire negative. Under these conditions the 
 systems may become considerably unbalanced. 
 
 In France, the Chem de Per Nord-Sud, in Paris, employs a 
 three-wire system with two motors per car, positive and negative, 
 the running rails acting as a grounded neutral while the supply 
 is provided by a third rail and one trolley wire. 
 
 The three-wire system has not been applied to tramways in 
 England. The City and South London Underground Railway 
 employed it, but this was to be discontinued following consolida- 
 tion with other systems. 
 
 10. Negative Trolley. 
 
 The trolley wire was originally made negative in Nuremberg, 
 and in St. Gall, Switzerland. The scheme has been abandoned 
 in both places. This connection has not been used for tramways 
 in Italy, France or England. 
 
150 EUROPEAN PRACTICE 
 
 11. Pilot Wires. 
 
 In Germany permanent means for measuring overall potentials 
 are very generally provided, but the methods of doing this vary 
 widely. Pilot wires are usually provided for new installations in 
 France. 
 
 In England pilot wires are universally used in connection with 
 recording instruments. The practice varies widely, but the most 
 common method employs No. 14 or No. 16 gauge wires laid with 
 the main cables, and extended beyond them. 
 
 12. Bond Testing. 
 
 Bond testing is generally done in Germany on some systematic 
 basis, more often annually, but in some large systems semi- 
 annually. The bond-testing devices are generally of the three 
 contact type with differential galvanometer. Some of these are 
 said to be undesirable on account of the form of the contact, others 
 because the rail points span too short a length, or on account 
 of the type of galvanometer employed, etc. In England it is 
 stated that there is practically no systematic bond testing, except 
 in the large well supervised systems. 
 
 13. Pipes and Pipe Joints. 
 
 Cast-iron pipes in England and Germany are generally of the 
 bell and spigot type with lead calked joints. In Germany flanged 
 joints are frequently used for special fittings, valves, tees and 
 hydrant taps for water mains. Cast-iron pipes are little used in 
 France; pipe joints are either lead calked bell and spigot, or in 
 large pipes flanged, with rubber gaskets. Insulating joints are 
 not used, except that in England it is said that they are occasion- 
 ally used for water pipes in special cases. 
 
 14. Depth of Pipes Below Surface. 
 
 In Germany, 'gas pipes are generally laid 0.8 to 1 meter (2.6 to 
 3.3 feet) and water pipes 1 to 1.5 meters (3.3 to 5 ft.) below the 
 surface. In France, gas pipes are laid where possible 0.6 meter 
 (2.0 feet) below the surface, L. T. cables 0.7 meter (2.3 feet) and 
 H. T. cables 1.3 meters (4.3 feet). In England 1 foot (0.3 meter) 
 is said to be dangerous, 2 feet (0.6 meter) was given as an average 
 by one authority, and 2.5 to 5 feet (0.8 to 1.5 meters) by another. 
 In all cases the above depths are only typical, the practice varies 
 widely. 
 
EUROPEAN PRACTICE 151 
 
 15. Mains on Both Sides of Streets. 
 
 In Germany, France, and England mains are laid on both sides 
 of the principal streets; in Paris, for streets wider than 14 meters 
 (46 feet); also in streets with wood or asphalt pavements, and 
 generally in the larger towns. In narrow streets or unimportant 
 places one main is used. In Paris the pipes for water are located 
 in the sewers, not in direct contact with soil, and remote from 
 trouble. 
 
 16. Insulating Coverings for Pipes. 
 
 In Germany it is held that insulating coverings do not afford 
 protection against electrolysis, as their effect is merely to concen- 
 trate escaping stray currents since perfect coverings cannot be 
 maintained. They should only be used where it is desired to 
 protect against chemical corrosion from the soil. In France, gas 
 engineers stated that insulating coverings were being studied, but 
 it was not believed that they would prove practicable. 
 
 In England insulating coverings are not considered good pro- 
 tection against stray railway currents. High pressure gas pipes 
 have been covered with pitch canvas, and the London Water 
 Board pipes are provided with an asphalt dip coating but more 
 as a protection against chemical corrosion. 
 
 17. Electric Cables. 
 
 Cables are more frequently laid solid in the ground, and con- 
 duits are used less than in America. Metal conduits are only 
 occasionally used in England; where they are used the cable 
 sheaths are bonded to the conduits. Insulating joints are not 
 used in Germany or England for telephone cables. 
 
 D. ELECTROLYSIS CONDITIONS 
 1. General. 
 
 Among the countries visited it was found that in Germany 
 engineers and managers of the utilities concerned were fully alive 
 to the problem of stray current electrolysis, and they were well 
 informed, due largely to the work of their Earth Current Com- 
 mission. In England, although engineers and managers were 
 generally informed, there was little lively interest in the question, 
 due probably to the fact that there does not exist any acute 
 electrolysis problem. 
 
 In France, the Government and the Paris municipality had 
 recently (1914) appointed a Commission to investigate the subject 
 of stray current electrolysis and make recommendations regarding 
 
152 EUROPEAN PRACTICE 
 
 the situation in the City of Paris. In Italy, troubles from electrol- 
 ysis have been considered insignificant. Some of the larger sys- 
 tems in important cities are alive to the situation and are follow- 
 ing with interest the developments in other countries. 
 
 Favorable reports of immunity from electrolysis troubles were 
 based, as in Italy, on the absence of complaints. It was note- 
 worthy that reports of damage were greatest where most thorough 
 investigation had been made. 
 
 2. Voltage and Current Conditions ; Experience with Electrolysis. 
 
 (a) Germany. Considerable damage was found in many cities 
 prior to the application of the Earth Current Regulations ; in one 
 case service pipe trouble occurred as often as once a month. 
 Generally however, extensive damage was not known until it was 
 revealed by investigation. Thus, many of the cities which were 
 surveyed by the Commission, and where more or less corrosion 
 was found, had previously reported no damage. In the past 
 the majority of troubles have been on gas and water pipes, or at 
 least these have received more attention in the reports. No cases 
 of extensive damage to cable sheaths were found. 
 
 Many very thorough tests have been made in Germany and a 
 large majority of these have shown that corrosion was being pro- 
 duced by stray railway currents. In general, the pipe owning 
 interests stated that the situation was such that the work of the 
 Earth Current Commission was urgently needed. Gas and water 
 experts expressed the opinion that the regulations were too lenient, 
 while the railway experts felt that they were too severe, main- 
 taining that a considerable amount of corrosion ascribed to stray 
 railway current, was in fact, due to other sources, or to self- 
 corrosion. 
 
 In general, present conditions in Germany were considered 
 satisfactory where the electric railways have conformed to the 
 Commission Regulations ; or where conditions were already equally 
 good. In other cases the conditions were considered to be un- 
 satisfactory. The more prosperous companies and municipalities 
 spent money for improvements after the publication of the Regula- 
 tions of the Earth Current Commission. Exact information was 
 not available regarding the number of places where changes had 
 been made, but the best information indicated that the number 
 was between 20 and 30. Of these, Danzig, Strasburg and Erfurt 
 expended about 100,000 Marks each, rearranging the resistances 
 of exivSting return conductors, and Dresden was engaged in 1914 
 
EUROPEAN PRACTICE 153 
 
 in insulating the existing bare return conductors. Generally, 
 the most important cities were rapidly improving their return 
 circuit conditions. Also, other undertakings not subject to the 
 Regulations were changing over voluntarily for reasons of policy 
 or economy, or as the result of compromise to avoid litigation; 
 this was said to be the case in 30 or 40 important towns. A 
 litigated case, in Mansfeld, was decided against the gas company 
 on legal grounds as the railway existed before the gas plant. 
 
 Where return circuits have not been remodeled in accordance 
 with the Commission Regulations, overall voltage limits vary 
 greatly, but in the majority of cases they are between 5 and 10 
 volts overall. Measurements were made by the Sub-Committee 
 of one large installation having negative feeders equal in number 
 and area to the positive feeders; it was found that the maximum 
 drops in rails were well within the limits prescribed by the Regu- 
 lations. 
 
 (b) Italy. From a survey made about 1908 in a city of Italy, 
 it was found that the maximum difference of potential in the rails 
 between the station and points about three miles (5 kilometers) 
 distant were as great as 17.5 volts. In this installation they had 
 not received complaints of serious damage by electrolysis, except 
 a few gas service pipes, although the railroad itself had experienced 
 some difficulties on water pipes at* one of its yards. 
 
 (c) France. The Sub-Committee's investigation was some- 
 what limited in France. No adequate or complete tests have 
 been made, although some testing has been done in Paris follow- 
 ing the development of trouble. It is stated that tramways in 
 France generally endeavor to' observe the 1 volt per km. limit 
 (1.6 volts per mile), and that potential differences between pipes 
 and rails rarely exceed one volt. 
 
 In general serious electrolysis troubles were found only in a 
 few places, either created by heavy traffic lines or by peculiar 
 conditions, not readily explainable. Outside of Paris there is 
 little damage caused by tramway systems. In the suburbs of 
 Paris all underground pipe systems are more or less affected. 
 In Paris 60 to 70 cases of damage to pipes have been found in a 
 year the actual cost of repairs was estimated to be 60,000 francs, 
 but it was held that the paramount consideration was the danger 
 to security of service, since nearly all cases caused property losses 
 in buildings, although- there were no explosions. 
 
 At least a third of the total number of cases reported were due 
 to the rearrangement of the old two- wire, three-wire and five- 
 
154 EUROPEAN PRACTICE 
 
 wire systems of electric light distribution, but these troubles 
 were of a temporary character and were promptly remedied as 
 soon as discovered. In the other cases, due to stray railway 
 currents, the troubles were persistent. About twenty litigated 
 cases for electrolysis damage were pending in Paris in 1914. 
 
 A very considerable amount of damage in Paris is due to the 
 "Metropolitan" subway system which claims exemption from the 
 1 volt per km. (1.6 volts per mile) regulation, not being a tram- 
 way. At one place in Paris a potential difference of 6 volts be- 
 tween a railway structure and a pipe was observed by the Sub- 
 Committee. 
 
 There are few telephone cable troubles in Paris due to 
 electrolysis. 
 
 (d) Great Britain. Considerable damage is said to have 
 occurred in the early days of electric traction in England, although 
 such damage was apparently insignificant compared to conditions 
 familiar in America during the same period. Practically no 
 damage has occurred in recent years, and certainly no extensive 
 damage. Two or three cases, local in character and of small 
 extent, have occurred in localities where the Board of Trade 
 Regulations were complied with. 
 
 In England there is very little good evidence in the way of tests, 
 and the general statements of Immunity are based on absence of 
 trouble. The Post Office, and the South Metropolitan Gas 
 Company of London, both make systematic tests and find no 
 trouble except that the Post Office has, from time to time, en- 
 countered difficulties quite local in character, due to stray currents. 
 .The Board of Trade Regulations are not considered onerous by 
 any of the railway engineers consulted. All authorities represent- 
 ing the pipe owning companies, the tramways, the state telegraph 
 and telephone, and the Board of Trade, were unanimous in stating 
 that the electrolysis situation for the properties under their re- 
 spective control was entirely satisfactory. Nevertheless, there is 
 considerable feeling -among the privately owned gas companies 
 that they are not adequately protected, since, as noted elsewhere, 
 they cannot recover damages in case corrosion occurs where 
 Regulations are complied with. 
 
 Overall rail drops for tramways in England are generally very 
 much lower than the Board of Trade requirement, averaging 
 probably 2.5 to 3 volts, with the exception of occasional drops, 
 which may be as high as 15 or 20 volts, due to extraordinary 
 traffic at football matches, etc. The average overall drops for 
 
EUROPEAN PRACTICE 155 
 
 several large cities visited by the Sub-Committee during June and 
 July, 1914, were about 2 volts. Glasgow, which voluntarily 
 adopted a 2 volt rail drop, Manchester, and other large towns, 
 have extraordinarily low rail drops. 
 
 The electrification of branch railway lines has been carried out 
 to a considerable extent since 1914, and some data were obtained 
 in 1920 concerning the voltage drop in the return circuits of such 
 lines. Two electrified sections of an extensive railway system 
 are reported to have maximum instantaneous voltage drops as 
 follows : 
 
 A 43 volts 
 
 B 77 volts 
 
 Another railway reports in general that the voltage drop for its 
 electrified sections is higher than that permitted for tramways; 
 and in particular that the worst section gives a maximum drop 
 of 25 volts for 15 to 20 seconds, with instantaneous maxima 
 considerably higher. 
 
 Potential differences between pipes and tramway rails are said 
 to be generally less than 1 volt. 
 
 E. MISCELLANEOUS OBSERVATIONS 
 
 1. Drainage System. 
 
 Electrical drainage as a palliative measure for electrolysis 
 was formerly applied in one or two cases in Germany, notably in 
 Aachen, but it was abandoned on account of damage produced 
 by it, first due to joint corrosion, and second, damage to other 
 underground structures. It is condemned by the engineers of the 
 Earth Current Commission. 
 
 In England, drainage is not approved as a general measure 
 to afford relief from stray current, although there are a few specia 
 instances of its application to the tramway company's own lead 
 covered cables, where the common practice is to bond to the rails 
 at many points. 
 
 2. Corrosive Effects of Soil; Earth Resistance. 
 
 In Germany the possibility of chemical corrosion (that is, 
 corrosion without an external supply of electricity) is recognized, 
 and distinction is made between such corrosion and that pro- 
 duced by stray currents. Pipe corrosion has actually been found 
 under conditions where it could not have been produced by stray 
 currents. No definite information was obtained in England 
 
156 EUROPEAN PRACTICE 
 
 regarding the corrosive properties of soil, but it was stated that 
 chemical corrosion was known to occur. Such corrosion does not, 
 however, produce acute conditions as in electrolysis; it is r vi ore 
 like ordinary oxidation. 
 
 German reports gave the resistance of soil as varying from 1 
 ohm to 2,000 ohms per cubic meter (1.3 ohms to 2,616 ohms per 
 cubic yard), averaging about 100 ohms per cubic meter, (131 ohms 
 per cubic yard) . In England no specific information was obtained 
 concerning earth resistance. One report states that the provi- 
 sions of clause 5A of Tramway Regulations (for two earth plates 
 not less than 20 yards, (18 meters) apart between which an E.M.F. 
 not more than 4 volts shall produce current of 2 amperes) cannot 
 be met even at permanent water level, and that in general the 
 apparent resistance is about twice that required by Regulations. 
 
