UNIVERSITY OF CALIFORNIA AT LOS ANGELES MODERN Electrical Construction A RELIABLE, PRACTICAL GUIDE FOR THE BEGINNER IN ELECTRICAL CONSTRUCTION SHOWING THE LATEST APPROVED METHODS OF INSTALLING WORK OF ALL KINDS AC- CORDING TO THE SAFETY RULES OF THE National Board of Fire Underwriters By HENRY C. HORSTMANN VICTOR H. TOUSLEY Authors of "Modern Wiring Diagrams and Descriptions' 3flllu0tratrD CHICAGO FREDERICK]. DRAKE & CO., PUBLISHERS 1905 COPYRIGHT, 1904 BY HORSTMANN AND TOUSLEY TK PREFACE In this volume an attempt is made to provide the beginner in electrical construction work with a reliable, practical guide ; one that is to tell him exactly how to install his work in ac- .y cordance with the latest approved methods. It is also intended to give such an elaboration of "safety rules" as shall make the book valuable to the finished work- - man as well. To this end the rules of the "National Electrical g Code" of the National Board of Fire Underwriters have been U given in full, and used as a text in connection with which there is interspersed in the proper places a complete explana- ^f tion of such work as the rules may apply to. This method of teaching and explaining practical electricity may at first glance seem somewhat haphazard, but it resembles very closely the -factual method by which the most successful, practical work- W men have learned' the trade. It is thought that explanations pertaining directly to the work in hand will be more deeply considered and more likely to be fully comprehended than explanations necessarily more abstract. It should be noted that, while the rules published in the "National Electrical Code" are standard and work done in conformity with them will be first-class, several of the larger cities have ordinances governing electrical work which con- flict in some details with these rules. Workers in such cities should, therefore, provide themselves with copies of these ordinances (usually obtainable without charge), and compare them with the rules given in this work. It is necessary for the electrical worker at all times to keep himself posted, for safety rules are liable to change. The tables concerning screws, nails, number of wires that can be used in conduit, etc., are especially prepared for this volume, and give to it particular value for practical men. THE AUTHORS. CHAPTER I. The Electric Current. It is quite customary and convenient to speak of that agency by which electrical phenomena, such as heat, light, magnetism, and chemical action are produced as the electric current. In many ways this current is quite analogous to cur- rents of air or water. Just as water tends to flow from a higher to a lower level, and air from a region of greater density or pressure to one of lesser density, so do currents of electricity flow from a region of high pressure to one of low pressure. Currents of electricity form no exception whatever to the general law of all action, which is along the lines of least resistance. It must not be understood, however, that electricity actually flows in or along a conductor, as water does in a pipe, and the analogy must not be carried too far, for the flow of water in pipes is influenced by many conditions which do not influence a flow of electricity at all, and vice versa ; there are conditions surrounding conductors, which influence the flow of electricity which do not affect the flow of water. Above all, let it be understood that electricity is not inde- pendent energy, any more than the belt which gives motion to a pulley is. In other words, it is not a prime mover, it is simply a medium which may be used for the transmission of energy, just as the belt is used. To use electricity as a medium for the transmission of energy, it must be, we may say, compressed, or, to use a more properly technical expres- sion, a difference of potential or pressure must be created in a system of conductors. This is very similar to the use of air 8 MODERN ELECTRICAL CONSTRUCTION. for power transmission ; this must also be compressed so that a difference of pressure exists within a system of piping. It is the flow of electricity or air which takes place when switches or valves are operated and which tends to equalize this pressure, i. e., flow from high to lo// pressure, that does our work. The real energy, however, (so far as we are con- cerned), to which we must look for our initial motion in either case is derived from the coal which generates steam; or, in the case of water-driven machinery, the rays of the sun which evaporate water, allowing it to be carried to higher levels, from whence it flows downward over dams ar.d falls on its way back to the lowest level. In the battery, the real energy is that of chemical action, which is transformed into electrical energy. The flow of current can take place only in a system of conductors which usually, for convenience, are made in the form of wires. The current for practical purposes may be considered as flowing along such wires only. It is not, how- Figure 1 ever, necessary that these wires should be of any particular size, or consist all of the same material. In an electric bat- tery, part of the circuit consists of the liquid contained within the battery; the rest being made up usually of wire. In an incandescent light circuit part of the circuit consists of the ELECTRIC CURRENT. 9 lamp filament (usually carbon), while the balance of the cir- cuit consists of copper wire. The flow of current is also said to have a certain direction ; that is, it is noticed that many of its effects are reversed when the terminals of the battery are reversed. Referring to Fig. 1, which shows a battery of three cells, the current flows from the copper element at bottom of jar 1, along the wire to the zinc element at top of jar 2, thence through the liquid to the copper element at bottom of jar 2, and from there to the zinc at top of jar 3, etc., and finally through the wire a back to the starting point. Within the battery the current flows from the zinc to the copper and the decomposition of the zinc gen- erates the current. In the wire outside of the battery the cur- rent flows from the copper to the zinc as indicated by arrows. The combination of battery and wire is known as an electric circuit. The current will flow in this circuit only while it is complete, that is while each wire connects to its proper place as shown. If any wire is disconnected, the current flow v.ill cease. Such a circuit is said to be open, but when all connections are properly made it is said to be closed. Work can be obtained from a flow of current in many ways. If the current be forced to flow over a wire which is very small in proportion to the current carried, it will be heated thereby and finally melted if the current is excessive. This is how electric light is obtained. If a wire carrying current be wound many times about an iron bar this bar becomes a magnet ; that is, while the cur- rent is flowing around it, the bar has the power to attract other objects of iron or steel. The bar if made of well an- nealed iron will be a magnet while current is flowing around it, but will cease to be magnetic whenever the current flow ceases. Upon this fact the operation of electric bells, telegraph instruments and motors is based. If a current of electricity flow through a properly arranged 10 MODERN ELECTRICAL CONSTRUCTION. "bath," one of the plates will be gradually consumed and the other increased in weight. This effect is made use of in electro-plating, etc. If the jar contains water slightly acid- ulated and the current flows through it, the water will be decomposed and oxygen and hydrogen gas will be formed. This and many kindred effects are daily used in thousands of chemical laboratories. If a wire carrying an electric current be placed very close to another wire forming a closed circuit, a wave of current will be induced in that wire every time the current in the other is made or broken, i. e., whenever it starts to flow or stops flowing. This fact forms the basis of the alternating current transformer. All of these facts are used sometimes together, sometimes sir.gly in measuring the electric current. Conductors and Insulators. Electrically speaking, all substances are divided into two classes. They are either conductors or insulators. By thi* is not meant that some substances can carry no current at all, for, as a matter of fact, there is no such thing as either a perfect conductor or a pecfect insulator. A current of elec- tricity can be forced through any substance, provided the pres- sure (E. M. F.) be made great enough, and there is no easier path open to the current. The two terms, conductor and insulator, are relative terms and must be understood simply to mean that the electrical resistance of a good conductor is infinitesimally small as compared to that of a good insulator. The lower the specific resistance of any substance, the better its conducting qualities; the higher the specific resistance of any substance, the better will be its insulating qualities. At the left is given a list of good conductors, in the order of their conductivity, the figures representing the relative con- ELECTRO- MOTIVE-FORCE. 