 3. Electrolysis Testing Methods. 
 
 In England very little testing is done to investigate electrolysis 
 questions and no technique has been developed for such work. 
 The only extensive work in recent years is that of the Cunliffe 
 brothers, and their work was directed mainly toward the investiga- 
 tion of certain theoretical questions rather than toward the 
 systematic investigation of actual experience with stray currents. 
 
 In .Germany the work of the Earth Current Commission has 
 been already noted. The surveys made by the engineers of the 
 Commission are systematically planned; they are made in the 
 most excellent technical manner. The reports are quite uniform 
 in character; they start with a general investigation of geological 
 conditions, the character of the soil, ground water, etc., continuing 
 with a general survey of the present condition of the railway 
 property, including distribution of load, track and rail resistance, 
 location and loading of supply and return circuit cables and any 
 other electrical data relating to the investigation. The surveys 
 then take up the specific measurements relating to stray current, 
 such as potential differences between pipes and rails, current in 
 pipes, and so forth. Reasoning from the data presented, recom- 
 mendations are made for improving conditions, where improve- 
 ments are needed, sometimes with estimates for the cost of the 
 work. In some cases a supplementary report is made which shows 
 the conditions after the changes have been made. The conclusions 
 arrived at appeared to be practicable and reasonably acceptable 
 to all parties concerned. 
 
EUROPEAN PRACTICE 157 
 
 4. Economic Aspects of the Electrolysis Problem. 
 
 About forty per cent of the electric railway systems in Germany, 
 and about seventy per cent in Great Britain, are municipally 
 owned. In Germany one authority thought that municipalities 
 were more ready than private companies to spend money for the 
 purpose of improving their return circuits, but in England it was 
 thought that there was no difference in this respect. It was said 
 in Germany that where municipalities owned the water, gas, and 
 tramway systems, they may prefer to assume the cost of damage 
 rather than make large expenditure for protecting their pipes. 
 
 Also in Germany, a study of the survey reports of the Earth 
 Current Commission indicated that in no case was the yearly cost 
 of repairs for damage by electrolysis of such amount that, on the 
 surface, large expenditures for improvements would be justified. 
 The Commission, however, while recognizing the importance of 
 the financial aspect of the problem, still recommended the adop- 
 tion of the relatively expensive remedies for the reason they state 
 "that the repairs will certainly become more frequent with lapse 
 of time, and besides the increased expense so caused, there is the 
 liability of service interruption, disturbance of traffic, pavement 
 replacement and even danger of explosion to be considered." 
 
 Opinions differed in Germany as to whether or not the prevailing 
 regulations constituted a financial hardship. In England, the 
 Board of Trade Regulations are nowhere considered a hardship, 
 and where inquiry was made as to whether the existing regulations 
 had retarded the development of electric railways, the authorities 
 consulted uniformly stated that this was not the case. It appears 
 that in fact a saturation point has been reached, and busses are 
 being used where tramways would not pay. Traffic conditions 
 are said to be quite as heavy in England as in the United States. 
 Only one authority in England ventured an estimate of the aver- 
 age load factor for English electric railways systems; he estimated 
 it to be thirty-five per cent. 
 
 5. Application to American Conditions. 
 
 Disputes on account of electrolysis troubles have been prevalent 
 in the past in all countries having any considerable electric railway 
 development, before systematic cooperative studies or regulations 
 were applied; this in spite of the fact that the mode of life and 
 distribution of population and industries are more favorable than 
 in American cities. The average weight of cars in foreign cities 
 is less than in America, and the tramway traffic and power re- 
 
158 EUROPEAN PRACTICE 
 
 quirements may be one-fifth or less in Europe than in America 
 for cities of the same population. 
 
 A city like Berlin with over 2,000,000 inhabitants handled all 
 of its transportation with a maximum load of about 30,000 kw. 
 (Chicago with over 2,200,000 population required a maximum load 
 of about 200,000 kw.) Manchester with a population of 1,250,000 
 and Glasgow with 1,000,000 had traction loads of 11,000 kw. and 
 11,500 kw. respectively. (Boston and the territory served by its 
 traction system with about 1,150,000 people, required station 
 capacity of 75,000 kw.) Milan with a population of over 600,000 
 had a traction load of approximately 8,000 kw., and Nurnberg 
 with 350,000 inhabitants used only 1,000 kw. (The city of 
 Worcester, Mass., with a population of approximately 160,000 
 required power station capacity of 7500 kw.). These comparisons 
 should be taken into consideration in applying to this country the 
 results of this investigation of foreign practice. 
 
 These comparisons, however, should not be taken as a definite 
 index to comparative electrolysis conditions, since many other 
 factors are involved. Regardless of the degree of improvement 
 which economical limitations may make permissible to accomplish 
 in local situations, the fundamentals for the solution of the elec- 
 trolysis problem evolved abroad merit the most careful study to 
 ascertain their possible application to American conditions. 
 
 F. SUMMARY 
 
 In Europe, the effectiveness of the cooperative or regulatory 
 measures applied to the electrolysis problem may be summarized 
 as follows : 
 
 Germany, through voluntary cooperation, has probably remedied 
 the former dangerous electrolysis conditions for all of its important 
 systems. The instrumentality of agreements on definite technical 
 standards was sought in preference to legislation. 
 
 France has not been as successful in bringing prompt results 
 through legislation as has Germany through technical cooperation. 
 
 England which has had government regulation for many years 
 has now no electrolysis troubles or disputes. 
 
 Italy will probably give more consideration to the subject of 
 electrolysis whenever the general conditions will permit. 
 
 The methods followed to attain the satisfactory results obtained 
 abroad are these : 
 
 1. Maintenance of good bonding. 
 
EUROPEAN PRACTICE 159 
 
 2. Elimination of intentional contacts, and liberal separa- 
 tion wherever possible, of pipes and rails. 
 
 3. Avoidance of bare copper returns and use of insulated 
 returns in all installations where the conductivity of the rail 
 alone would give a too great maximum drop. 
 
 4. Use of insulated return feeders with balancing resist- 
 ances, or to a lesser extent ''boosters" for the purpose of 
 maintaining equality of rail potential at the feeding points 
 of all reeders. 
 
 Small feeder drops and frequent substations to give close 
 line regulation. 
 
 G. EUROPEAN REGULATIONS ADOPTED AND PROPOSED 
 
 GERMANY EARTH CURRENT COMMISSION'S RECOMMENDATIONS 
 
 RECOMMENDATIONS OF THE GERMAN EARTH CURRENT COMMISSION AS 
 ADOPTED BY THE GAS, WATER, AND RAILWAY INTERESTS OF GERMANY. 
 
 Regulations for the protection of gas and water mains from 
 the electrolytic action of currents from direct current electric 
 railways which use the rails as a return. 
 
 Accepted for two years at the yearly meeting of 1910 and 
 for a further two years at the yearly meeting of 1912. 
 
 Published in the Electrotechnische Zeitschrift, 1910, page 
 491, and 1911, page 511. 
 
 Section 1. Application of Rules. 
 
 The following rules govern the installation of direct current 
 railways or sections of direct current railways which use the rails 
 for carrying the return current. Unless otherwise mentioned the 
 herein given admissible potential values should be adhered to 
 when laying out new railways. For determining the resistance 
 of a line, the rails only must be taken into account as current 
 carrying mediums and the assumed resistance of the rails, as well 
 as the assumed percentage increase of resistance due to the bonding 
 must be stated. 
 
 These values must not be exceeded, either when making the 
 necessary calculations or by the plant when in actual normal 
 operation. 
 
 These rules do not apply when railways are laid with special 
 track or when the rails are laid on wooden sleepers, in which case 
 there is generally an air clearance between the rails and the stone 
 ballast; but the rules do apply if this air clearance does not exist, 
 as at grade crossings, unless an equivalent insulation is provided 
 
160 EUROPEAN PRACTICE 
 
 for locally. Further, these rules do not apply to railway lines 
 which do not approach closer than 200 meters to an underground 
 pipe network. 
 
 Explanation* 
 
 The regulations apply only to direct current railroads or sec- 
 tions of such, using the rails as conductors. Railroads not using 
 the rails as conductors are eliminated from the start, because the 
 same do not send any currents into the earth and therefore cannot 
 have any damaging influence on the pipes. According to the 
 experience reached so far, alternating current seems to have very 
 little effect, so that any extension of these rules to cover also 
 alternating current railways does not seem justified. At any 
 rate, the conditions produced by alternating current railways are 
 not yet sufficiently understood to allow of establishing any restric- 
 tions in regard to their equipment and operation for the protection 
 of pipes. 
 
 In case a railroad is operated partly with direct current and 
 partly with alternating current, these regulations apply only to 
 those sections, the rails of which carry direct current. The fixed 
 upper limits of permissible potentials apply to the design of the 
 plant, unless otherwise stated, and in the calculations only the 
 rails and the bonds are to be considered as far as the conductivity 
 and the resistances of the conductors are concerned. The assumed 
 resistance of the rails and the increase of same by the resistance 
 of the bonds is to be stated, and such limiting values are not to be 
 exceeded either by calculations or in practice. 
 
 The earth as a shunt is not considered. Through contact of 
 the rail network with the ground, a part of the current passes 
 into the ground and the potentials of the rail network are thereby 
 lowered as compared with a case of perfect insulation from the 
 ground, the effect becoming greater, the more the current passes 
 into the ground. It is, therefore, not correct to take the differ- 
 ences of potentials ' as found immediately after the construction 
 of a rail network as a basis for estimating the safety against 
 damaging influences, but it is necessary to go back to the first 
 cause, that is to say, the differences of potential as they would be 
 if the rails were completely insulated. 
 
 This rule allows of an exact calculation of the conditions during 
 
 *NOTE: This explanation and the other following are included in the 
 German Earth Current Commission's recommendations. 
 
EUROPEAN PRACTICE 161 
 
 the design of the plant without any uncertain and varying values 
 for different localities. The limit values are not to be exceeded 
 either during the calculations or at the actual practical test. 
 The method of the practical test will be discussed in Section 3. 
 The projection of the plant is, therefore, to be based on assump- 
 tions as correct as possible with regard to the resistance of the 
 rail, the cables, and the consumption of current, and it is advis- 
 able to consider also a later increase of the traffic. 
 
 Railroads, the rails of which are insulated on special roadbeds, 
 generally have such a great resistance against the earth that 
 passage of current into the ground of such magnitude as to be con- 
 sidered dangerous to pipes does not occur. Higher potentials, 
 therefore, are permissible for such railroads, assuming that a 
 sufficient insulation is provided for also on grade crossing, etc. 
 
 As a means to this end are to be considered : 
 
 Insulating strata between rails and ground, for instance, tar 
 paper, which must extend on. all sides sufficiently beyond the 
 place in question; or the surrounding of the pipes with insulating 
 material. Such places are to be inspected from time to time to 
 ascertain the effect of such insulation. 
 
 For the exemption from these regulations the laying of the rails 
 on a special roadbed is required, because it is only in this way that 
 a permanent insulation can be reached and maintained. About 
 the details of the system of insulation to be used, no rules were 
 issued. A lasting insulation is to be guaranteed by the way in 
 which the rails are laid. The laying of rails on wooden ties as 
 mentioned above is intended as an example only. At any rate to 
 secure satisfactory insulation it is imperative that the rails be 
 nowhere in contact with the moisture of the ground, as this 
 greatly favors the passage of the current into the ground. 
 
 Tracks which are at all points at least 200 m. distant from any 
 pipes are exempt, because any current coming over such an 
 extended area spreads to such a degree that its density cannot 
 possibly be harmful. In this respect concession has been made 
 to long outlying railway lines because the subjection of such to 
 these regulations would entail great economic disadvantages in 
 certain cases. The maintenance of good conductivity on such 
 outlying sections is to be strongly recommended so as to prevent 
 the return currents from reaching a dangerous density where 
 such sections join the rails of an inner rail network, i.e., a density 
 exceeding the limit given in Section 5. 
 
162 EUROPEAN PRACTICE 
 
 Section 2. Rail Conductors 
 
 All rails serving as return conductors should be built with regard 
 to this requirement, should be made as good conductors as possible, 
 and should always be kept in good order. 
 
 The percentage of increase of the resistance of a given length 
 of track due to the bonding should not exceed the value assumed 
 when laying out the railway, and must not be more than 20% 
 more than the resistance of the same length of track if the rails 
 were without joints and of the same cross-section and the same 
 specific conductivity. On laying out a railway line consisting of 
 main and auxiliary rails, the combined cross-section of both rails 
 can only be taken into account when determining the resistance 
 of the track, provided the auxiliary as well as the main rails are 
 properly bonded and cross bonded. 
 
 At rail crossings and at switches, the rails must be well bonded 
 by special bridge bonds. 
 
 On single tracks as well as on lines where several tracks are 
 lying side by side the rails must be efficiently cross bonded and 
 these cross- and bridge-bonds must have a conductivity at least 
 equal to a copper conductor of 80 square millimeters. 
 
 At all movable bridges or similar structures which necessitate 
 an interruption of the rails, special insulated conductors have to 
 be provided which secure a continuous connection between the two 
 rail ends. In such cases, the voltage drop at average load must 
 not exceed 5 millivolts for each meter distance between the inter- 
 rupted rails. 
 
 All current carrying conductors which are connected to the 
 rails, must be insulated from earth, excepting short connections 
 such as bonds, cross-bonds and bridge-bonds at switches and 
 turntables. If such bonds are laid not deeper than 25 centimeters 
 into the earth, they may be bare conductors. 
 
 Explanation 
 
 The first condition for the reduction of stray currents and for 
 the effectiveness of all the proposed precautionary measures, is 
 the good conductivity of the tracks and the maintenance of this 
 conductivity. High resistances of the single sections cause an 
 increase of the current passing into the ground. The maintenance 
 of the good conductivity of the rails also is to the economic interest 
 of the railroad, because a bad conductivity will, under certain 
 circumstances, cause loss of energy. 
 
 It is not desirable to issue rules concerning the cross-sections 
 
EUROPEAN PRACTICE 163 
 
 of rails or for the conductivity of the steel because the cross-sec- 
 tion and the chemical composition of the steel are both determined 
 by mechanical considerations; the conductivity is dependent on 
 the composition of the steel, while the conductance of the rail 
 depends on both the conductivity and the profile. 
 
 The resistance of a rail network is widely influenced by the 
 quality of the electrical connections of the rails at their joints. 
 
 The rules do not recommend one or another system of connec- 
 tions at the joints, but give data covering the permissible increase 
 of the resistance by such connections. 
 
 In consideration of the varying resistance of rails of different 
 profile, it is not possible to establish a uniform permissible resist- 
 ance for a bond but the permissible increase of the total resistance 
 of a section by all the bonds is given. This increase must not be 
 over 20 per cent. Inside of these limits the designing engineer 
 may assume any increase of the resistance by the bond, but it 
 must be considered that the increase assumed must be perma- 
 nently maintained later on (compare Sections 6 and 3) . 
 
 It will be well to assume during the design of the plant, the in- 
 crease of resistance of the bonds as very near the permissible limit. 
 This is very important when shorter rails are to be used, with the 
 consequent greater number of joints, the maintenance of which is 
 correspondingly more difficult and, therefore, an increase of 
 resistance through deficient bonds to be expected. The conduc- 
 tivity of rails is to be ascertained on a number of samples before 
 the rails are laid, so as to have a guarantee that the calculated 
 resistance will correspond to the resistance of the finished work. 
 
 The measurement of the resistance is made, by measuring the 
 current and the potential on a raitas long as possible and insulated 
 from its supports ; the potential terminals should include a part of 
 the circuit between the current contacts and they should be at 
 least 0.5 meter distant from these current contacts. A simple 
 calculation gives the conductivity of the rail by using the value 
 shown by ammeter and voltmeter. The conductivity of the rails 
 now in use is generally found to be between 4 and 5.5 Siemens 
 (10.5 to 14.4 times the resistivity of copper). 
 
 In cases where main and auxiliary rails are to be used and where 
 the combined cross-section of both is taken into calculation, the 
 conductivity of the auxiliary rail also is to be measured as the 
 same may differ considerably from the conductivity of the main 
 rail. 
 
 At crossings and switches a loosening of the rail connections 
 
164 EUROPEAN PRACTICE 
 
 will take place caused by the vibrations brought about by the 
 passage of the rolling stock, for which reason such places are to be 
 bridged specially by electrical conductors. The cross connections 
 serve the purpose of eliminating differences of potentials between 
 tracks running side by side and also to insure a good metallic 
 connection between the rails on one side of a track in the case of a 
 temporary low conductivity of single joints or interruptions. 
 
 It seems advisable in consideration of the different length of 
 rails, not to give an absolute distance between the cross connec- 
 tions, but to establish their number by the number of joints. 
 The bonds and cross-connections may be of any material as long 
 as their conductivity reaches at least that of a copper connector 
 of 80 square mm. For the connection of interrupted tracks, as 
 for instance at movable bridges, insulated cables are required 
 because of the presence of water or other substances in the soil, 
 which highly favor the passage of currents into the ground. The 
 highest permissible drop in potential at average load has been 
 fixed at 5 millivolts per meter distance between the places of 
 interruption, to insure a small difference of potential between 
 these points. 
 
 Furthermore care is to be taken that the tracks in a movable 
 bridge are in good contact with the tracks on both sides of it. 
 The following is an example of the calculation of a cable bridging 
 across the gap. 
 
 When the distance between the tracks at the point of interrup- 
 tion equals 30 meters, the permissible difference of potential, 
 therefore, is 5 x 30 which equals 150 millivolts. The current to 
 be carried across is assumed to be 120 amperes and the length of 
 cable 30 meters. Assuming a specific resistance of 17.5 milliohms 
 per meter and square millimeter, the resulting cross-section is: 
 
 17.SXL/ 17.5X30X120 
 
 q - =- = 420 sq. mm. 
 
 1 O\J 
 
 Inasmuch as the increase of the surface contact between the 
 conductors and ground results in an increase of the current pass- 
 ing from the conductors into the ground, the conductors connected 
 to the rails, especially those lying deep enough to come into 
 contact with the moisture of the ground, are to be insulated 
 conductors. Only short connections, such as jumpers on cross- 
 ings and switches, are exempt from this rule on account of the same 
 not lying deeper than 25 cm. under the surface, which means that 
 they hardly come into contact with the moisture of the ground. 
 
EUROPEAN PRACTICE 165 
 
 The increase of surface of the contacts with the ground by these 
 conductors is too small in proportion to the total surface of the 
 rail network to cause any apprehension regarding the currents 
 passing into the ground. 
 
 Section 3. Rail Potential 
 
 A railway network is divided into two sections, first, the open 
 road connecting the various townships, and second, the urban 
 network. 
 
 In the urban network and for a distance of 2 km. beyond, the 
 voltage drop between any two rail points should never exceed 
 2.5 volts when the line is working under normal conditions, and 
 the drop in the rails for each kilometer of open road should not 
 exceed 1 volt. Occasional night cars are not to be considered in 
 determining the average load. 
 
 In townships through which only a single line is run, without 
 local rail network, the total voltage drop in the rails must not 
 exceed 2.5 volts from end to end of the township's pipe network. 
 
 Any apparatus which is supplied with current and which is 
 connected to the railway network must not increase the voltage 
 drop above the stated limits. 
 
 If various railway systems are connected together either through 
 the medium of the rails or through the power station, each system 
 must fulfill the above conditions. A rail system in a township 
 with an independent pipe network has to comply with the above 
 regulations also. 
 
 Exceptions from these rules in regard to the voltage drop in a 
 railway network are admissible if local conditions and service 
 necessitate and justify such exceptions. If, for instance, the 
 service as is the .case in freight yards covers only a small por- 
 tion of the day, the above limits of rail drops may be exceeded. 
 In yards with a service up to three hours daily, double the above 
 values are permitted, and with a service up to one hour, four times 
 the above values are allowed. 
 
 Explanation 
 
 As mentioned in Section 1, the rail network is to be considered 
 as insulated from the ground, so that the earth as a shunt is not 
 considered. 
 
 The resistances of the single sections are to be calculated from 
 the resistance of the rails under observance of the rules in Sections 
 1 and 2. 
 
166 EUROPEAN PRACTICE 
 
 For the calculation of the potentials the value of the average 
 current is to be used, as the magnitude of electrolytic decomposition 
 of the pipe metal depends on the quantity of current, that is to 
 say, the product of current and time. The highest values have 
 not to be considered for the calculations. To find the consump- 
 tion of current the average service as per schedule has to serve 
 as the base. 
 
 The average current consumed on single sections can be cal- 
 culated from the number of car km. or ton km. to be covered, by 
 using the value for the consumption of current which, according 
 to experience, and in consideration of the local conditions, is used 
 for one car km. or ton km. 
 
 But it is also permissible to distribute the consumption of 
 current over the whole net in a way corresponding to the locations 
 of the single trains at the time of the average load and to calculate 
 for each train the consumption of current taking into considera- 
 tion the weight of the cars, the speed and operating conditions 
 (grade, stops). 
 
 In regard to the schedule, the difference between summer and 
 winter service is to be considered. The increase at regular inter- 
 vals, as for instance on Sundays, is to be taken into account. 
 Small deviations from the schedule, as for instance, single night 
 cars, or auxiliary cars, shall not be considered, because the first 
 would reduce the average value out of proportion, and the fre- 
 quency of the second cannot be estimated at the time of the calcu- 
 lations and otherwise are not of any appreciable influence on the 
 final results. 
 
 It is impossible to get regulations embracing all conditions 
 and possibilities land it is therefore necessary to consider all 
 peculiarities of a plant during its projection.. If there are any 
 additional places connected to the rails, where current is used for 
 stationary motors, station lighting, etc., these are to be considered. 
 
 After the drops in potential on the central sections have been 
 tabulated, based on the above calculations, the distribution of the 
 potential in the rail network can be found. In addition to the 
 foregoing data for the calculation of the drop in potential on the 
 single sections, consideration is to be given to the proposed return 
 cables and, in case of a three wire system, to the direction of 
 the current in the districts of different polarity. 
 
 Difference in potential between any two points of the rail net- 
 work must answer the following conditions : 
 
 Around every individual pipe network (meaning a network not 
 
EUROPEAN PRACTICE 167 
 
 in metallic contact with any other network) and also around single 
 pipes, a zone of 200 m. is to be circumscribed and all tracks 
 lying outside of this zone are not be to considered in connection 
 with these regulations, as per last part of Section 1 . 
 
 For each of the rail branches lying inside of these individual 
 pipe networks, the following rules apply : 
 
 If there are any branches of the railroad inside of a pipe net- 
 work, including the 200 m. zones, a belt 2 km. wide is to be laid 
 around the inner rail network. Inside this belt the potential of 
 the rails between any different points must nowhere exceed 2.5 
 v., as long as no portion of the rails is more than 200 m. distant 
 from the nearest pipe along its total length. (Compare Fig. 32). 
 
 On the sections outside the 2.5 v. districts, the drop in potential 
 must not exceed 1 v. per km. This applies to outlying sections 
 which are shown in Fig. 32 by heavy dotted lines. 
 
 In the case of a railroad with no branches (country roads) and a 
 pipe network, the drop in potential inside the pipe network must 
 not exceed 2.5 v. (Compare Fig. 33). The rule establishing a 
 drop of 1 v. per km. states that the current in the track must not 
 
 exceed === if W is the resistance of the track in ohms per km. For 
 a uniform load of a section of L km. length and a uniform resistance, 
 the permissible drop in potential is -^ v. i.e. one-half the drop in 
 
 one rail. The calculation of this drop is also is based on the 
 average load, according to the shedule. 
 
 Strict rules have been issued for the interior rail network with 
 its many branches, as it mostly covers the same area as the pipe 
 network. This has been done in consideration of the greater 
 surface of contact between ground and rails and pipes, respectively, 
 which increases the probability of a passage of current through 
 the ground. The potential of 2.5 volts for this district has been 
 judged permissible because, according to the results of previous 
 investigations, it is to be assumed that this potential will not 
 under ordinary conditions cause any danger to pipe lines beyond 
 practical limits. To avoid as much as possible any greater con- 
 centrations of ground and pipe currents at the outlying sections 
 which immediately join the inner rail network, and where im- 
 portant parts of the pipe network often extend, strict rules have 
 been issued covering the district inside the 2 km. belt around the 
 inner rail network. 
 
 For the outlying section an economical advantage has been 
 
168 
 
 EUROPEAN PRACTICE 
 
 contemplated by limiting the drop in potential to 1 v. per km. 
 Railroads interconnected by their rail networks or by a common 
 power plant are to be considered as one system because such rail- 
 
 District of interior pipe network. 
 District of 200 m. around pipes with no branches. 
 Railroads in the 25 V. District. 
 Railroads in the I V-Km District. 
 Railroads wth no Restrictions. 
 Fig. 32. 
 
 District of the pipe -network with the 200m: belt 
 surrounding it and the pipes with no branches.; 
 District of the interior Rail-network with JjleKni., 
 belt surrounding it 
 
 Railroads m the 2/5 V. District (shaded by both 
 
 horizontal and vertical lines). 
 
 Railroads in the IV-Km District (shaded by 
 horizontal lines) 
 
 Railroads with no restrictions (not shaded, or by 
 
 vertical lines only> 
 
 KEY TO CALCULATION OP VOLTAGE DROP IN RAILS 
 Fig. 33. 
 
 roads influence each other, inasmuch as equalizing currents will 
 flow between their rail networks. 
 
 Deviations in both directions from these potentials can be 
 justified by certain circumstances in case of especially good 
 
EUROPEAN PRACTICE 169 
 
 conditions of the ground, that is to say, in very dry dirt an increase 
 of the potentials may be permissible. But even in such cases it is 
 advisable to be cautious in allowing such an increase, so as not to 
 violate the rules as given in paragraph 5. Where the conditions 
 are unfavorable, for instance, where moist ground of especially 
 high conductivity prevails, it is advisable, to remain below the 
 limits. For railroads with brief daily operation concessions have 
 been made because damage to the pipes depends upon the dura- 
 tion of the influence of the current so that, considering the short 
 time of operation, even greater currents cannot cause any appreci- 
 able damage to the pipes. 
 
 For railroads of three hours daily operation double drop in 
 potential is allowed, while for railroads of one hour operation, 
 four times the drop is permissible. Wherever the rail network 
 is not sufficient to carry the current without exceeding the per- 
 missible potential in the network, the whole plan for the return 
 of the current must be altered, and improvement will be reached 
 by providing return cables in which, if necessary, resistances or 
 boosters may be inserted. The resistances should be variable so 
 as to correspond with the variable conditions of service and opera- 
 tion. In cases where the railroad system is fed from several 
 power plants a reduction of the drop in potential in the rails may 
 be brought about by shifting the loads of the several power plants. 
 
 The arrangement of the cables and resistances can be made in 
 so many different ways as to make a general rule for all cases 
 impossible. It is recommended to investigate thoroughly the 
 cases under observation, because considerable saving in the con- 
 struction and operation of the plant may be achieved by a careful 
 layout. 
 
 The keeping of the return points at the same potential is recom- 
 mended as a precautionary measure but not required. The same 
 offers a certain guarantee of the possibility of keeping the differ- 
 ence of potential within the 2.5 v. limits. 
 
 Furthermore, the use of the three- wire system with the rails 
 as a neutral conductor is worthy of consideration. In this system 
 the difference of potential in the rails depends on the distribution 
 of the positive and negative feeder districts. This distribution 
 again depends on the local conditions of the plant, so that no 
 general rules can be given in regard to it. 
 
 Alterations of the conditions of operation can be counteracted 
 by switching the load to the positive or negative side of the 
 system. The rules do not recommend any certain system, but 
 
170 EUROPEAN PRACTICE 
 
 leave it entirely to the projecting engineer to select the one best 
 adapted to existing conditions. The damage to pipes takes place 
 mostly at points of low potential on two-wire railroads, in the 
 neighborhood of the return points ; and on three- wire railroads, in 
 the districts of negative feeders; because it is mainly here that 
 the current leaves the pipes. It is advisable to place the return 
 points of the negative feeder districts whenever possible in loca- 
 tions with dry ground of low conductivity and as far as possible 
 from such pipe lines as are of importance for. the water and gas 
 supply. 
 