11 ductivity of these metals. A list of insulators is given at the right; all of these are more or. less affected by moisture, los- ing their insulating qualities when wet. Silver 100.0 Dry air. Copper 94.0 Rubber. Gold 73.0 Paraffin. "Platinum 16.6 Slate. Iron 15.5 Marble. Tin 11.4 Glass. Lead 7.6 Porcelain. Bismuth .. ,1.1 Mica. Fiber. Wood. Shellac. Pressure or Electro-Motive Force. Currents of electricity flow only in obedience to electrical pressure. This pressure is measured and expressed in volts, the unit of electrical pressure being the volt. If we speak of water or steam pressure, we speak of it in pounds, the pound being the unit of measurement. In speaking of elec- trical pressure we refer to it as of so many volts. There is no direct connection between the pound and the volt, but each in its place means about the same thing. The volt is defined as that difference of potential (pres- sure) that must be maintained to force a current of one ampere through a resistance of one ohm. If we have a resistance greater than one ohm and wish to send a current of one ampere through it, we can do so by increasing the pressure or voltage, as it is termed, accordingly. The current flowing in a circuit can also be reduced by reduc- ing the voltage. The ordinary incandescent lamps operate at about 110 volts pressure, although some are built for 220 volts. An elec- tric bell requires about 2*/ 2 volts (a battery of 2 cells) for proper operation. 12 MODERN ELECTRICAL CONSTRUCTION. Resistance. We have seen that a flow of current always takes place along or in a conductor. Every conductor, no matter how large or small it may be, offers some resistance to this (low of current just as the water pipe offers more or less resistance to the flow of water. This resistance may be measured and expressed in ohms; the unit of electrical resistance being the ohm. The ohm is defined as that resistance which requires a difference of potential of one volt to send a current of one ampere through it. If we should desire to send a greater cur- rent through any resistance, we can do so by increasing the pressure, just as we can increase the flow of water in a pipe by increasing the pressure or head of water in the tank that supplies it. If the pressure is fixed we can decrease the current by using a wire of greater resistance or increase it by using wires of lesser resistance. The ohm is the resistance of a column of mercury 106.2 centimeters long (about Z l /2 feet) and one square millimetre (about .0015 sq. in.), in cross-section, at the temperature of melting ice. The resistance of a No. 14 copper wire about 380 feet long is equal to one ohm. The resistance of all conductors increases directly as the \ Figure 2 length and decreases as the cross-section increases. In Figure 2 the resistance of the two bars of copper is exactly equal. Bar No. 1 having a cross-section of 4 square inches and being 4 feet long, while bar No. 2 has a cross-section of only 1 square inch and is only one foot long. If bar No. 1 were OHMS LAW. 13 reduced to a cross-section of 1 square inch, it would become 16 feet long and would have a resistance 16 times as great as that of bar No. 2. Current. The electric current is the result of electrical pressure (volts) acting through a resistance, and is measured in amperes, the ampere being the unit of current strength. The ampere is defined as that current which will flow through a resistance of one ohm when a difference of potential or pres- sure of one volt is maintained at its terminals. The ampere expresses only the rate of flow, not the quan- tity. Knowing the amperes if we would know the quantity, we must multiply by the time that the rate of flow continues. 1 he rate of flow is analogous to the speed of a train ; unless we know how long the train is to maintain a certain speed, we have no idea how far it is going. Quantity in electricity is measured in coulombs. The coulomb is the quantity of current delivered by a flow of one ampere in one second. Ohm's Law. Ohm's law expresses the relation of the three principal electrical units to each other and forms the basis of all elec- trical calculations. This law states that in any electric circuit (with direct current) the current equals the electro-motive force divided by the resistance. The current, we have already seen, is the medium which does our work. Current flow, we see from this law, can be increased either by increasing the electro-motive force, or electric pressure, which causes the flow ; or by decreasing the resistance which tends to prevent current flow. Expressed in symbols it is this : I^E/R ; where I stands for 14 MODERN ELECTRICAL CONSTRUCTION. current, E, for electro-motive force, and R for resistance. If, as an example, we have an electro-motive force (which we shall henceforth designate by the customary abbreviation, E. M. F.) of 110 volts and a resistance of 220 ohms, the resulting current will be 110 divided by 22Q= l / 2 ampere, being approxi- mately the current used in a 16 cp. incandescent lamp at 110 volts. Thus it will be seen that by a very simple calculation we can find the current flow in any conductor if we but know the E. M. F. and the resistance of that circuit. This formula can also be used to find the E. M. F., if we know the value of current and the resistance, since E divided by R=I ; I times R must equal E. If the current and resist- ance are known, we need only to multiply them together to find the E. M. F.; IXR=E. Knowing the current and E. M. F., we can find the value of the resistance by dividing the E. M. F. by the current ; E/I=R. As a practical application of these formulas : If we wish to know how much current a certain E. M. F. can force through a certain resistance, we must divide the E. M. F. (volts) by the resistance (ohms.) If we wish to know what E. M. F. (volts) will be necessary to force a certain cur- rent (amperes) through a certain resistance, we need only multiply the current (amperes) to be obtained by the resist- ance in ohms. If we wish to know how much resistance (ohms) must be placed in a circuit to keep down the current flow to a certain limit, we need only divide the E. M. F. (volts) by the desired current (amperes) ; the result will be the value in ohms of the required resistance. Power. The power consumed or transmitted in an electric cir- cuit equals the product of the volts and amperes; pressure and current. POWER. 15 To find the power of a steam engine, we must know the pressure of the steam and the quantity used ; the power con- tained in the water of a dam depends upon its volume and its head. The power we can obtain from the wind depends upon its speed and the surface we expose to it which also measures the quantity. All of these cases are analogous and similar. Power ex- presses the rate of doing work, thus the rate of work is the same whether we are lifting one pound at the rate of 100 feet per minute, or 100 pounds at the rate of one foot per minute. The unit of electrical power is the watt. It is the power expended in an electric circuit when one ampere flows through a resistance 9f one ohm, or when a difference of potential of one volt is maintained in a circuit having a resist- ance of one ohm. In an electric light circuit, for instance, as far as the power is concerned, it is immaterial whether each lamp requires 110 volts and l /z ampere, or 55 volts and one ampere, or 220 volts and % ampere. The power (watts) expended in an electric circuit is always equal to the volts multiplied by the amperes; thus, one ampere at 1,000 volts is equal to 100 amperes at 10 volts, or to 200 amperes at 5 volts. In any power transmission whenever the pressure (volts) is lowered, the current (amperes) must be increased or the power (watts) will fall off, and, on the other hand, whenever the pressure is increased the current may be decreased. Instead of multiplying volts by amperes, we can find the power in an electric light circuit by multiplying the current by itself and then by the resistance ; or the E. M. F. by itself and divide by the resistance. Thus knowing the volts and the amperes, we use the . formula E X I=W. Knowing only the amperes and the ohms, we may use the formula, I 2 X R = W ; and lastly, 16 MODERN ELECTRICAL CONSTRUCTION. knowing only the volts and ohms, we use the formula, . In the above E stands for E. M. R, or volts; I for current or amperes; and R for resistance or ohms. _ Divided Circuits. Currents of electricity always flow along the paths of least resistance just as currents of water do. Water, it is well known, will not flow over the top of a mill dam while ii Figure 3 there is an opening alongside of it through which it can flow. If a barrel of water be provided with two openings, one large opening and one small, a much larger quantity will flow out through the. large opening than through the small. This is because the resistance to the flow of water of the large opening is so much less than the resistance of the small opening. An electric current will act in just the same way; the conductor having the lesser resistance will carry the greater current. If we know the resistances of the different paths open to a certain current we can determine to a nicety how much current will flow in each. In Figure 3, which repre- sents diagramatically a battery of two cells and an electric circuit, the resistance of the two paths, a and b, is equal to DIVIDED CIRCUITS. 