 The permissible limits of differences in potential in rails must 
 not exceed, either according to calculations or at the practical 
 trial, the limits given in Section 1, of these rules. The measure- 
 ment of the difference in potential is made by means of test 
 wires as called for in Section 6. The measurements of differences 
 in potential are limited to those points which, according to calcu- 
 lations, come nearest to the established limits. Wherever long 
 lines, as, for instance, telephone wires, are available, it is advisable 
 to use them for these measurements otherwise several test wires 
 may be connected in series or temporary test lines may be in- 
 stalled. Finally, the restilts of single measurements may be 
 computed to reach the same final results. Only high resistance 
 voltmeters should be used for these measurements so as to make 
 the resistances of the test wire and .contacts negligible. The 
 pointers of these instruments should have the slowest movements 
 and a good damper arrangement, so as to give good readings even 
 under strong fluctuations. For all measurements only average 
 values are considered. All measurements are to be extended 
 over a full period of operation which results from the average 
 frequency of trains. 
 
 Section 4. Resistance Between Rail and Earth 
 
 The resistance between ground and the rail which is used for 
 carrying the return current should be kept as high as possible. 
 When the conditions of the ground or the situation of the track 
 are not favorable for this purpose, the resistance should be in- 
 creased by a special effective insulation. 
 
 The rails or any conductor connected to the rails must not be 
 in contact with the pipes or any kind of metal buried in the 
 ground. Furthermore, care must be taken that the distance 
 between the nearest rail and any metallic part of the pipe lines 
 or connections to them which project above the ground or lie 
 
EUROPEAN PRACTICE 171 
 
 near the surface, be kept as great as possible, and should never 
 be less than one meter. 
 
 Stationary motors, lighting installations or any other plant 
 which receives current from a railway system which uses the rails 
 for carrying the return current, must be connected to the rail 
 network by means of insulated conductors. Excepted are short 
 connections of not more than 16 square millimeters which are not 
 deeper than 25 centimeters in the ground and which are at a dis- 
 tance of at least 1 meter from any part of a pipe network. These 
 connections may be of bare metal. In order to increase the resist- 
 ance between rail and ground it is recommended to use a bedding 
 of high resistance and to provide good drainage, also to render 
 the bedding water-tight to the roadbed for a sufficient width on 
 both sides of the rail. 
 
 The use of salt for the melting of snow and ice, should be limited 
 to cases of absolute necessity. 
 
 Wherever sufficient distance between the rail and such parts of 
 the pipe line as project above the surface is not obtainable, it is 
 advisable to change the pipe run, or where this is not possible, to 
 use insulating strata (such as vitrified clay, masonry or wooden 
 conduits, etc. 
 
 Explanation 
 
 The magnitude of currents passing into the ground depends 
 not only on the potentials in the rail network, but also on the 
 resistances between the rails and the pipes and on the resistances 
 of the pipe lines themselves. It will always be of advantage to 
 increase the resistance of the ground between the rails and the 
 pipes. An artificial increase of the resistances of the pipe line 
 can 'be achieved for instance, by the use of insulating flanges, 
 couplings, etc. Aside from the technical difficulties of installing 
 such insulating parts into gas pipes, and especially water pipes 
 with a high pressure, and of insuring their lasting tightness, it 
 would be difficult to provide these insulating pieces in the necessary 
 numbers and to take care of their correct distribution. A wrong 
 arrangement of the same will lead to an extraordinary concentra- 
 tion of currents at these insulations with consequent corrosion in 
 these places. A greater part of the drop in potential between 
 pipe and rail originally takes place in the roadbed as can be easily 
 understood and it is therefore required to render this resistance 
 as high as possible by the good insulation of the roadbed, good 
 drainage, etc., and to maintain it thus. 
 
172 EUROPEAN PRACTICE 
 
 In the same measure that the increase of the resistances between 
 rail and pipe is recommended, the use of any means to reduce these 
 resistances, is to be warned against. Such means to be considered 
 are ground plates, connections of metals in the ground, and espe- 
 cially metallic connections between the rails and the pipes. The 
 last will reduce the density of the current at the point of connec- 
 tion to the pipe, but they cause an increase of the pipe current and 
 of the ground currents in general which may cause damage in 
 other places, as, for instance, at interruptions in the pipe line or 
 at crossings with other lines. Any local measure taken must be 
 considered with regard to its effect on the pipes in other localities. 
 
 Metallic connections between different pipe networks also are 
 to be judged from this viewpoint. Immediate contact of any 
 parts of the pipe lines with the rails, or too close an approach, has 
 the same effect as direct metallic connections and is, therefore, to 
 be avoided. (By a relocation of rails or pipes or installation of 
 insulating strata). 
 
 Especially in cases of stationary motors or lighting plants 
 connected to the railroad system, there exists on the premises 
 danger of an accidental or deliberate connection or contact with 
 the pipe lines. It is, therefore, necessary to have strict rules 
 regarding the return cables from such plants. 
 
 Section 5. Current Density 
 
 The above rules are intended to prevent the destruction of the 
 pipes by electrolysis. The rate of destruction is in direct propor- 
 tion to the amount of current leaving the pipe. 
 
 Any pipe line where the current leaving the pipe exceeds an 
 average density of 0.75 milliampere per square decimeter and 
 where this current is due to a railway, may be considered en- 
 dangered by this railway, and further preventive measures must 
 be taken. 
 
 For railways with freight service when the service is of com- 
 paratively short duration, exceptions as already mentioned are 
 permissible. 
 
 In cases where the current leaving or passing into the pipes 
 changes its direction, the current passing into the pipe must be 
 taken as nil when determining the average density, until further 
 experience has been gained in this matter. 
 
 Explanation 
 
 Inasmuch as a total elimination of all damages to pipes would 
 be in most cases possible only at a disproportionately high cost, 
 
EUROPEAN PRACTICE 173 
 
 which would far exceed the cost of any possible damage to the 
 pipes, it is necessary to allow a certain limited damage, that is to 
 say, a damage which is of little practical importance and which 
 does not noticeably shorten the life of the pipes. These rules 
 have therefore been compiled on the basis of the average conditions, 
 that is to say, such as are mostly met with, and it is to be expected 
 according to previous experience that the damage done to pipe 
 lines by the stray currents from electrical railways generally will 
 remain limited to the practical allowable limit wherever these rules 
 are observed. Under exceptionally bad conditions, that is to say, 
 under conditions which very much favor the origin of stray cur- 
 rents, greater corrosion of pipes in certain places can hardly be 
 avoided, even if the limits of the drop in the potential in the rails, 
 as laid down in Section 3, are not exceeded. It is, therefore 
 advisable to establish some measure for the elimination of imme- 
 diate danger to the pipes. 
 
 For the judgment of the damage attributed to a railroad system 
 the density of the current leaving the pipes and returning to the 
 railroad system is indicative. 
 
 The density of the current at the pipe can be measured only 
 after the completion of the plant. These measurements must be 
 made during the time of operation,. as per schedule, and as de- 
 scribed in Section 3. The average density is important and is 
 obtained from the computation of the results of several measure- 
 ments, each of which follows a whole period of service. 
 
 Measurements of current density can be made, for instance, 
 by means of a milliammeter and non-polarizable frame as designed 
 by Prof. Haber. This frame contains two copper plates which are 
 insulated from each other and which for the prevention of polariza- 
 tion are covered with a paste of copper sulphate and 20 per cent 
 sulphuric acid, over which a parchment, soaked with sodium sul- 
 phate is laid. The frame is filled with dirt except between the 
 plates, and placed alongside the pipe at right angles to the as- 
 sumed direction of the current and then covered with dirt. A 
 very sensitive ammeter connected to the copper plates will indi- 
 cate the current passing through the frame and the density of 
 this current can readily be calculated by taking into account the 
 surface of the copper plates inside the frame. Inasmuch as here 
 also only average readings are to be considered, it is advisable to 
 use an instrument with very slow period. 
 
 According to investigations made so far, absolute danger to the 
 pipes results whenever the density of the currents leaving the 
 
174 EUROPEAN PRACTICE 
 
 pipes reaches the average value of 0.75 milliampere per square 
 decimeter. For railroads with small periods of operation an excess 
 up to double and quadruple, respectively, the above value is 
 permissible according to the rules laid down in Section 3. 
 
 Wherever the direction of the current changes, the current 
 entering the pipes are not to be considered in the calculations 
 of the average density, inasmuch as it is not yet established that 
 such currents will add to the metal of the pipes. Wherever the 
 average values are exceeded, special precautionary measures 
 are to be taken, the nature of which can be determined only by 
 the local conditions. In many cases it is sufficient to protect a 
 very limited section of the rail network, to which end the further 
 reduction of the drop in the rails may not be necessary, but which 
 may be attained by other means as, for instance, the re-location 
 of short sections of tracks or pipes, or the artificial increase of the' 
 resistances between rails and pipes at such points. 
 
 In all cases the question arises whether the railroad is to be 
 considered as the only cause of current concentration, as other 
 causes may be found to be responsible for a part of the current 
 on the pipes; for instance, bare neutrals or poor insulation in 
 other electrical systems, the natural electrical elements resulting 
 from the use of different metals in the pipe lines, or from different 
 chemicals in solution in the ground. That part of the current 
 which is attributable to the influence of the railroad can be deter- 
 mined by comparison with the measurements of the current 
 during the period of no operation. In many cases the influence 
 of the railroad can be judged from contemporaneous measurements 
 of current density and the potential between pipe and rail. Under 
 certain circumstances it is possible to find the degree of influence 
 of the railroad and of other electrical plants operating at the 
 same time, by establishing the course of the current in the ground. 
 For this investigation electrodes that cannot be polarized are used 
 as contacts from the test line to the ground. The measurements 
 should preferably be made by the potentiometer method in order 
 to eliminate drop at the electrodes due to the current flow, but 
 this method is difficult in practice on account of the rapid fluctua- 
 tions of the voltage. It will be sufficient in most cases to make 
 the measurements with a voltmeter of very high resistance so that 
 the current passing through the electrodes will be very small. 
 It should be emphasized that such measurements should be made 
 by experts only, as deviations from the right method which seem 
 of no importance often give useless results. 
 
EUROPEAN PRACTICE 175 
 
 Section 6. Control. 
 
 In order to be able to test the potential at the return points of 
 the rail system of a given territory, pilot wires are to be connected 
 to these points and carried to a central testing place. 
 
 Before a service may be increased the potential distribution in 
 the rail network must be retested. 
 
 The rail bonds and bridge connections are to be retested once 
 yearly by means of a suitable rail joint tester and must be ar- 
 ranged so that they fulfill the rules of Sections 1 and 2. Con- 
 nections, the resistance of which has been found greater than that 
 of an uninterrupted rail of ten meters length, must be repaired 
 to comply with these rules. 
 
 Explanation. 
 
 The control of the drop in potential in the whole network would 
 be best assured by the installation of test wires from one of the 
 buses to all points of probable highest and lowest rail potential, 
 which arrangement admits of immediate measurement of poten- 
 tial between these points. 
 
 In certain cases, especially in existing plants, the installation 
 of such test wires would involve great cost. Such test wires from 
 all of the important rail points were not required; but it has been 
 ruled that all points of the rail network, to which cables of the 
 same district are now connected,, are to be provided with test 
 wires which have to run to some central point where readings of 
 the differences of potentials between the return points can be 
 taken. 
 
 Wherever the expense involved permits, it is recommended to 
 install test wires not only to the return points but also to the 
 points of highest rail potentials. 
 
 After permanent changes in the operation, the distribution of 
 the potential in the rail network is to be investigated in the same 
 way as after the inauguration of the plant, in order to ascertain 
 whether the new conditions still correspond to the rules. 
 
 In case of temporary changes of short duration in the whole 
 network or parts of the same as, for instance, occasionally some 
 festival, change or repair of tracks, fairs, exhibits, etc., no special 
 measures are to be taken because the short duration of the influ- 
 ence will cause no noticeable damage even when the limits of 
 these rules are exceeded. 
 
 The yearly investigation of the rail joints, as required by the 
 rules, is also to be recommended with regard to the reduction of 
 
176 EUROPEAN PRACTICE 
 
 losses of energy. For these measurements an apparatus may be 
 used which allows of the comparison of the drop in potentials 
 across the joint with one of the adjoining uninterrupted rails so 
 that the measurement may be taken during the operation. Joints 
 of a resistance higher than that of an uninterrupted rail of 10 m. 
 length are immediately to be repaired. The total resistance, as 
 found by the measurement of the single joints, must not exceed 
 the value which has been assumed during the projection of the 
 plant (compare Section 2, paragraph 2). 
 
 Should it result during operation that rail joints are of a higher 
 resistance than that assumed in the designing, it is permissible 
 to abstain from a reconstruction of the joints as long as the 
 permissible difference of potentials in the rails is not exceeded, 
 even with these higher resistances. The established limits of 
 20% increase of the resistance of the uninterrupted rail by the 
 bonds must not be exceeded in any case. 
 
 FRANCE REGULATIONS BY MINISTER OF PUBLIC WORKS 
 
 CIRCULAR AND ORDER OF THE MINISTER OF PUBLIC WORKS (FRANCE) OF 
 MARCH 21, 1911, ESTABLISHING THE TECHNICAL CONDITIONS WHICH ELECTRICAL 
 DISTRIBUTION SYSTEMS MUST SATISFY IN ORDER TO CONFORM TO THE LAW OF 
 JUNE 15, 1906. 
 
 Regulations Relative to the Construction of Structures for Electric Railways 
 Using Direct Currents. 
 
 Right of Way. 
 
 When the rails are used as conductors, all necessary measures 
 should be taken to guard against the harmful action of stray cur- 
 rents, on metallic structures, such as the tracks of railways, the 
 water and gas pipes, the telegraph or telephone lines and all other 
 electric conductors, etc. 
 
 To this end the following regulations shall be applied: 
 
 1. The conductance of the tracks shall be known to be in the 
 best possible condition, especially in regard to the joints, whose 
 resistance should not exceed, in each case, that of 10 meters of 
 the normal track. 
 
 The management is required to verify periodically this con- 
 ductance and to place the results obtained on file, which shall be 
 accessible to the administration upon demand. 
 