17 10 ohms each, and the current will divide equally between them. If the resistance of a were 5 ohms, and that of b, 10 ohms, two-thirds of the total current would pass through a and the one-third through b. In all such divided circuits, the current is always in- versely proportional to the resistance and the simplest way > find the current in each is to add the resistances of the two circuits; for instance . as above, 5 plus 10 equals 15; now 15 of this current will flow through the 10 ohms and 10/15 of the current will flow through the 5 ohms. To determine the combined resistance of the two wires a and b, we need simply to consider them as made into one wire. If they are both alike, they would, if made into one wire, be twice as large as either one is at present, and would then have only one-half as much resistance as either one had before; for the resistance of any conductor increases directly as its length, and decreases as the cross-section increases Hie combined resistances of any two conductors can be found by multiplying their two resistances together and dividing this product by their sum. Thus, again taking the value of a and b as 10 ohms each, 10X10 equals 100, this divided 10 plus 10 equals 5, which is the combined resistance of the two. If we have a large number of branch circuits as shown in Figure 4, which represents diagramatically an incandescent Figure 4 electric light circuit of 12 lights (which is equal to 12 separate :ircuits, since each lamp really forms a circuit by itself), we can find the joint resistance of the 12 by proceeding as before; t is, multiplying together the resistance of the first and 18 MODERN ELECTRICAL CONSTRUCTION. second lamp and dividing by the sum of these resistances ; next take the result so obtained (which is the combined resist- ance of the first two lamps) and with it multiply the resist- ance of the third lamp and divide by the sum as before. By repeating this operation and always treating the joint resist- ances already found as one circuit, the joint resistance of any number of such circuits can be found. Another and a very much quicker way consists in using the following formula : The joint resistance of any number of parallel circuits is equal to the reciprocal of the sum of the reciprocals. The reciprocal of any number is 1 divided by that number. If we have three circuits, having respectively 10, 20, and 30 ohms resistance, we proceed in the following way: The reciprocal of 10 is 1/10, of 20, 1/20, etc., the joint resistance, there- fore, is 1/10 plus 1/20 plus 1/30 equals 11/60, and 1 divided by this number which is 5 5/11. These methods are only necessary when the resistances are of different values. When all of them are alike, as is usual with incandescent lights, the resistance of one lamp needs only to be divided by the number of lamps to find the joint resistance. Thus, supposing each of the 12 lamps to have a resistance of 220 ohms, the joint resistance of the circuit would be 220/12=181/3. CHAPTER II. Electric Bells. We are now in a position to apply the electrical laws we have just discussed practically, and for this purpose may take up electric bells and bell circuits. Figure 5 shows an electric bell, push button and battery, all connected up and complete. The action of the bell when Figure 5 fully connected is as follows: Pressing the push button closes the circuit and current at once flows from the carbon pole marked + through the push button to the binding post A on the bell frame, thence along the fine wire W to the iron frame-work supporting the armature, B. This frame- 20 MODERN ELECTRICAL CONSTRUCTION. work is in electrical connection with B. The armature, B, is provided with contact spring S, which normally rests against the adjusting screw, C. The current now passes from the contact spring to the adjusting screw and from it to the wire wound on the magnets, M, around the many turns of wire to the binding post, D, and back to the zinc pole of the battery marked . The current circulating many times in the wire wound on the spools of M makes the iron cores magnetic so that they now attract the armature B. When this armature is at- tracted, it moves towards the magnets, M, and carries the small contact spring with it, thus breaking the connection be- tween C and S. This stops the current flow and the magnets, M, are at once demagnetized, thus releasing the armature B, which flies back and again clores the circuit at CS, this causes the armature to be attracted again and once more the circuit is broken. In this way the armature is made to strike the gong continuously while the circuit is kept closed at the push button. When the button is released, the circuit is permanently open and the bell at rest. In the figure there is shown only one cell, this, if a good form is selected, is sufficient for a new bell if the circuit is not long. When, however, the bell is used much the contact points are eaten away by the little sparks occurring every time the bell breaks the circuit. Dirt is also likely to gather on them and prevent good contact being made. Both of these factors add resistance to the circuit, and consequently lessen the current flow. We have seen before that the current equals the E. M. F. divided by the resistance, and in order to obtain the necessary current flow to operate the bell, we may either clean the contact points to lessen the resistance, or increase the E. M. F. by adding another cell in series with the first. ELECTRIC BELLS. 21 The latter expedient is by far the better, because it gives us a little surplus of power which is very useful to over- come variations in adjustment of the contact spring, loose contacts, dirt, etc. We should avoid using too many cells as well as not enough. If too many cells are used, there Or n Or n ,777 Figure 6 will be much unnecessary damage done to contact points by the larger sparks. If the circuit is very long, the great length of wire will also provide additional resistance. This can be overcome in two ways, by increasing the E. M. F. as above, or by using larger wires. We have already seen that the larger the wire, the less will be its resistance. It is common practice to use 22 MODERN ELECTRICAL CONSTRUCTION. No. 18 copper wire for all ordinary distances and for single bells. With large bell systems, it is customary to use No. 16 or 14 for the main wire, which leads to all of the bells and may be called upon to supply several bells at the same time. Figure 6 shows a diagram of such a system and in case the three push buttons are used at the same time, three times as much current will flow in the main or battery wire a as in either of the other wires. We have seen before that currents of electricity divide among different circuits in the inverse ratio of their resist- ances. In other words, the circuit having the least resistance will carry the most current. If our bell system, Figure 6, be "grounded" at the two points x and y (i. e., bare wire in contact with metal parts of buildings which are connected together) the current instead of flowing through the longer circuit and the bell, will flow through the short circuit and leave it impossible to operate the bells. If the contacts, at x and y are poor, i. e., of high resistance, only a small part of the current will leak from one to the other. In such a case, the bells may work properly, but the battery will soon run down and there is a strong likelihood that one of the wires will be eaten away through electrolytic action. To prevent troubles of this kind, bell wires should be well in- sulated and kept away from pipes or metal parts of building. Damp places should also be avoided and special care is recommended for the battery wire a, Figure 6. For further information concerning diagrams, etc., of bell circuits the reader is referred to Wiring Diagrams and Descriptions by the authors of this work, Fred J. Drake & Co., Chicago. Bell wires are usually run along base boards, over picture mouldings, etc., in some cases they are also fished as explained further on. Batteries should be located in cool, dry places, where they are not liable to freeze, and where they are readily accessible as they must be kept nearly full of water and must be recharged from time to time. 23 The Telephone. The principle and action of the Bell telephone can be best explained by reference to Figure 7. In this figure, A repre- sents the transmitter, and B, the receiver. The essential parts of the transmitter are: the diaphragm, a; an electric circuit, containing a battery, b, and consisting of the wires, c, c 1 and partly wound upon an iron core, d. This electric circuit, it will be seen from the figure, con- nects with one pole to the diaphragm, a, and with the other to a small metal plate, e. Between the diaphragm, a (which is a plate of very thin iron), and the plate, c, there are many small pieces of carbon which complete the circuit. When now a party speaks into the mouthpiece of the transmitter, Figure 7 the sound waves cause the diaphragm, a, to vibrate; the rate of vibration and character of the vibrations being an exact duplication of the voice speaking into it. These vibrations cause the small pieces of carbon between the diaphragm and the back plate to be alternately compressed and allowed to expand. Now the resistance of these carbon pieces is de- creased as they are tightly pressed together, and again in- creased when the pressure is released. Therefore the cur- rent of electricity flowing through them varies continuously while the diaphragm is in motion. This varying current circulates around the lower part of the iron core, d, and the two windings upon it form an 24 MODERN ELECTRICAL CONSTRUCTION. ordinary induction coil. Every variation of current strength in the circuit of the transmitter is by means of it reproduced in the circuit of the receiver, B. The essential parts of the telephone receiver are: The diaphragm f, very similar to that of the transmitter, the two magnets, g, and the electric circuit coming from the induction coil of