 2. The drop in potential in the rails, measured upon a length 
 of track of 1 kilometer taken arbitrarily upon any section of the 
 system, should not exceed an average value of 1 volt for the operat- 
 ing period of the normal car schedule. 
 
 3. The feeders tied into the track shall be insulated. 
 
EUROPEAN PRACTICE 177 
 
 4. Where the tracks contain switches or crossings, the conduct- 
 ance shall be maintained by special work. 
 
 5. When the track crosses a metallic structure, it should be 
 electrically insulated, as much as possible, throughout the length 
 of the structure. 
 
 6. As long as no metallic structure is in the neighborhood of the 
 tracks, a drop in potential greater than that fixed in paragraph 
 2 may be allowed, upon the condition that no damage will result, 
 and particularly no trouble to telegraphic or telephonic communi- 
 cation, and none to railway signals. 
 
 7. The owner of the distribution system shall be required to 
 make the installations necessary to enable the administration to 
 verify the fulfillment of the provisions of this article; it should 
 particularly provide, whenever necessary, for pilot wires to be 
 installed between designated points of the distribution system. 
 
 Protection oj Neighboring Aerial Lines 
 
 At all points where the lines feeding the traction system cross 
 other distribution lines, or telegraph or telephone lines, the sup- 
 ports should be established with a view to protect mechanically 
 these lines against contact with the aerial conductors feeding the 
 traction system. 
 
 In all cases, measures shall be taken to prevent the trolley wire 
 touching the neighboring lines. 
 
 ENGLAND BRITISH BOARD OF TRADE REGULATIONS 
 
 REGULATIONS MADE BY THE BOARD OF TRADE UNDER THE PROVISIONS OF 
 SPECIAL TRAMWAYS ACTS OR LIGHT RAILWAY ORDERS AUTHORIZING "LINES" 
 ON PUBLIC ROADS; FOR REGULATING THE USE OF ELECTRICAL POWER; FOR 
 PREVENTING FUSION OR INJURIOUS ELECTROLYTIC ACTION OF OR ON GAS OR 
 WATER PIPES OR OTHER METALLIC PIPES, STRUCTURES OR SUBSTANCES; AND 
 FOR MINIMIZING AS FAR AS IS REASONABLY PRACTICABLE INJURIOUS INTERFER- 
 ENCE WITH THE ELECTRIC WIRES, LINES, AND APPARATUS OF PARTIES OTHER 
 THAN THE COMPANY, AND THE CURRENTS THEREIN, WHETHER SUCH LINES DO 
 OR DO NOT USE THE EARTH AS A RETURN. 
 
 FIRST MADE, MARCH, 1894. 
 
 REVISED, APRIL, 1903. 
 
 FURTHER REVISED, AUGUST, 1904. 
 
 FURTHER REVISED, MAY, 1908. 
 
 FURTHER REVISED, APRIL, 1910. 
 
 FURTHER REVISED, SEPTEMBER, 1912. 
 
 Regulations 
 
 1. Any dynamo used as a generator shall be of such pattern 
 and construction as to be capable of producing a continuous 
 current without appreciable pulsation. 
 
178 EUROPEAN PRACTICE 
 
 2. One of the two conductors used for transmitting energy from 
 the generator to the motors shall be in every case insulated from 
 earth, and is hereinafter referred to as the "line"; the other may 
 be insulated throughout, or may be uninsulated in such parts and 
 to such extent as is provided in the following regulations, and is 
 hereinafter referred to as the "return." 
 
 NOTE: The Board of Trade will be prepared to consider 
 the issue of regulations for the use of alternating currents for 
 electrical traction on application. 
 
 3. Where any rails on which cars run or any conductors laid 
 between or within three feet of such rails form any part of a return, 
 such part may be uninsulated. All other returns or parts of a 
 return shall be insulated, unless of such sectional area as will re- 
 duce the difference of potential between the ends of the uninsulated 
 portion of the return below the limit laid down in Regulation 7. 
 
 4. When any uninsulated conductor laid between or within 
 three feet of the rails forms any part of a return, it shall be elec- 
 trically connected to the rails at distances apart not exceeding 
 100 feet by means of copper strips, having a sectional area of at 
 least one-sixteenth of a square inch, or by other means of equal 
 conductivity. 
 
 5. (a) When any part of 'a return is uninsulated it shall be 
 connected with the negative terminal of the generator, and in 
 such case the negative terminal of the generator shall also be 
 directly connected, through the current-indicator hereinafter 
 mentioned, to two separate earth connections which shall be 
 placed not less than 20 yards apart. 
 
 (b) The earth connections referred to in this regulation shall 
 be constructed, laid and maintained, so as to secure electrical 
 contact with the general mass of earth, and so that, if possible, 
 an electromotive force, not exceeding four volts, shall suffice to 
 produce a current of at least two amperes from one earth con- 
 nection to the other through the earth, and a test shall be made 
 once in every month to ascertain whether this requirement is 
 complied with. 
 
 (c) Provided that in place of such two earth connections the 
 Company may make one connection to a main for water supply 
 of not less than three inches internal diameter, with the consent 
 of the owner thereof, and of the person supplying the water, and 
 provided that where, from the nature of the soil or for other 
 reasons, the Company can show to the satisfaction of the Board 
 of Trade that the earth connections herein specified cannot be 
 
EUROPEAN PRACTICE 179 
 
 constructed and maintained without undue expense, the provi- 
 sions of this regulation shall not apply. 
 
 (d) No portion of either earth connection shall be placed within 
 six feet of any pipe except a main for water supply of not less than 
 three inches internal diameter, which is metallically connected to 
 the earth connections with the consents hereinbefore specified. 
 
 (e) When the generator is at a considerable distance from the 
 tramway the uninsulated return shall be connected to the negative 
 terminal of the generator by means of one or more insulated return 
 conductors, and the generator shall have no other connection with 
 earth ; and in such case the end of each insulated return connected 
 with the uninsulated return shall be connected also through a 
 current indicator to two separate earth connections, or with the 
 necessary consents to a main for water supply, or with the like 
 consents to both in the manner prescribed in this regulation. 
 
 (/) The current indicator may consist of an indicator at the 
 generating station connected by insulated wires to the terminals 
 of a resistance interposed between the return and the earth con- 
 nection or connections, or it may consist of a suitable low-resist- 
 ance maximum demand indicator. The said resistance, or the 
 resistance of the maximum demand indicator, shall be such that 
 the maximum current laid down in Regulation 6 (I) shall produce 
 a difference of potential not exceeding one volt between the ter- 
 minals. The indicator shall be so constructed as to indicate cor- 
 rectly the current passing through the resistance when connected 
 to the terminals by the insulated wires before-mentioned. 
 
 6. When the return is partly or entirely uninsulated the Com- 
 pany shall in the construction and maintenance of the tramway 
 (a) so separate the uninsulated return from the general mass of 
 earth, and from any pipe in the vicinity; (b) so connect together 
 the several lengths of the rails ; (c) adopt such means for reducing 
 the difference produced by the current between the potential of 
 the uninsulated return at any one point and the potential of the 
 uninsulated return at any other point; and (d) so maintain the 
 efficiency of the earth connections specified in the preceding regu- 
 lations as to fulfill the following conditions, viz: 
 
 (I) That the current passing from the earth connections 
 through the indicator to the generator or through the resist- 
 ance to the insulated return shall not at any time exceed 
 either two amperes per mile of single tramway line or five 
 per cent of the total current output of the station. 
 
 (II) That if at any time and at any place a test be made 
 
180 EUROPEAN PRACTICE 
 
 by connecting a galvanometer or other current-indicator to 
 
 the uninsulated return and to any pipe in the vicinity, it shall 
 
 always be possible to reverse the direction of any current 
 
 indicated by interposing a battery of three Leclanche cells 
 
 connected in series if the direction of the current is from the 
 
 return to the pipe, or by interposing one Leclanche cell if the 
 
 direction of the current is from the pipe to the return. 
 
 The owner of any such pipe may require the Company to permit 
 
 him at reasonable times and intervals to ascertain by test that the 
 
 conditions specified in (II) are complied with as regards his pipe. 
 
 7. When the return is partly or entirely uninsulated a con- 
 tinuous record shall be kept by the Company of the difference of 
 potential during the working of the tramway between points on 
 the uninsulated return. If at any time such difference of potential 
 between any two points exceeds the limit of seven volts, the Com- 
 pany shall take immediate steps to reduce it below that limit. 
 
 8. The current density in the rails shall not exceed nine am- 
 peres per square inch of the cross-sectional area. 
 
 9. Every electrical connection with any pipe shall be so arranged 
 as to admit of easy examination, and shall be tested by the Com- 
 pany at least once in every three months. 
 
 10. Trie insulation of the line and of the return when insulated, 
 and of all feeders and other conductors, shall be so maintained 
 that the leakage current shall not exceed one hundredth of an 
 ampere per mile of tramway. The leakage current shall be as- 
 certained not less frequently than once in every week before or 
 after the hours of running when the line is fully charged. If at 
 any time it should be found that the leakage current exceeds one- 
 half of an ampere per mile of tramway, the leak shall be localized 
 and removed as soon as practicable, and the running of the cars 
 shall be stopped unless the leak is localized and removed within 
 24 hours. Provided that where both line and return are placed 
 within a conduit this regulation shall not apply. 
 
 11. The insulation resistance of all continuously insulated cables 
 used for lines, for insulated returns, for feeders, or for other pur- 
 poses, and laid below the surface of the ground, shall not be per- 
 mitted to fall below the equivalent of 10 megohms for a length 
 of one mile. A test of the insulation resistance of all such cables 
 shall be made at least once in each month. 
 
 12. Any insulated return shall be placed parallel to and at a 
 distance not exceeding three feet. from the line when the line and 
 
EUROPEAN PRACTICE 181 
 
 return are both erected overhead, or eighteen inches when they 
 are both laid underground. 
 
 13. In the disposition, connections, and working of feeders, 
 the Company shall take all reasonable precautions to avoid in- 
 jurious interference with any existing wires. 
 
 14. The Company shall so construct and maintain their sys- 
 tem as to secure good contact between the motors and the line and 
 return, respectively. 
 
 15. The Company shall adopt the best means available to 
 prevent the occurrence of undue sparking at the rubbing or rolling 
 contacts in any place and in the construction and use of their 
 generator and motors. 
 
 16. Where the line or return or both are laid in a conduit the 
 following conditions shall be complied with in the construction 
 and maintenance of such conduit. 
 
 (a) The conduit shall be so constructed as to admit of 
 examination of and access to the conductors contained therein 
 and their insulators and supports. 
 
 (b) It shall be so constructed as to be readily cleared of 
 accumulation of dust or other debris, and no such accumula- 
 tion shall be permitted to remain. 
 
 (c) It shall be laid to such falls and so connected to sumps 
 or other means of drainage, as to automatically clear itself 
 of water without danger of the water reaching the level of the 
 conductors. 
 
 (d) If the conduit is formed of metal, all separate lengths 
 shall be so jointed as to secure efficient metallic continuity for 
 the passage of electric currents. Where the rails are used to 
 form any part of the return they shall be electrically connected 
 to the conduit by means of copper strips having a sectional 
 area of at least one-sixteenth of a square inch, or other means 
 of equal conductivity, at distances apart not exceeding 100 
 feet. Where the return is wholly insulated and contained 
 within the conduit, the latter shall be connected to earth at 
 the generating station or sub-station through a high resistance 
 galvanometer suitable for the indication of any contact or 
 partial contact of either the line or the return with the conduit. 
 
 (e) If the conduit is formed of any non-metallic material 
 not being of high insulating quality and impervious to mois- 
 ture throughout, the conductors shall be carried on insulators, 
 the supports for which shall be in metallic contact with one 
 another throughout. 
 
182 EUROPEAN PRACTICE 
 
 (/) The negative conductor shall be connected with earth 
 at the station by a voltmeter and may also be connected with 
 earth at the generating station or substation by an adjust- 
 able resistance and current-indicator. Neither conductor 
 shall otherwise be permanently connected with earth. 
 
 (g) The conductors shall be constructed in sections not 
 exceeding one-half a mile in length, and in the event of a leak 
 occurring on either conductor that conductor shall at once 
 be connected with the negative pole of the dynamo, and shall 
 remain so connected until the leak can be removed. 
 
 (h) The leakage current shall be ascertained daily, before 
 or after the hours of running, when the line is fully charged 
 and if at any time it shall be found to exceed one ampere per 
 mile of tramway, the leak shall be localized and removed as 
 soon as practicable, and the running of the cars shall be 
 stopped unless the leak is localized and removed within 24 
 hours. 
 
 17. The Company shall, so far as may be applicable to their 
 system of working, keep records as specified below. These records 
 shall, if and when required, be forwarded for the information of 
 the Board of Trade. 
 
 Number of cars running. 
 
 Number of miles of single tramway line. 
 
 Daily Records. 
 
 Maximum working current. 
 
 Maximum working pressure. 
 
 Maximum current from the earth plates or water-pipe connec- 
 tions (vide Regulation 6 (&)) where the indicator is at the generat- 
 ing works. 
 
 Fall of potential in return (vide Regulation 7). 
 
 Leakage current (vide Regulation 16 (h)). 
 
 Weekly Records. 
 
 Leakage current (vide Regulation 10). 
 
 Maximum current from the earth plates or water-pipe connec- 
 tions (vide Regulations 6 (I)) where a maximum demand indicator 
 is used. 
 
 Monthly Records. 
 
 Condition of earth connections (vide Regulation 5) . 
 Minimum insulation resistance of insulated cables in megohms 
 per mile (vide Regulation 11). 
 
EUROPEAN PRACTICE 183 
 
 Quarterly Records. 
 
 Conductance of connections to pipes (vide Regulation 9). 
 Occasional Records. 
 
 Specimens of test made under provisions of Regulation 6 (II). 
 Board of Trade, 
 
 7, Whitehall Gardens, S. W. September, 1912. 
 
 SPAIN ELECTRIC LEGISLATION 
 
 LAW OF MARCH 23, 1900. 
 
 TO PREVENT THE RETURN CURRENT OF ELECTRIC TRAMWAY LINES FROM 
 EXERCISING ANY ELECTROLYTIC EFFECTS, THE FOLLOWING MEASURES SHALL BE 
 TAKEN: 
 
 (1) The rails of each one of the tracks are bonded by weld- 
 ing or by connections formed of short copper cables or of 
 equivalent cables made of some other metal, the section of 
 which having to exceed 100 square millimeters per track, and 
 shall be made as large as possible. 
 
 (2) At intervals of 100 meters, or at shorter distances the 
 tracks shall be cross-bonded. 
 
 (3) In case the official inspector should deem it necessary, 
 a cable will have to be stretched in every line, which will 
 have to be intimately connected with both tracks, and 
 
 (4) The dimensions of all cables and wires constituting 
 such system will have to be calculated upon a basis that the 
 potential difference between the generator terminals and the 
 point of the tracks remotest from them will not exceed an 
 amount of seven volts. 
 
CHAPTER 5. 
 ELECTROLYSIS RESEARCH 
 
 FURTHER WORK NECESSARY TO ARRIVE AT AN 
 
 ENGINEERING SOLUTION OF THE 
 
 PROBLEM 
 
 The Committee's conception of an engineering solution of the 
 electrolysis problem is that the railway system and the systems of 
 underground structures shall be so designed, constructed, main- 
 tained, and operated, that the entire problem, caused by the 
 presence of stray currents in the earth, including corrosion of 
 structures, fire and explosion hazards, heating of power cables, 
 and operating losses and difficulties, is solved in the most economi- 
 cal way. 
 
 1. Methods of Testing. 
 
 The Research Sub-committee of the American Committee on 
 Electrolysis, in its investigations, has been constantly confronted 
 with the difficulty that available methods of electrolysis testing do 
 not yield directly, definite information as to the electrolytic con- 
 dition of the affected structures. An electrolysis survey, to be 
 conclusive must, in some cases, show the true polarity of pipe or 
 cable with respect to earth and in other cases it must show the 
 actual density of the current flowing from pipe to earth in any 
 particular locality under investigation, but to determine such 
 polarity, or intensity of current flow, is very difficult. The exist- 
 ing methods of making electrolysis surveys include, among others, 
 measurements of potential differences between pipes and earth, 
 but such measurements, as ordinarily made, are often quite mis- 
 leading. At the present time, therefore, the results that follow 
 the application of any particular method of electrolysis mitiga- 
 tion are sometimes open to question because of the lack of ade- 
 quate test methods. It is evident therefore, that the development 
 of improved means of electrolysis testing whereby the actual cur- 
 rent density of discharge from pipes to earth at any point can be 
 measured is an important preliminary step toward securing definite 
 information on which the solution of the outstanding questions 
 relating to electrolysis protection can be based. The Research 
 Sub-committee now has under investigation certain new methods 
 of electrolysis testing which offer considerable promise in this 
 direction and it is felt that a thorough study and development of 
 184 
 
ELECTROLYSIS RESEARCH 185 
 
 these should be made in the hope of obtaining improved test 
 methods and equipment that will facilitate securing the informa- 
 tion required. It is desirable that these investigations precede 
 further experimental work relating to methods of mitigation. 
 
 2. Effect of Different Rail Voltage Drops. 
 
 It is important to examine the resulting conditions, from an 
 electrolysis standpoint, of different values of voltage drop in rails, 
 particularly in cities or localities where such voltage drops are 
 low, and comparable to those which correspond to maximum 
 economy from the railway standpoint, taking due account of 
 variations in physical conditions in different localities. 
 
 3. Studies of Electric Railway Power Distribution. 
 
 Studies should be made of the costs of various measures de- 
 signed to minimize track drops in order to determine which 
 measures, if any, are best to apply. The application of auto- 
 matic and semi-automatic substations to street railways should 
 be given consideration to determine how far the voltage drop 
 in the rails can be reduced with such a system when developed 
 to the economic limit. In making these cost studies track net- 
 works should be selected where the layout is both favorable and 
 unfavorable for such installations. Studies might also be made 
 of the joint application of insulated negative feeders and auto- 
 matic substations to determine what values of voltage drops in 
 the rails can be obtained at reasonable cost. 
 
 4. Study of Mitigative Measures Applicable to Affected Structures. 
 
 After applying mitigative measures to the railway system, it 
 may be found that in many cases it will still be necessary to reduce 
 further the hazards to underground structures. It is therefore 
 important to study methods of mitigation applicable to the struc- 
 tures themselves, and particularly the quantitative effect of 
 insulating joints in protecting pipes and cables and the applica- 
 tion and maintenance of such a drainage system as will keep all 
 underground structures negative to the earth without involving 
 fire and explosion hazards, and assuming in both cases the railway 
 stray current at a low value. 
 
 5. Determination of Safety Criterion for Pipes Where Positive to 
 
 Earth. 
 
 At the present time there is no reliable criterion as to the actual 
 hazard to underground pipes unless they are at all points negative 
 or neutral to earth at practically all times. Wherever pipes are 
 
186 ELECTROLYSIS RESEARCH 
 
 positive to earth, it is impossible with the present methods of 
 testing to determine the actual degree of corrosion hazard. If 
 however, the development work in connection with methods of 
 measuring current discharge from pipes mentioned in a preceding 
 paragraph should result favorably, it appears probable that such 
 test methods could be used for the purpose of establishing a fairly 
 accurate criterion for a safe condition of underground structures. 
 The Committee feels that this question should be investigated 
 carefully so that anything possible of accomplishment in this 
 direction may be realized. 
 
 6. Self Corrosion. 
 
 When iron pipes are embedded in certain soils, corrosion due to 
 soil conditions or local galvanic action often results in greater or 
 less degree. This phenomenon is commonly known as self corro- 
 sion. Obviously, it is of importance to differentiate between the 
 effects of corrosion due to the action of chemicals in the soil and 
 that due to stray currents, in order that an intelligent procedure 
 can be adopted for remedying the trouble. It is believed that a 
 thorough and systematic study of the question of soil corrosion 
 on cast iron, wrought iron and steel pipes would bring to light 
 information that would be of great value in dealing with the 
 electrolysis problem. Such investigations in order to be of much 
 value should be extended over a period of years. 
 
 7. Fire and Explosion Hazards on Gas and Oil Pipes. 
 
 In addition to preventing corrosion, there is the closely related 
 problem of protecting against fires and explosions due to electric 
 currents on gas or oil pipes. At the present time no definite 
 information is available as to what limiting currents can safely 
 be permitted on such pipe systems. It is important to investigate 
 this question, both statistically and experimentally in order to 
 evaluate this hazard. 
 
 8. Heating of Power Cables Due to Stray Currents on Sheaths. 
 
 In view of the fact that it is common practice to electrically 
 drain the lead sheaths of power cables to protect them from corro- 
 sion, and since the currents on the sheaths may be of considerable 
 magnitude, reducing the current carrying capacity of the conduc- 
 tors, it is important to determine the limitations that should be 
 imposed on such currents in order not to cause serious heating, 
 and hence undue reduction in current carrying capacity of the 
 cables. 
 
ELECTROLYSIS RESEARCH 187 
 
 Summary. As the Committee now views it, a research of some 
 magnitude is necessary to secure further information needed for 
 an engineering solution of the problem, to comprise the following: 
 
 1. Development of practical means for measuring current 
 density across contact surfaces of pipes and earth. Such 
 measurements are especially necessary if structures are not 
 kept negative to earth. 
 
 2. Development of practical means for accurately deter- 
 mining the polarity of structures and adjacent earth, in such 
 a way as to eliminate galvanic effects. 
 
 3. Study of the relation of different values of voltage drop 
 in the track to stray current from rails, including the large 
 variations of this relation under different conditions, and the 
 effects of such stray currents on underground utilities and 
 railway structures. 
 
 4. Cost studies of street railway systems and different 
 methods of power supply to determine the minimum values 
 of track voltage drop consistent with economic operation in 
 various locations. 
 
 5. Quantitative effect of insulating joints in protecting 
 pipes and cables, assuming railway stray current at low values. 
 
 6. Detailed study of the application and maintenance of 
 such a drainage system as will keep all underground struc- 
 tures negative to earth. Such studies to include the effect 
 of drainage on corrosion of subsurface and railway structures 
 and its effect on producing fires and explosions. 
 
 7. Comparison of 5 and 6. 
 
 8. Investigation of the distribution of current flowing 
 from pipe to adjacent earth for the purpose of determining 
 whether a diversity factor can be established, i.e., the relation 
 between maximum and average current density. 
 
 9. Continuing study of joint corrosion. 
 
 10. Study of soil and galvanic corrosion with particular 
 reference to differentiating them from the effects of stray 
 currents. 
 
 11. Setting limit of current on gas and oil pipes to avoid 
 fire and explosion hazard. 
 
 12. Setting limit of current on power cable sheaths to 
 avoid overheating. 
 
 BIBLIOGRAPHY 
 
 In compiling the following bibliography no attempt has been 
 made to list the literature on the subject of electrolysis in its 
 
188 ELECTROLYSIS RESEARCH 
 
 entirety. This bibliography may be considered as a selected 
 list of such contributions to the subject known to the committee 
 as in its opinion are of the most importance at the present time. 
 The committee, however, does not sponsor the articles here listed 
 nor does it present them as comprising a complete discussion 
 of the subject. 
 
 General 
 
 Corrosion of Iron Pipes by Action of Electric Railway Currents. 
 
 Dugald C. Jackson. Journal of Association of Engineering 
 
 Societies, September, 1894. 
 Electrolytic Corrosion of Iron by Direct Current in Street Soils. 
 
 Albert F. Ganz. Trans. A. I. E. E., Vol. XXXI, page 1167. 
 
 1912. 
 
 Stray Currents from Electric Railways. Carl Michalke. Trans- 
 lated and edited by Otis Allen Kenyon, McGraw Publishing 
 
 Company, New York, N. Y. 1906. 
 Electrolytic Corrosion of Iron in Soils. Burton McCollum and 
 
 K. H. Logan. Bureau of Standards Technologic Paper No. 
 
 25, June, 1913. 
 Effects of Electrolysis on Engineering Structures. Albert F. 
 
 Ganz. Trans. International Engineering Congress, San 
 
 Francisco, 1915. 
 
 Electrolysis and Its Mitigation. E. B. Rosa and Burton Mc- 
 Collum. Bureau of Standards Technologic Paper No. 52, 
 
 Nov., 1918. 
 Electrolysis, Troubles Caused Thereby and Remedies That May 
 
 be Applied. Albert F. Ganz, Journal New England Water 
 
 Works Association. Vol. XXXI, No. 2, 1917. 
 Report of Gas Association Committee on Electrolysis. J. D. 
 
 Von Maur, Chairman. Technical Section Sessions, American 
 
 Gas Association, 1919. 
 
 Electrolytic Corrosion of Pipes and Cables 
 Destructive Effect of Electric Currents on Subterranean Metal 
 
 Pipes. Isaiah H. Farnham, Trans. A. I. E. E., 1894. 
 Electrolysis of Water Pipes. Charles A. Stone and Howard C. 
 
 Forbes. New England Water Works Association, Vol. 9, 
 
 1894-5. 
 Topical Discussion on Electrolysis. Proc. New England Water 
 
 Works Association, Vol. XX, 1905. 
 Earth Resistance and Its Relation to Electrolysis of Underground 
 
 Structures. Burton McCollum and K. H. Logan. Bureau 
 
 of Standards Technologic Paper, No. 26. 
 
ELECTROLYSIS RESEARCH 189 
 
 Surveys and Measurements 
 
 Measuring Stray Currents in Underground Pipes. Carl Hering. 
 A. I. E. E., June, 1912, pp. 1147-61. 
 
 Electrolysis Surveys. Albert F. Ganz. Engrg. Rec., 1908, V. 57, 
 p. 261. 
 
 Methods of Making Electrolysis Surveys. Burton McCollum and 
 G. H. Ahlborn, Bureau of Standards Technologic Paper No. 
 2&, 1916. 
 
 Bureau of Standards Studies return Circuit Conditions in Milwau- 
 kee. E. R. Shepard. Elec. Ry. Journal, April 19, 1919, pp. 
 770-772. 
 
 Electrolysis Surveys and Their Significance. Report of the 1920 
 Electrolysis Committee of the American Gas Association, 
 L. A. Hazeltine, Chairman. Technical Section Sessions. 
 
 Alternating Current and Periodic Current Electrolysis 
 
 Alternating-Current Electrolysis. J. L. R. Hay den. Trans. 
 A. I. E. E., 1907. Vol. 26, part I. 
 
 Influence of Frequency of Alternating or Infrequently Reversed 
 Current on Electrolytic Corrosion. Burton McCollum and 
 G. H. Ahlborn. Bureau of Standards Technologic Paper 
 No. 72, 1916. 
 
 Discussion of McCollum and Ahlborn Paper, New York. March 
 10, 1916. Proc. A. I. E. E. July, 1916. 
 
 Electrolytic Corrosion of Lead by Continuous and Periodic Cur- 
 rents. E. R. Shepard. American Electro-chemical Society, 
 1921. 
 
 Reinforced Concrete 
 
 Corrosion of Iron Embedded in Concrete. Guy F. Schaffer. 
 
 Engineering Record, July 30, 1910. 
 Electrolytic Corrosion of Iron and Steel in Concrete. A. A. 
 
 Knudson. Trans. A. L E. E., v. 26, part 1, p. 231. 
 Electrolysis in Concrete. E. B. Rosa, Burton McCollum, and 
 
 O. S. Peters. Bureau of Standards Technologic Paper No. 
 
 18, Mar., 1913. 
 Preventing Electrolysis of Iron in Concrete. W. A. Delmar and 
 
 D. C. Woodbury. Electrical World, November 10, 1917. 
 
 Track Construction, Track Leakage, and Rail Bonding 
 
 Modern Practice in the Construction and Maintenance of Rail 
 Joints and Bonds in Electric Railways. E. R. Shepard, 
 Bureau of Standards Technologic Paper No. 62, 1920. 
 
190 ELECTROLYSIS RESEARCH 
 
 Leakage of Currents from Electric Railways. Burton McCollum 
 
 and H. K. Logan, Bureau of Standards Technologic Paper 
 
 No. 63, 1916. 
 Data on Electric Railway Track Leakage. G. H. Ahlborn, Bureau 
 
 of Standards Technologic Paper No. 75, 1916. 
 Leakage Resistance of Street Railway Roadbeds and its Relation 
 
 to Electrolysis of Underground Structures. E. R. Shepard. 
 