the transmitter. The electric circuit, we have already seen, is traversed by electric currents exactly like those that flow in the circuit of the transmitter. These currents pass around electro-magnets, g, and attract the diaphragm, /, more or less strongly in proportion to the varying degrees of current strength. In this manner the diaphragm, /, of the receiver is made to vibrate in exact unison with that of the transmitter, and thus to reproduce exactly the sounds given to the trans- mitter. The transmitter is not absolutely necessary for the re- Figure 8 ceiver can be used as such, and in fact was so used at first. Lines of short distances can be operated without transmit- ters, but the speech will not be as plain. INDUCTION COIL. 25 Figure 8 is a diagram of the connections of two telephone instruments together with the necessary call bells. When the lines are not in use, the receivers, a, are hanging on the hooks, h, holding them down as shown by dotted lines. This leaves the circuit complete through the earth, g, magneto generator, e, bell f, line i, and duplicates of these parts at the right. When now the magneto generator is operated both bells will ring. When the receivers are removed, a spring forces the hook upwards making the connection shown in solid lines. This closes the battery circuit which must be open when the instrument is not in use or the battery will run down. The talking circuit is now complete from earth, g, through the receiver, a, induction coil, b, line i, and duplicates of these parts at the right. The Induction Coil. Figure 9 is a diagramatic illustration of an induction coil as used mostly by medical men. Such an instrument Figure 9 consists of an iron core, B, usually made up of a number of soft iron wires; and two electrical circuits insulated from each other, and terminating in the two pair of binding posts, A and D. Of these two circuits A consists of a short length 26 MODERN ELECTRICAL CONSTRUCTION. of comparatively heavy wire wound upon the iron core, and is known as the primary coil. D is a similar coil, but usually consisting of many more turns of wire, and the wire is also of much smaller gauge and is known as the secondary coil. The operation is as follows : A battery is connected to the binding posts, A, and current begins to flow in the circuit. In this circuit is an interrupter or vibrator, E, constructed similarly to the one described in connection with the electric bell. As current flows through the primary coil, it mag- netizes the core, B, and this attracts the armature, E, causing it to break the connection between itself and the adjusting screw. As this connection is broken, the current in A ceases to flow, the core is de-magnetized and the armature again connects with the adjusting screw. This action is repeated just as in the electric bell, and in consequence the core B, is rapidly magnetized and de-magnetized. . Every time the core, B, is magnetized a current of electric- ity, lasting, however, only an instant, is induced in the second- ary coil, D. The magnetism in the core is caused by a cur- rent of electricity circulating around it, and currents of electricity are in turn produced by this magnetism in the other or secondary coil. This method of producing electric currents is known as electro-magnetic induction, and currents so produced are said to be "induced" currents, hence the name induction coil. The currents so induced are alternating, that is, changing in direction. At the "making" of the primary circuit, the cur- rent in the secondary coil is in a direction which opposes the magnetization of the core by the primary current; at the time of "break" in the primary circuit, the induced current will be in the opposite direction. The tube, C, is movable and may be slipped entirely in over the iron core, or withdrawn. entirely. If it is in, the currents which were before being induced in the secondary wires are BATTERIES 27 now induced in the metal of the tube and consequently the effect on the secondaries is very much reduced. The energy in the primary and secondary coils is always equal. If the two coils have the same number of turns, the currents and electro-motive forces are exactly alike. If the secondary coil has more turns of wire than the primary, the induced E. M. F. in it will be greater, but the current will be smaller and vice versa. The induction coil is very similar to the alternating current transformer, the main difference being that the transformer does not have an in- terrupter since the current supplied to it is itself constantly alternating. Batteries. Currents of electricity for commercial purposes are pro- duced either by dynamo electric machines or by batteries. A "battery" is the name given to a number of cells con- nected together so as to produce a current greater than one Figure 10 Figure 11 cell alone could produce. Figure 10 shows one cell of a kind that is generally used only intermittently, as for instance with door-bells. When the bell is not ringing the battery is idle. 28 MODERN ELECTRICAL CONSTRUCTION. This style of cell is very useful for such work, but entirely useless for work requiring current continuously. The cell consists of a glass jar which is filled about Y* full of water in which a quantity of sal-ammoniac is dissolved. Immersed in this solution is a carbon cup or center, which forms the positive or + pole of the cell, and a zinc rod, carefully separated from the carbon by a rubber washer at the bottom and a porcelain tube at the top. So arranged, the current tends to flow, in the battery, from the zinc to the carbon and if the zinc and carbon outside of the cell be joined by a piece of wire or other conductor of electricity, the current will flow in the external circuit, from the carbon back to the zinc. If the zinc and carbon are not joined by a conductor of electric- ity there will be no current flow, but merely an electrical pres- sure tending to send a current. Each cell of this kind has an electro-motive force of about 1.4 volts. This is not suffic- ient for general use in connection with bells, etc., and in order to obtain greater current strength a number of cells are connected together in series as shown in Figure 11. This figure shows a different kind of cell, but will never- theless illustrate the method of connecting cells in series; which is, to connect the carbon or copper pole of the first cell to the zinc of the second, and again the carbon pole of the second to the zinc of the third, continuing in this way through all of the cells. Thus connected, all of the electro-motive forces act in one direction and if we have twelve cells each of an electro-motive force of 1.4 volts, we obtain a total electro-motive force to apply on our work of 12 X 1.4 or 16.8 volts. Should we, however, connect six of the twelve cells as above, and then accidentally connect the other six in the opposite direction, that is, the zinc of the sixth cell to the zinc of the seventh, and then continue in this order, we should obtain no current whatever; six of our cells would tend to BATTERIES. 29 send current in one direction and six in the other, so that the result would be nothing. Should ten cells be properly con- nected to send current in one direction and two connected to oppose them, the net electro-motive force would be 10 X 1.4 minus 2 X 1.4, which is 11.2. The ten cells would force current through the other two in the opposite direction. The electro-motive force of a cell is independent of its size, that is, a very small cell would set up just as high an electrical pressure as a very large one made of the same material. A large cell is, however, capable of delivering a much stronger current because its own resistance to the cur- rent flow is much less than that of a small cell. Large cells will, therefore, in most cases give very much better service than small ones. Especially in cases where considerable current is required as in electric gas-lighting and annunciator work, where it is always possible that two or three bells or fixtures may be called into action at the same time. In setting up and maintaining sal-ammoniac batteries, the following general rules should be observed : Use only as much sal-ammoniac as will readily be dis- solved; if any settles at the bottom it shows that too much has been used. Keep your battery in a cool place, but do not allow it to freeze. See that the jars are always about M full of water. Keep the tops of glass jars covered with paraffir to prevent salts from creeping. The battery should never be allowed to remain in action (i. e., send current) continuously, or it will run down. If it has been run down through a short circuit or other cause, it should be left in open circuit for several hours ; it will then usually "pick up" again. The so-called dry-batteries are made up of about the same material, but applied in form of a paste. They are 30 MODERN ELECTRICAL CONSTRUCTION. suitable for the same kind of work and especially handy for portable use. For continuous current work, such as telegraphy, for instance, the kind of battery shown in Figure 11 is generally used. The electro-motive force of this style of battery is a little less than that of the sal-ammoniac battery and its re- sistance is considerably greater. Therefore, it is not well adapted for work requiring con- siderable current strength. Bells, telegraph instruments, etc., to be used with this battery require to be specially designed for it; the current being less in quantity must be made to circulate around the magnets many jnore times in order to fully magnetize them. The sal-ammoniac batteries cannot be used continually or they will run down ; this battery must be kept at work always or it will deteriorate. This style of cell is known as the crow-foot or gravity cell, the action of gravity being depended upon to separate the essential elements of the solution. To set up this battery, the zinc crow-foot is suspended from the top of the glass jar as shown. The other element of the cell consists of copper strips riveted together and connected to a rubber-covered wire shown at the left of each cell, Figure 11. This copper is spread out on the bottom of the jar and clear water poured in until it covers the zinc. Next drop in small lumps of blue vitriol, about six or eight ounces to each cell. The resistance may be reduced and the battery be made immediately available by drawing about half a pint of the upper solution from a battery already in use and pouring it intq the jar; or, when this cannot be done, by putting into the liquid four or five ounces of pulverized sulphate of zinc. Blue vitriol should be dropped into the jar as it is con- sumed, care being taken that it goes to the bottom. The BATTERIES. 