 Bureau of Standards Technologic Paper No. 127. 1919. 
 
 Insulated Negative Feeders 
 
 Means for Preventing Electrolysis of Buried Metal Pipes. Isaiah 
 H. Farnham. Cassiers Magazine, August, 1895. 
 
 Some Theoretical Notes on the Reduction of Earth Currents 
 from Electric Railway Systems, by Means of Negative 
 Feeders. George I. Rhodes Trans. A. I. E. E., Vol. XXVI, 
 p. 247, 1907. 
 
 Special Studies in Electrolysis Mitigation II. E. B. Rosa, Burton 
 McCollum and K. H. Logan. Bureau of Standards Tech- 
 nologic Paper No. 32, 1913. 
 
 Special Studies in Electrolysis Mitigation III. Burton McCollum 
 and G. H. Ahlborn. Bureau of Standards Technologic Paper 
 No. 54, 1916. 
 
 Electrolysis from Stray Electric Currents. Albert F. Ganz. 
 Trans. A. I. E. E., Vol. XXXI, p. 1167, 1912. 
 
 Automatic Substations 
 
 Automatic Substations on the North Shore Line. C. H. Jones, 
 
 Electric Railway Journal, Jan. 11, 1919, 53: 84-90. 
 Year of the Automatic Substation at Butte. E. J. Nash, Electric 
 
 Railway Journal, March 22, 1919. 53: 565-7. 
 Second Year of Automatic Substation Operation at Butte. E. J. 
 
 Nash, Electric Railway Journal, Jan. 24, 1920. 55: 202. 
 Automatic Railway Substations. F. W. Peters: Journal A. I. E. E 
 
 March, 1920. 39:267-74. Excerpts Elec. Ry. Journal, 
 
 March 13, 1920. 55:518-19; Abstract Elec. Ry. Journal, 
 
 June 13, 1920. 55:519-21. 
 Experience Shows Economy of Automatic Operation. Electrical 
 
 World, March 20, 1920. 
 Automatic Stations for Heavy City Service. R. J. Wensley, 
 
 Journal A. I. E. E., April, 1920. pp. 359-364. 
 Automatic Substations at Des Moines. F. C. Chambers, Elec. 
 
 Ry. Journal, April 10, 1920, 55:738-44. 
 
ELECTROLYSIS RESEARCH 191 
 
 The Automatic Substation in Electrolysis Mitigation. E. R. 
 vShepard, Electric Railway Journal, April 30, 1921. 
 
 Three- Wire Operation 
 
 Three-wire System in Los Angeles. S. H. Anderson, Electric 
 
 Railway Journal. February 26, 1916. 
 Line Drops and Rail Potentials Reduced by Three- Wire System 
 
 in Omaha. E. H. Hagensick, Elec. Ry. Journal, November 
 
 10, 1917. 
 Sectionalization of Overhead Wire for Three-Wire Operation. 
 
 E. R. Shepard, Elec. Ry. Journal. December 8, 1917. 
 Electrolysis Mitigation in Winnipeg. W. Nelson Smith, Elec. 
 
 Ry. Journal, March 26, 1921. 
 
 Insulating Pipe Coverings 
 
 Comparative Values of Various Coatings and Coverings for the 
 Prevention of Soil and Electrolytic Corrosion of Iron Pipe. 
 Robert B. Harper, Proc. Illinois Gas Association. Vol. 5, 
 1909. Also American Gas Light Journal, v. 91, 1909. 
 
 Insulation of Pipes as a Protection Against Electrolysis. Albert 
 
 F. Ganz., Engineering Record, 1909, V. 60, p. 582. Also 
 Pro. Am. Gas Inst. about same date. 
 
 Surface Insulation of Pipes as a Means of Preventing Electrolysis. 
 Burton McCollum and 0. S. Peters, Bureau of Standards 
 Technologic Paper No. 15, 1914. 
 
 Insulating Joints 
 
 Insulating Couplings for Protecting Pipe Systems from Elec- 
 trolysis. William Brophy and A. R. Gray, Am. Gas Light 
 Journal, 1904, V. 80, p. 91. 
 
 Flexible High Pressure Pipe Joint. Engrg. Rec., V. 62, p. 307. 
 1910. 
 
 Cement Joints for Cast Iron Water Mains in Los Angeles. Cement 
 World, February, 1916. 
 
 Pipe and Cable Drainage 
 
 Bonding Lead Covered Cables to Prevent Electrolysis. W. G. 
 
 Middleton. Elec. Rev. and West Electrn., V. 57, p. 423. 
 
 1910. 
 Drainage if Necessary vs. Negative Feeder Electrolysis Protection. 
 
 D. W. Roper, Elec. Ry. Journal, Dec. 7, 1918. 
 
192 ELECTROLYSIS RESEARCH 
 
 Discussion of preceding articles. Elam Miller, H. C. Button, and 
 D. W. Roper, Elec. Ry. Journal, April 5, 1919. 
 
 Legal Aspects 
 
 The Law Relating to Conflicting Uses of Electricity and Electroly- 
 sis. George F. Deiser. T. & J. W. Johnson Co., Phila- 
 delphia, Pa. 1911. 
 
 Electrolysis of Underground Conductors. George F. Sever. 
 Trans. International Electrical Congress, Vol. 3, p. 666. 1904. 
 
APPENDIX 
 
 TABLE 5 
 
 CURRENT DATA FOR STEEL RAILS* 
 
 Based on a resistivity of 0.0003 ohm per pound-foot, this being equivalent to 
 about 11 times the resistivity of copper. 
 
 Weight 
 . (Ibs. per yd.) 
 
 Current for 1m. v. 
 on 1 ft. (amperes) 
 
 Weight 
 (Ibs. per yd.) 
 
 Current for 1 m. v. 
 on 1 ft. (amperes) 
 
 60 
 
 66.7 
 
 110 
 
 122.0 
 
 65 
 
 72.2 
 
 115 
 
 128.0 
 
 70 
 
 77.8 
 
 120 
 
 133.0 
 
 75 
 
 83.3 
 
 125 
 
 139.0 
 
 80 
 
 88.9 
 
 1 130 
 
 144.0 
 
 85 
 
 94.4 
 
 135 
 
 150.0 
 
 90 
 
 100.0 
 
 140 
 
 156.0 
 
 95 
 
 106.0 
 
 145 
 
 161.0 
 
 100 
 
 111.0 
 
 150 
 
 167.0 
 
 105 
 
 117.0 
 
 
 
 * Does not include rail joints. 
 
 TABLE 6A 
 
 CURRENT DATA FOR PIPES 
 CAST IRON 
 
 
 A.W.W.A. standard 
 
 A.W.W.A. standard 
 
 
 Class A 
 
 Class B 
 
 Nominal 
 
 
 
 inside 
 
 
 
 
 
 diameter 
 
 
 Current 
 
 
 Current 
 
 (inches) 
 
 Weight 
 
 for 1 mv. 
 
 Weight 
 
 for 1 mv. 
 
 
 pounds 
 
 on 1 ft. 
 
 pounds 
 
 on 1 ft. 
 
 
 per foot 
 
 (amperes) 
 
 per foot 
 
 (amperes) 
 
 3 
 
 13.04 
 
 10.6 
 
 14.60 
 
 11.9 
 
 4 
 
 18.03 
 
 14.7 
 
 20.06 
 
 16.4 
 
 6 
 
 27.90 
 
 22.7 
 
 31.14 
 
 25.4 
 
 8 
 
 38.74 
 
 31.6 
 
 42.68 
 
 34.8 
 
 10 
 
 51.95 
 
 42.3 
 
 58.80 
 
 47.9 
 
 12 
 
 66.90 
 
 55.0 
 
 76.44 
 
 62.0 
 
 14 
 
 82.33 
 
 67.0 
 
 94.82 
 
 77.0 
 
 16 
 
 98.75 
 
 81.0 
 
 114.70 
 
 94.0 
 
 18 
 
 118.10 
 
 96.0 
 
 137.70 
 
 112.0 
 
 20 
 
 137.2 
 
 112.0 
 
 163.20 
 
 133.0 
 
 24 
 
 186.5 
 
 152.0 
 
 217.10 
 
 177.0 
 
 30 
 
 265.1 
 
 216.0 
 
 312.6*0 
 
 255.0 
 
 36 
 
 357.8 
 
 292.0 
 
 419.00 
 
 341.0 
 
 42 
 
 465.6 
 
 379.0 
 
 541.50 
 
 441.0 
 
 48 
 
 607.7 
 
 495.0 
 
 688.50 
 
 562.0 
 
 54 
 
 730.2 
 
 596.0 
 
 842.80 
 
 685.0 
 
 60 
 
 835.6 
 
 680.0 
 
 1,012.00 
 
 826.0 
 
 72 
 
 1,169.0 
 
 952.0 
 
 1,416.00 
 
 1,150.0 
 
 84 
 
 1,141.0 
 
 1,177.0 
 
 1,860.00 
 
 1,515.0 
 
 193 
 
194 
 
 APPENDIX 
 
 TABLE 6A (Continued) 
 CAST IRON 
 
 
 A.W.W.A. standard 
 
 A.W.W.A. standard 
 
 
 Class C. 
 
 Class D. 
 
 Nominal 
 
 
 
 Inside 
 
 
 
 
 
 Diameter 
 
 
 Current 
 
 
 Current 
 
 (inches) 
 
 Weight 
 
 for 1 mv. 
 
 Weight 
 
 for 1 mv. 
 
 
 pounds 
 
 on 1 ft. 
 
 pounds 
 
 on 1 ft. 
 
 
 per foot 
 
 (amperes) 
 
 per foot 
 
 (amperes) 
 
 3 
 
 15.47 
 
 12.6 
 
 16.37 
 
 13.2 
 
 4 
 
 21.27 
 
 17.3 
 
 22.83 
 
 18.5 
 
 6 
 
 32.93 
 
 26.8 
 
 35.30 
 
 28.8 
 
 8 
 
 47.97 
 
 39.1 
 
 51.16 
 
 41.7 
 
 10 
 
 65.66 
 
 - 54.0 
 
 71.54 
 
 58.0 
 
 12 
 
 85.26 
 
 70.0 
 
 93.59 
 
 76.0 
 
 14 
 
 108.0 
 
 88.0 
 
 119.1 
 
 97.0 
 
 16 
 
 133.3 
 
 109.0 
 
 147.5 
 
 120.0 
 
 18 
 
 162.4 
 
 132.0 
 
 178.4 
 
 145.0 
 
 20 
 
 190.9 
 
 156.0 
 
 212.4 
 
 173.0 
 
 '24 
 
 257.7 
 
 210.0 
 
 286.2 
 
 233.0 
 
 30 
 
 367.5 
 
 300.0 
 
 421.4 
 
 344.0 
 
 36 
 
 499.8 
 
 407.0 
 
 580.7 
 
 474.0 
 
 42 
 
 656.6 
 
 535.0 
 
 762.0 
 
 621.0 
 
 48 
 
 833.0 
 
 680.0 
 
 960.4 
 
 780.0 
 
 I 54 
 
 1,041.0 
 
 848.0 
 
 1,227.0 
 
 1,000.0 
 
 60 
 
 1,220.0 
 
 990.0 
 
 1,458.0 
 
 1,190.0 
 
 72 
 
 1,744.0 
 
 1,430.0 
 
 
 
APPENDIX 
 
 195 
 
 TABLE 6A (Continued} 
 CAST IRON 
 
 
 New England W.W.A. 
 
 New England W.W.A. 
 
 
 standard Class A. 
 
 standard Class B. 
 
 Nominal 
 
 
 
 inside 
 
 
 
 
 
 diameter 
 
 
 Current 
 
 
 Current 
 
 (inches) 
 
 Weight 
 
 for 1 mv. 
 
 Weight 
 
 for 1 mv. 
 
 
 pounds 
 
 on 1 ft. 
 
 pounds 
 
 on 1 ft. 
 
 
 per foot 
 
 (amperes) 
 
 per foot 
 
 (amperes) 
 
 4 
 
 14 89 
 
 12.1 
 
 
 
 6 
 
 24.32 
 
 19 9 
 
 
 
 8 
 
 35.58 
 
 29.0 
 
 
 
 10 
 
 49.04 
 
 40.0 
 
 52^03 
 
 "42:i' 
 
 12 
 
 61.14 
 
 50.0 
 
 65.92 
 
 54.0 
 
 14 
 
 76.85 
 
 63.0 
 
 82.41 
 
 67.0 
 
 16 
 
 90.98 
 
 74.0 
 
 98.95 
 
 81.0 
 
 18 
 
 104.5 
 
 85.0 
 
 115.2 
 
 94.0 
 
 20 
 
 121.9 
 
 99.0 
 
 133.7 
 
 109.0 
 
 24 
 
 155.6 
 
 127.0 
 
 174.4 
 
 142.0 
 
 30 
 
 215.3 
 
 176.0 
 
 244.8 
 
 200.0 
 
 36 
 
 287.0 
 
 234.0 
 
 326.0 
 
 266.0 
 
 42 
 
 368.4 
 
 300.0 
 
 422.1 
 
 344.0 
 
 48 
 
 459.3 
 
 374.0 
 
 530.2 
 
 432.0 
 
 54 
 
 559.8 
 
 456.0 
 
 650.3 
 
 530.0 
 
 60 
 
 664.0 
 
 541.0 
 
 782.3 
 
 640.0 
 
196 
 
 APPENDIX 
 
 TABLE 6A (Continued] 
 CAST IRON 
 
 
 New England W.W.A. 
 Standard Class C. 
 
 New England W.W.A. 
 Standard Class D. 
 
 Nominal 
 
 
 
 Inside 
 
 
 
 
 
 Diameter 
 
 
 Current 
 
 
 Current 
 
 (inches) 
 
 Weight 
 
 for 1 mv. 
 