31 need of the blue vitriol is shown by the fading of the blue color, which should be kept as high as the top of the copper, but should never reach the zinc. A battery of this kind when newly set up should be short circuited for a few hours, that is, a wire should be con- nected from the zinc at one end of the battery to the copper at the other. There are many styles of batteries and different chemicals are used with them. The two kinds above described are, however, the most used. The methods of connecting is in all batteries the same. Figure 12 shows a diagram of a battery connected in series; the long thin lines repre- sent the copper or carbon pole from which the current flows in the external circuit and the short thick lines represent the zinc from Figure 12 which the current flows toward the copper inside of the cell. If we have a circuit of low resistance to work through and desire to increase the current, we may group our cells as r-jf i - nas - ^n shown in Figure 13, where two fm I sets are in parallel. This arrange- ~zr ~ ment will give a stronger current, - - but it is necessary to see that both groups of cells have the same P^t- "H K _ 3^1 electro-motive force; if they have Figure 13 not t j ie higher one will send the current through the lower. If the two batteries are not con- nected with similar poles together, they would be on short cir- cuit, and no current could be obtained in the external circuit. CHAPTER III. Wiring Systems. There are numerous systems of electric light distribution. The oldest and the first to come into general use is shown diagramatically in Figure 14. This is the series arc system. In this system the same current passes through all of the lamps; and as more or less lamps are required the E. M. F. of the dynamo must be correspondingly increased or dimin- Figure 14 ished. This is accomplished by means of an automatic regulator connected to the dynamo. The current used with this system seldom exceeds ten amperes and large wires are never required. This system is best suited for street lighting where long distances are to be covered. In these diagrams, D represents the dynamo, and F, the "field" coils of the dynamo. With constant current systems the "fields" are usually in series with the armature of the dynamo, as shown in Fig. 14, and the lamps, so that the same current must pass through all. With constant WIRING SYSTEMS. 33 potential systems, the field coils are generally independent of the rest of the circuit. With such systems the current used in the circuit is so variable that it cannot be used in the fields. Another system, known as the multiple arc or parallel system, is shown in Figure 15. In this system the E. M. F. never varies, but the current is always proportional to the Figure 15 number of lights used. If, for instance, only one light is used, there is a current of about one-half ampere, but if ten 16 cp. lights are used there must be a current of about five amperes. Where many lights are used with this system, the main wires require to be quite large, and must always be proportional to the number of lights. This system is oper- ated usually at 110 volts and is suitable for residences, stores, factories and all indoor illumination. It is not well adapted to the transmission of light and power over long distances. The 3-wire system shown in Figure 16 combines many of Figure 16 the advantages of both the foregoing systems. As will be seen from the diagram, it consists of two dynamos connected in series and a system of wiring of one positive +, one nega- tive and a neutral = wire. So long as an equal number of 34 -MODERN ELECTRICAL CONSTRUCTION. lights are burning on both sides of the neutral wire, this wire carries no current, but should more lights be in use on one side of the system than on the other, the neutral wire will be called upon to carry the difference. If all the lights on one side are out, the dynamo on that side will be running idle. The currents in the neutral wire may be either positive or negative in direction. The principal advantage of this sys- tem is that with it double the voltage of the 2-wire systems is employed and yet the voltage at any lamp is no greater than with the use of two wires. It is customary to use 110 volts on each side of the neutral wire and this gives a total volt- age over the two outside wires of 220 volts. As the same current passes ordinarily through two lamps in series, we need, for a given number of lamps only half as much current as with 2-wire systems and can, therefore, use smaller wires. For the same number of lights and the same per- Figure 17 centage of loss the amount of copper required in the two outside wires is only one-fourth that of 2-wire systems; to this must be added a third wire of equal size for the neutral, so that the total amount of copper required with this system is y% of that of 2-wire system using the same kind of lamps. Incandescent lamps are often run in multiple-series, as in WIRING SYSTEMS. Figure 17, without a neutral wire. The number of lamps to be used in series depends upon the voltage of the dynamo. If that is 550, five 110 volt lamps are required in each group, or ten 55 volt lamps. If the filament of one lamp breaks all of the lamps in Figure 18 that group are extinguished and if one is to be used all must be used. Figure 18 shows the diagram of a series-multiple system. This style of wiring should be avoided. A diagram of an alternating current system is shown in Figure 19 Figure 19. In this system extremely high voltage is used and consequently the currents are never very great. This makes 36 MODERN ELECTRICAL CONSTRUCTION. it extremely useful for long distance transmission. Since, however, the high pressure employed cannot be used directly in our lamps it must be transformed into lower pressure. This is done by means of transformers, and it is possible to reduce the line voltage to any desirable extent. As the volt- age is reduced, however, the current increases and the wires taken from the transformers into the buildings must be as large as those for 2-wire systems using the same kind of lamps. The high pressure, or primary wires, are rarely allowed inside of buildings. The Transmission of Electrical Energy. We have seen that currents of electricity flow only in electrical conductors, and that these conductors are usually arranged in the form of wires. We have further seen that the power transmitted is proportional to the product of the volts and amperes used. The actual amount of energy trans- mitted being the product of the above multiplied by the time. Currents of electricity always encounter some resistance and in consequence of this resistance, generate heat; the generation of heat in any electric circuit being proportional to the square of the current multiplied by the resistance. This formula, I 2 X R expresses the loss of electrical energy due to the resistance of the conductors and which reappears in the form of heat. If this loss is not kept within reasonable limits, the wires will become very hot and destroy the in- sulation or ignite surrounding inflammable material. The above loss and hazard is generally guarded against by insur- ance companies and inspection boards by designation of the current in amperes which certain wires may be allowed to carry. Table No. 1 gives the currents which the National Board of Fire Underwriters has decided to consider safe and which ELECTRICAL TRANSMISSION 37 should be closely followed, and on no account should wires smaller than those indicated be used. There is no harm and no objection to using wires larger than indicated, but neither is there much gained unless the run be a long one as we shall see further on. The table of carrying capacities shows a great discrepancy between the relative cross-section of large and small wires and the currents they are allowed to carry; thus a No. 0000 wire has a cross-section about eight times as great as that of No. 6, yet is allowed to carry less than five times as much. This discrepancy arises from the different rate of heat radiation. The radiating surface or circumference of a small circle or wire is relatively to its cross-section much greater than that of a large circle, and other things being equal the ratio existing between the heat given to a body and its radiat- ing surface determine its temperature. We have seen before that the power (either for lights or motors) consists of two factors; current and pressure, ex- pressed respectively as amperes and volts. We have also seen that the power (watts) equals the product of these two; hence it follows, that as we increase either one, we may de- crease the other, or conversely, as one is decreased the other must be increased in order to deliver a given amount of power. We further know that it is the current alone which heats the wires and that accordingly as our currents are large or small, the wires used to transmit them must be large or small. It is obvious, therefore, that we can save much on copper by using higher voltages, since, if we double the voltage, we shall need only one-half as much current and can, therefore, use a much smaller wire. As an example: Sup- pose we have power to transmit which at 110 volts requires 90 amperes. This requires a No. 2 wire containing 66,370 circular mils. Now, if we double the voltage, we shall need only 45 amperes; this much we are allowed to transmit over 38 MODERN ELECTRICAL CONSTRUCTION. a No. 6 wire which has only 26,250 circular mils. We must not, however, increase our voltage without due precaution and consideration, for high voltage is dangerous to life and in- creases the fire hazard. It also increases the liability to leakage and requires better and more expensive insulation which in a small measure offsets the other advantages. The usual voltage employed at present varies from 110 to 220 volts for indoor lighting and power; 500 to 650 volts for street railway work and from 2 to 20,000 volts for long distance transmission. The higher voltages mentioned are seldom brought into buildings, and are nearly always used with some transforming device which reduces the pressure to 110 or 220 volts for indoor lighting or power. The flow of current through a given lamp, motor, or re- sistance determines the light, power or heat obtainable from such device. We know that the flow of current in turn (other things being equal) varies as the E. M. F. maintained at the terminals of any of these devices. Consequently in order to obtain a steady flow of current it is necessary to provide a steady E. M. F. The loss of E. M. F. in any wire is equal to the current flowing in that wire multiplied by the resistance of the wire. Since it is impossible to obtain wires without resistance, it is also impossible to establish a circuit without loss and wherever electricity is used some loss must be reckoned with. We may make this loss as large or as small as we 'desire. Where the cost of fuel is high, it is important to keep this loss quite small, using for that purpose larger wires. On the other hand where there is an abundance of cheap fuel, or, where, for instance, water power is used, it will be more economical to waste five or ten per cent of the electrical energy than to spend the money needed to provide the copper necessary to reduce the waste to one or two per cent. In this connection, however, it must not be overlooked that ELECTRICAL TRANSMISSION 39 the quality of the service depends to a great extent upon the loss allowed and here the nature of the business supplied must be taken into consideration. In yards, warehouses, barns, etc., a variation of five or ten per cent in candle power may not matter much, but in residences or offices it is very annoying. The loss in voltage depends, as we have already seen, upon the current used, and the resistance of the wire em- ployed. If the current is decided upon, we can reduce the loss only by reducing the resistance; the resistance can be re- duced only by increasing the size of wire used. If we double the cross-section of the wire, we decrease the resistance one- half and consequently reduce the loss or variation in volt- age one-half. Thus it will be seen that as we attempt to reduce the loss in voltage to a minimum we shall require very large wires and thus greatly increase the cost of our installation. For instance, if a line be in operation with a loss -f twenty per cent, by doubling the amount of copper, we reduce the loss to ten per cent. In order to reduce our loss to five per cent, we must again double the amount of copper; and to reduce the loss still more, say to 2 l / 2 per cent, a wire of double the cross-section of the last must be used. If the cost of copper in the original installation utilizing eighty per cent of the energy be taken as 1, then the cost of copper to utilize ninety per cent will be 2; of ninety-five per cent, 4; and of ninety-seven and one-half per cent, 8; and no amount of copper will eVer be able to save the full 100 per cent. We must not overlook, however, that although a reduction of loss from four to two per cent requires us to double the amount of copper, it does not necessarily double the cost of our installation, for in many cases it adds but a small per- centage to the total cost. For instance, if it were decided to use No. 12 instead of No. 14 wire in moulding or insulator 40 MODERN ELECTRICAL CONSTRUCTION. work,- the cost of labor would not be appreciably affected thereby; similarity in connection with a pole line, the dif- ference in total cost occasioned by the use of say No. 6 instead of No. 10 wire would be small. Calculation of Wires. In electrical calculations so far as they relate to wiring, the circular mil plays an important part, and it becomes necessary to thoroughly understand its meaning. The mil is the 1/1000 part of an inch, consequently one square inch contains 1,000x1,000 equals 1,000,000 square mils. If all elec- trical conductors were made in rectangular form, we should be able to get along nicely by the use of the square mil, but, since they are nearly all in circular form, the use of the square mil as a unit would necessitate otherwise unnecessary figures. The circular mil means the cross-section of a circle one mil in diameter, whereas the square mil means a square each side of which is equal to one mil in length. Square mils, can, therefore, be transformed into circular mils by dividing by .7854, and circular mils into square mils by multiplying by .7854, since it is well known that a circle which can be inscribed within a square bears to that square the ratio of .7854 to 1. To illustrate: Using square mils if we wish to determine the cross-section of a wire having a diameter of 50 mils, we must first square the diameter and then multiply by .7854; 50 X 50 X .7854, or 1963.5, which is the cross section of the wire expressed in square mils. To express the cross-section in circular mils, we have but to square the diameter, or 50 X 50 = 2500 circular mils. The 2500 circular mils are exactly equal to the 1963.5 square mils. The adoption of the circular mil simply eliminates the figure .7854 from the calculations. The resistance of a copper wire having a cross-section of CALCULATION OF WIRES *1 one mil and a length of one foot is from 10.7 to 10.8 ohms, the variation being due to the temperature of the wire. 10.8 ohms is the resistance usually taken. This resistance in- creases directly as the length and decreases as the cross-sec- tion increases. The resistance of any copper wire can, there- fore, be found by multiplying its length by 10.8 and dividing by the number of circular mils it contains. Expressed in L X 10.8 formula this becomes R= where L stands for the C. M. total length of wire in feet, and C. M. for the cross-section in circular mils, and R for the resistance in ohms. In order to find the loss in volts, we must multiply the resistance by the current used. Representing this current by I, the I X L X 10.8 formula becomes = V; V being the volts lost. C. M. It is, however, seldom necessary to find how many volts would be lost with a certain wire and current, but rather to find how many circular mils are necessary in a wire so that the volts lost may not exceed a certain percentage. In order to determine this, we transpose V and C. M. and the formula now becomes I X L X 10.8 = C. M. This is the final formula and gives V directly the number of circular mils a wire must have so that the loss with this current and length of wire shall not exceed the limits set by V. As an example, we have a current of 20 amperes to trans- mit a distance of 200 feet and the bss shall not exceed two per cent; voltage 110. This requires 400 feet of wire (two wires 200 feet long) and two per cent of 110 is 2.2. We therefore have 20 X 400 X 10.8 divided by 2.2, which gives us 39,270 circular mils, which we see by table I is a little less than a No. 4 wire. 42 MODERN ELECTRICAL CONSTRUCTION. The above formula will answer for all 2-wire \vork> whether it be lights or power. It is simply necessary to find the current required with whatever devices are to be used. These calculations are not often made in actual practice. It is much easier to refer to tables such as II, III, IV, V, VI, given at the end of this volume, by which the proper size of wire can be determined at a glance almost. In connection with 3-wire systems using two lamps in series, we need to calculate the two outside wires only, the neutral wire should then be taken of the same size. We must however assume double the voltage existing on either side of the neutral; that is to say, a 2-wire system using 110 volts would be figured at 110 volts, while a 3-wire system, using 110 volt lamps on each side of the neutral wire would be figured at 220 volts. It must also be noted that with 3-wire systems the cur- rent required is only l /z of that required with 2-wire sys- tems. Ordinarily we have two lamps in