 Weight 
 
 for 1 mv. 
 
 
 pounds 
 
 on 1 ft. 
 
 pounds 
 
 on 1 ft. 
 
 
 per foot 
 
 (amperes) 
 
 per foot 
 
 (amperes) 
 
 4 
 
 15.7 
 
 12.8 
 
 
 
 6 
 
 26.72 
 
 21.8 
 
 
 
 8 
 
 40.38 
 
 32 9 
 
 
 
 10 
 
 54.99 
 
 44.8 
 
 57.94 
 
 47.2 
 
 12 
 
 70.67 
 
 58.0 
 
 75.39 
 
 61.0 
 
 14 
 
 87.97 
 
 72.0 
 
 94.85 
 
 77.0 
 
 16 
 
 106.9 
 
 87.0 
 
 114.8 
 
 93.0 
 
 18 
 
 127.4 
 
 104.0 
 
 138.0 
 
 112.0 
 
 20 
 
 147.6 
 
 120.0 
 
 161.4 
 
 132.0 
 
 24 
 
 196.3 
 
 160.0 
 
 215.3 
 
 175.0 
 
 30 
 
 277.7 
 
 226.0 
 
 307.3 
 
 250.0 
 
 36 
 
 373.3 
 
 304.0 
 
 412.3 
 
 336.0 
 
 42 
 
 481.1 
 
 392.0 
 
 538.9 
 
 439.0 
 
 48 
 
 608.0 
 
 495.0 
 
 678.9 
 
 552.0 
 
 54 
 
 749.5 
 
 610.0 
 
 839.9 
 
 684.0 
 
 60 
 
 911.5 
 
 740.0 
 
 1,029.7 
 
 840.0 
 
APPENDIX 
 
 197 
 
 TABLE 6B 
 STEEL PIPE 
 
 XT " 1 
 
 Standard 
 
 Extra Strong 
 
 Nominal 
 inside 
 diameter 
 (inches) 
 
 Weight 
 pounds 
 
 Current 
 for 1 mv. 
 on 1 ft. 
 
 Weight 
 pounds 
 
 Current 
 for 1 mv. 
 on 1 ft. 
 
 
 per foot 
 
 (amperes) 
 
 per foot 
 
 (amperes) 
 
 0.125 
 
 0.24 
 
 1.11 
 
 0.31 
 
 1.44 
 
 0.25 
 
 0.42 
 
 1.95 
 
 0.54 
 
 2.50 
 
 0.375 
 
 0.57 
 
 2.64 
 
 0,74 
 
 3.43 
 
 0.50 
 
 0.85 
 
 3 94 
 
 1 09 
 
 50 
 
 0.75 
 
 1.13 
 
 5.2 
 
 1.47 
 
 6.8 
 
 1 00 
 
 1 68 
 
 7.8 
 
 2.17 
 
 10.1 
 
 1 25 
 
 2.27 
 
 10.5 
 
 3.00 
 
 13.9 
 
 1.50 
 
 2.72 
 
 12.6 
 
 3.63 
 
 16.8 
 
 2.00 
 
 3.65 
 
 16.9 
 
 5.02 
 
 23.3 
 
 2.50 
 
 5.79 
 
 26.8 
 
 7.66 
 
 35.5 
 
 3.00 
 
 7.58 
 
 35.1 
 
 10.25 
 
 47.5 
 
 3.50 
 
 9.11 
 
 42.2 
 
 12.51 
 
 58.0 
 
 4.00 
 
 10.79 
 
 50.0 
 
 14.98 
 
 69.0 
 
 4.50 
 
 12.54 
 
 58.0 
 
 17.61 
 
 82.0 
 
 5.00 
 
 14.62 
 
 68.0 
 
 20.78 
 
 96.0 
 
 6.00 
 
 18.97 
 
 88.0 
 
 28.57 
 
 132.0 
 
 7.00 
 
 23.54 
 
 109.0 
 
 38.05 
 
 176.0 
 
 8.00 
 
 24.70 
 
 114.0 
 
 43.39 
 
 201.0 
 
 8 00 
 
 28 55 
 
 132 
 
 
 
 9.00 
 
 33.91 
 
 157.0 
 
 "48'73 
 
 226.0 
 
 10.00 
 
 31.20 
 
 145.0 
 
 54.74 
 
 254.0 
 
 10.00 
 
 34.24 
 
 159.0 
 
 
 
 10.00 
 
 40.48 
 
 188.0 
 
 
 
 11.00 
 
 45.56 
 
 211.0 
 
 60.08 
 
 278.0 
 
 12.00 
 
 43.77 
 
 203.0 
 
 65.42 
 
 303.0 
 
 12.00 
 
 49.56 
 
 230.0 
 
 
 
 13.00 
 
 54.57 
 
 253.0 
 
 72.09 
 
 334.0 
 
 14.00 
 
 58.57 
 
 271.0 
 
 77.43 
 
 359.0 
 
 15.00 
 
 62.58 
 
 290.0 
 
 82.77 
 
 383.0 
 
198 
 
 APPENDIX 
 
 TABLE *6C 
 WROUGHT IRON PIPE 
 
 
 Standard 
 
 Extra Strong 
 
 Nominal 
 Inside 
 diameter 
 (inches) 
 
 Weight 
 pounds 
 
 Current 
 for 1 mv. 
 on 1 ft. 
 
 Weight 
 pounds 
 
 Current 
 for 1 mv. 
 on 1 ft. 
 
 
 per foot 
 
 (amperes) 
 
 per foot 
 
 (amperes) 
 
 0.125 
 
 0.24 
 
 1.15 
 
 0.29 
 
 1.39 
 
 0.25 
 
 0.42 
 
 2 01 
 
 0.54 
 
 2.58 
 
 0.375 
 
 0.56 
 
 2.68 
 
 0.74 
 
 3.54 
 
 0.50 
 
 0.84 
 
 4.02 
 
 1.09 
 
 5.2 
 
 0.75 
 
 1 12 
 
 5.4 
 
 1.39 
 
 6.6 
 
 1.0 
 
 1.67 
 
 8.0 
 
 2.17 
 
 10.4 
 
 1,25 
 
 2.25 
 
 10.8 
 
 3.00 
 
 14.3 
 
 1.50 
 
 2.69 
 
 12.9 
 
 3.63 
 
 17.4 
 
 2.0 
 
 3.66 
 
 17.5 
 
 5.02 
 
 24.0 
 
 2.50 
 
 5.77 
 
 27.6 
 
 7.67 
 
 36.7 
 
 3.0 
 
 7.54 
 
 36.0 
 
 10.25 
 
 49.0 
 
 3.50 
 
 9.05 
 
 43.3 
 
 12.47 
 
 60.0 
 
 4.0 
 
 10.72 
 
 51.0 
 
 14.97 
 
 72.0 
 
 4.50 
 
 12.49 
 
 60.0 
 
 18.22 
 
 87.0 
 
 5.0 
 
 14.56 
 
 70.0 
 
 20.54 
 
 98.0 
 
 6.0 
 
 18.76 
 
 90.0 
 
 28.58 
 
 137.0 
 
 7.0 
 
 23.41 
 
 112.0 
 
 37.67 
 
 180.0 
 
 8.0 
 
 25.00 
 
 120.0 
 
 43.00 
 
 206.0 
 
 8.0 
 
 28.34 
 
 136.0 
 
 
 
 9.0 
 
 33.70 
 
 161.0 
 
 48.73 
 
 233.0 
 
 10.0 
 
 32 00 
 
 153 
 
 
 
 10.0 
 
 35.00 
 
 167.0 
 
 
 
 10.0 
 
 40.00 
 
 191.0 
 
 "54^74 
 
 "262.Q 
 
 11.0 
 
 45.00 
 
 215.0 
 
 60.08 
 
 287.0 
 
 12 
 
 45 00 
 
 215 
 
 
 
 12.0 
 
 49.00 
 
 234.0 
 
 65.42 
 
 313.0 
 
APPENDIX 
 
 199 
 
 TABLE 6D 
 A. G. I. Standard Gas 
 
 Nominal inside 
 diameter (inches) 
 
 Weight pounds 
 per foot 
 
 Current for 1 mv. 
 on 1 ft. (amperes) 
 
 4 
 
 17.3 
 
 14.1 
 
 6 
 
 27.3 
 
 22.2 
 
 8 
 
 38.0 
 
 30.9 
 
 10 
 
 51. 0* 
 
 41.5 
 
 12 
 
 67.0 
 
 55.0 
 
 16 
 
 102.0 
 
 83.0 
 
 20 
 
 139.0 
 
 113.0 
 
 24 
 
 186.0 
 
 152.0 
 
 30 
 
 256.0 
 
 209.0 
 
 36 
 
 346.0 
 
 282.0 
 
 42 
 
 453.0 
 
 369.0 
 
 48 
 
 610.0 
 
 405.0 
 
 TABLE 6E 
 LEAD PIPE 
 
 
 
 
 Current for 
 
 Specimen No. 
 
 Card diameter 
 (inches) 
 
 Card weight 
 (Ibs. per ft.) 
 
 1 mv. drop per 
 ^foot (amperes) 
 
 1 
 
 0.25 
 
 0.5 
 
 0.915 
 
 2 
 
 .25 
 
 .5 
 
 .908 
 
 3 
 
 .25 
 
 .5 
 
 .942 
 
 4 
 
 .75(AA) 
 
 3.5 
 
 7.257 
 
 5 
 
 .75(AA) 
 
 3.5 
 
 7.332 
 
 6 
 
 .75(AA) 
 
 3.5 
 
 7.305 
 
 7 
 
 .75(AA) 
 
 3.5 
 
 7.123 
 
 8 
 
 .75(AA) 
 
 3.5 
 
 7.148 
 
 9 
 
 .75(AA) 
 
 3.5 
 
 7.067 
 
 10 
 
 .00(C) 
 
 2.5 
 
 4.914 
 
 11 
 
 .00(C) 
 
 2.5 
 
 4.921 
 
 12 
 
 .00(C) 
 
 2.5 
 
 4.958 
 
 13 
 
 .00 (A A) 
 
 4.75 
 
 9.785 
 
 14 
 
 .OO(AA) 
 
 4.75 
 
 9.833 
 
 15 
 
 .OO(AA) 
 
 4.75 
 
 9.766 
 
 16 
 
 2.00(C) 
 
 6.0 
 
 11.81 
 
 17 
 
 2.00(C) 
 
 6.0 
 
 11.78 
 
 18 
 
 2.00(C) 
 
 6.0 
 
 11.77 
 
 19 
 
 2.00(AA) 
 
 9.0 
 
 18.14 
 
 20 
 
 2.00(AA) 
 
 9.0 
 
 18.11 
 
 21 
 
 2.00(AA) 
 
 9.0 
 
 18.11 
 
 22 
 
 .25 
 
 .5 
 
 .915 
 
 23 
 
 .25 
 
 .5 
 
 .913 
 
 24 
 
 .25 
 
 .5 
 
 .915 
 
 25 
 
 .75(C) 
 
 1.75 
 
 3.302 
 
 26 
 
 75(C) 
 
 1.75 
 
 3.343 
 
 27 
 
 .75(C) 
 
 1.75 
 
 3.322 
 
200 
 
 APPENDIX 
 
 IDtlQ 
 
 papuoq 
 
 Q 
 
 V 
 
 c/j 
 
 uo 
 
 jo 
 
 UOI4D3JIQ 
 
 ti 
 o 
 
APPENDIX 
 
 201 
 
 2 
 
 * 
 
 *a 
 
 c 
 
 V 
 
 1 
 
 8 
 
 .s 
 
 B 
 c 
 
 5 
 
 i 
 
 rt 
 
 .2 
 
 H 
 
 CURRENT MEASUREMENTS 
 
 DIREC- 
 TION 
 
 
 
 
 
 ! 
 
 a 
 
 O 
 
 < 
 c 
 
 is 
 
 
 
 
 
 
 
 
 
 
 
 
 K 
 
 i 
 
 
 
 
 
 
 
 ' 
 
 Drop Millivolts 
 
 I 
 
 ::::::::::: 
 
 
 
 
 
 
 
 
 
 
 1 
 
 : : :::::::: 
 
 
 
 
 
 
 
 
 
 
 
 
 if 
 
 ::::::::::: 
 
 
 
 
 
 
 ::::::::: 
 
 ^ 
 
 
 1^1 
 
 | 
 
 ::::::::: 
 
 
 
 
 
 
 
 
 
 
 .a'B.ll 
 
 
 
 
 
 
 R<i 
 
 O-I^S 
 
 
 
 
 
 
 
 :::::::::::: 
 
 
 
 
 
 
 
 ;. ; ; ! ; i '. '. 
 
 
 i i i ; i ; i-; i i i 
 
 
 
 : : : 
 
 
 
 
 
 
 
 
 III 
 
 
 
 
 
 
 
 . 
 
 
 
202 
 
 APPENDIX 
 
 POTENTIAL MEASUREMENTS 
 
 II- 
 
APPENDIX 
 
 203 
 
 u 
 
 Volts 
 ties Refer 
 to (A) 
 
 
 i 
 
 
 
 
 
 
 i 
 
 i 
 
 
 
 
 
 
 
 if 
 
 c 
 
 i 
 
 
 
 
 
 
 
 
 d 
 
 
 
 
 
 
 
 
 s 
 
 
 
 
 
 
 J. 
 
 
 OJ 
 
 
 
 
 
 
 I 
 
 
 1 
 
 
 
 
 
 
 
 
 i 
 
 C 
 
 2 
 
 
 
 
 
 
 
 Q i 
 
 
 
 
 
 
 
 
 
 d 
 
 
 
 
 
 
 
 
 s 
 
 
 
 
 
 
 
 jlilJ 
 
 
 
 
 
 
 1 
 
 3 "S 8 '' 
 
 
 
 
 
 
 
 Q ^ ** B 
 
 
 
 
 
 
 Q 
 
 liili 
 
 
 . 
 
 ; 
 
 
 
 
 I1M 
 
 
 
 
 
 
 c 
 
 
 
 
 
 
 
 .2 
 
 
 
 
 
 
 
 ! 
 
 
 
 
 
 
 
 j 
 
 
 
 
 
 
 j. 
 
 
 
 
 
 
 
 
 
 5 
 
 1 
 
 
 
 
 
 
204 
 
 APPENDIX 
 
 1 1 
 
 ! -a 
 I *s 
 
 &, 
 
 III 
 
 II 
 
Engineering 
 Library 
 
 
 xv- % 
 
 UNIVERSITY OF CA1LIFQIWIA LIBRARY