series and the same current passes through both. Applying this to our formula we see that with the 3-wire system the current I is only half as great as with 2-wire systems and (the percentage of loss in both cases being the same) V, which stands for the volts to be lost, becomes twice as great. Owing to these two fac- tors, the wire for 3-wire systems need have only % as many circular mils as that of a 2-wire system with the same per- centage of loss. To this must be added the neutral wire so that the total cost of wire must be Yt, of that for the 2-wire systems. The amount of copper required in power transmission for a given percentage of loss varies as the square of the voltage employed. By doubling the voltage we can transmit power with the same loss four times as far; or, if we do not change distance or wire, we shall have only one-fourth of the loss CALCULATION OF WIRES 43 we had before. A practical idea of the laws governing the distribution of circuits and the losses in voltage and wire which are unavoidable may be gained from Figure 20. Figure 20 shows 96 incandescent lights arranged on one floor and placed 10 feet apart each way. With all cutouts placed at A and circuits arranged as in No. 1, 2,080 feet of branch wiring for the eight circuits of 12 lights each, will be required. If the cutouts be placed in the center, B, the same length of wire will be necessary. We have in this case merely transferred the cross wires from one end of the hall to the center. If we arrange two sets of cutouts as at C and D and run circuits as 3 and 4 the total amount of wire necessary will be only 1,920 feet. By this arrangement we avoid the necessity of crossing the space indicated by dotted lines at the right, opposite B. If we run the circuits on the plan of No. 2, the least amount of wire for the eight circuits will be 2,560 ft. Such wir- ing would require extra wires feeding the various groups. Should we run a set of mains along ACBD, and make 12 circuits of the installation by placing one cutout for each eight lights, the amount of wire required will be 1,680 feet. If we run a set of mains through B as shown by dotted lines using 12 lights per circuit, 1,760 feet of wire will be re- quired. If we now double the number of lights in the same space or limit the number per circuit to six, we shall require 3,200 feet of wire to feed them all from A, but only 2,400 to feed them from B ; to feed them all from the two centers C and D will also require 2,400 feet. The most economical location of cutout centers will, with even distribution of light, and in regard to branch wiring only, be such that it is unnecessary to run circuits like No. 2; in other words, not more than the number of lights allowed on one circuit should lead away from it in one direction. Suppose, for instance, the number of lights be increased 44 MODERN ELECTRICAL CONSTRUCTION. &> US ^TA) /o u 10 u 1 /OB ) ( ( ~^^j C | 3 I * ; ( 1 , c | to ) ( -r r | | c~l f / ( XI 4 s ) (, a >o?.e I 1 1 ( ( 3 1 z C 1 q i C 1 3 P 1 r i l k t- (DJI * s ^ i ( 1 < ) I g - c G L : C C ( 3 2 J i " - : c ( D Figure 20 CALCULATION OF WIRES 45 by one-half or (which amounts to the same thing in wire), the number of lights per circuit be limited to eight. If we run all branch circuits from A, we shall need a total of 2,760 feet. It will require just as much wire to run the 64 lights below X as was required to run the whole 96 before ; viz. : 2,080 feet ; to this must be added the wire necessary to run the four circuits above which is 680 feet. By extending our mains to the point X, we car save eight runs of wire each equal in length to the distance between A and X. X is the point of extreme economy as regards branch wires and nothing can be gained in this respect by extending the mains any further unless several cutout centers are decided upon as before explained. Whether it be more economical to extend the mains to X, or run branch circuits from A, depends upon the relative cost, in this instance, of 30 feet of mains and 480 feet of branch wires. With an uneven distribution of lights as indicated by the black circles, each of which may be taken as an arc lamp or cluster of incandescent lamps, the most economical location of cutouts will be at Z. To move them farther to the right would shorten the wires of five circuits and lengthen them on eight ; to move either up or down in the group of eight would also lenghten more wires than it would shorten. In laying out circuits for electric lights, however, we must not take into consideration the cost of wire only. In many cases the loss in voltage is of far greater importance, not only because it means a steady waste of power, but also because of unsatisfactory illumination, lamps in different parts of a circuit not being of the same candle power, or the light in one place varying greatly when lights in another place are turned on or off. Some idea of the variation in voltage in different parts of differently arranged circuits can be obtained from Figure 20. The length of wire in circuit 1 is 35 feet to the first lamp and 46 MODERN ELECTRICAL CONSTRUCTION. 10 feet from this to the next, etc. The voltage at the cut- out A is 110 and at each lamp is given the actual voltage existing at that point with all lamps burning. The wire of the circuit is No. 14 and with 55 watt lamps, the loss to the last lamp over a run of 145 feet is a trifle over two and one- half per cent when all lamps are burning. Circuit No. 2 is figured as of the same length as No. 1, and supplies the same number of lamps, but ct a much greater loss, slightly over four per cent to the last lamp. Circuits 3 and 4 feeding from C contain equal lengths of wire, but there is quite a difference in loss; in 3 only .75 of one volt, while in 4 it is a little over two volts. From study of Figure 20 we may learn that the arrangement of circuit 1 is fairly satisfactory especially if the nature of the work done under it is such that only part of the lamps are used at the same time. Circuit No. 2 is bad if all lights are used at once, and it should be wired with No. 10 or 12 wire. Whenever the loca- tion of lights is such as to allow a circuit like No. 3 to be run, the loss can be kept very low with a minimum of wire. In general the more cutout centers there are established in propor- tion to the number of lights, if mains are properly arranged, the less will be the loss in pressure and the more satisfactory the service. NOTICE. DO NOT FAIL TO SEE WHETHER ANY RULE OR ORDINANCE OF YOUR CITY CONFLICTS WITH THESE RULES. CLASS A. STATIONS AND DYNAMO ROOMS. Includes Central Stations, Dynamo, Motor and Storage- Battery Rooms, Transformer Substations, Etc. 1. Generators. a. Must be located in a dry place. Perfect insulation in electrical apparatus requires that the material used for insulation be kept dry. While in the con- struction of generators the greatest care is taken, so that all current carrying parts are well insulated, still, if moisture is allowed to settle on the insulation, trouble is almost sure to occur. For this reason a generator should never be installed where it will be exposed to steam or damp air, or in any place, where through accident, water may be thrown against it. b. Must never be placed in a room where any hazardous process is carried on, nor in places where they would be ex- posed to inflammable gases or flyings of combustible materials. In even the best constructed dynamos there is always more or less sparking at the brushes and small pieces of hot carbon are sometimes thrown off. As a general rule in buildings where there is considerable dust, such as in wood-working plants, grain elevators and the like, the dynamo is located in the engine room, which is generally isolated from the dusty part of the building. c. Must be thoroughly insulated from the ground wherever feasible. Wooden base-frames used for this purpose, and 48 MODERN ELECTRICAL CONSTRUCTION. wooden floors which are depended upon for insulation where, for any reason, it is necessary to omit the base-frames, must be kept filled to prevent absorption of moisture, and must be kept clean and dry. Where frame insulation is impracticable, the Inspection Department having jurisdiction may, in writing, permit its omission, in which case the frame must be permanently and effectively grounded. A high-potential machine, which on account of great weight or for other reasons, cannot have its frame insulated from the ground, should be surrounded with an insulated platform. This may be made of wood, mounted on insulating supports, and so arranged that a man must always stand upon it in order to touch any part of the machine. In case of a machine having an insulated frame, if there is trouble from static electricity due to belt friction, it should be overcome by placing near the belt a metallic comb connected with the earth, or by grounding the frame through a very high resistance cf not less than 300,000 ohms. The smaller generators are usually insulated on wooden base frames. A base frame suitable for this work is shown in Figure 21 Figure 22 Figure 21. Almost any kind of wood, well varnished, is very good for this purpose. The base frame is screwed to the floor or foundation and the slide rail (which is used where the dy- namo is belted to the engine to allow the tightening and slack- GENERATORS 49 ening of the belt) is independently attached to it, that is, the same bolt must not be used to hold the slide rail to the base frame and the base frame to the floor, as this would be liable to ground the frame. The direct connected machines (dynamo and engine on same bed plate) are often insulated by the use of mica washers and bushings surrounding the bolts which fasten the dynamo to the bed plate and by using an insulated flange coupling between the shaft of the dynamo and that of the engine. Figure 22 shows a section of a flange coupling insulated in this way, the heavily shaded parts rep- resenting the insulating material. The larger machines, which on account of their weight cannot be insulated, must be permanently and effectually grounded. Where the engine and dynamo are direct con- nected a very good ground is obtained through the engine con- nections. Where belts arc used a good ground can be ob- tained by fastening a copper wire under one of the bolts on the dynamo and connecting the other end of the wire to available Figure 23 water pipes. In the case of high tension machines, especially series arc, the machine should always be surrounded by an insulated platform so arranged that a man must stand on it in order to touch any part of the machine either live parts or SO MODERN ELECTRICAL CONSTRUCTION. frame and in handling such a machine only one hand at a time should be used. A hardwood platform mounted on insulators will serve very well for this purpose or suitable platforms may be obtained from dealers in electrical supplies. Figure 23 shows a metallic comb such as is occasionally used to overcome the static electricity due to the friction of the belt. A strip of metal, one end of which is cut with a number of projecting points, is suspended crosswise a short distance above the belt. A wire connects this plate to any suitable ground. A resistance for grounding the generator frame in accord- ance with this rule is constructed of ground glass equipped with two metal terminals separated a short distance and con- nected by means of a lead pencil mark. One terminal is con- nected to the frame of the machine and the other to the ground. d. Every constant-potential generator must be protected from excessive current by a safety fuse, or equivalent device of approved design in each lead wire. These devices should be placed on the machine or as near it as possible. Where the needs of the service make these devices imprac- ticable, the Inspection Department having jurisdiction may, in writing, modify the requirements. The fuses required by this rule are often mounted on the dynamo, but the general practice at the present time is to mount all fuses on the switchboard. A fuse should be placed in each lead ; that is, each of the main wires from the dynamo should be protected by a fuse. A fuse should never be placed in the field circuit wire. Where two or more dynamos are run in parallel the equalizer connection (a wire connecting all the armature terminals from which the series fields are taken and which tends to equalize the load between the various ma- chines) is sometimes carried through a 3-pole switch on the switchboard and is often fused. It is immaterial whether this equalizer is fused or not, as fusing it adds no protection. If it GENERATORS 51 is fused the fuse should be at least the same size as used in the leads. Circuit breakers are very often used for the protection in the dynamo leads. They are generally mounted on the switch- board and connected in the circuit ahead of the main switch. As a general rule circuit breakers are not approved unless fuses are also installed in the circuit. The circuit-breaker as at present constructed is in nearly all cases a much more efficient and reliable device than the fuse, and its use is to be recommended. Single-pole circuit breakers are approved if fuses are also used. As to the relative currents at which the fuse and circuit breaker should be set to operate, authorities differ. Some advise both to be set to operate at the same current strength, so that the fuse, which takes a longer time to operate, will blow only in case the circuit breaker fails. Another recom- mends the fuses to be of such capacity as to carry any load which will be required of them and to set the circuit breaker a little higher than the fuses, so that the fuses will operate on overload and the circuit breaker on short circuit. The practice of setting the fuses at about twenty-five per cent, above the circuit breaker seems to be preferred, for it occasionally happens when both are set to operate at the same current, the fuse alone will "blow," due to the excessive heat produced in the fuse at full load. Cases are sometimes found where the cessation of current due to the blowing of a fuse could cause more damage than would result from an overload, as, for instance, where the dynamo operates some safety device. In cases of this kind the Inspection Department having jurisdiction may modify the requirements. e. Must each be provided with a waterproof cover. f. Must each be provided with a name-plate, giving the maker's name, the capacity in volts and amperes, and the nor- mal speed in revolutions per minute. 52 MODERN ELECTRICAL CONSTRUCTION. 2. Conductors. From generators to switchboards, rheostats or other instru- ments, and thence to outside lines. a. Must be in plain sight or readily accessible. b. Must have an approved insulating covering as called for by rules in Class "C" for similar work, except that in central stations, on exposed circuits, the wire which is used must have a heavy braided, non-combustible outer covering. Bus bars may be made of bare metal. Rubber and "weatherproof" insulations ignite easily and burn freely. Where a number of wires are brought close to- gether, as is generally the case in dynamo rooms, especially about the switchboard, it is therefore necessary to surround this inflammable material with a tight, non-combustible outer cover. If this is not done, a fire once started at this point would spread rapidly along the wires, producing intense heat and a dense smoke. Where the wires have such a covering and are well insulated and supported, using only non-com- bustible materials, it is believed that no appreciable fire hazard exists, even with a large group of wires. c. Must be kept so rigidly in place that they cannot come in contact. d. Must in all other respects be installed with the same precautions as required by rules in Class "C" for wires carry- ing a current of the same volume and potential. In wiring switchboards, the ground detector, volt meter and pilot lights must be connected to a circuit of not less than No. 14 B. & S. gage wire that is protected by a standard fuse block; this circuit is not to carry over 660 watts. A number of different methods are used for running wires in dynamo rooms. Where the dyanmo is located in a room with a low ceiling, or where it is not desirable to run the wires open, metal conduits may be imbedded in the floor and the wires run in them. If the engine room is located in the basement or in any place where water or moisture is liable to gather in the conduits the wires should be lead covered. At outlets the conduits should be carried some distance above the floor level and close to the frame of the machine, where they will be protected from mechanical injury. If the space under the machine will allow it, the conduit should be ended SWITCHBOARDS S3 there where it will be protected by the base frame. Where lead covered wires are used, the lead should be cut back some distance from the exposed part of the wire and the end of the lead should be well taped and compounded so that no moisture can creep in between the lead and the insulation. In place of the metal conduits tile ducts can be used ; or, if the floor is of cement, a channel may be left in the floor and the wires run in it. A removable iron cover should be provided. The wires may be run open on knobs or cleats as described in Class C. Where there are many wires, cable racks, con- structed of wood or preferably iron, having cleats bolted to them, may be used. As a general rule moulding should not be used for this class of work. Especially in central stations the generators are often called upon for a very heavy overload and should the wires become overheated a fire is much more apt to result than if the mains were run open where any trouble could be immediately noticed. 3. Switchboards. a. Must be so placed as to reduce to a minimum the danger of communicating fire to adjacent combustible material. Special attention is called to the fact that switchboards should not be built down to the floor, nor up to the ceiling. A space of at least 10 or 12 inches should be left between the floor and the board, and 3 feet, If possible, between the ceiling and the board, in order to prevent fire from communicating from the switchboard to the floor or ceiling, and also to pre- vent the forming of a partially concealed space very liable to be used for storage of rubbish and oily waste. b. Must be made of non-combustible material or of hard- wood in skeleton form, filled to prevent absorption of moisture. If wood Is used all wires and all current-carrying 1 parts of the apparatus on the switchboard must be separated therefrom by non-combustible, non-absorptive insulating material. c. Must be accessible from all sides when the connections are on the back, but may be placed against a brick or stone wall when the wiring is entirely on the face. 54 MODERN ELECTRICAL CONSTRUCTION. If the wiring Is on the back, there should be a clear space of at least 18 inches between the wall and the apparatus on the board, and even if the wiring is entirely on the face, it is much better to have the board set out from the wall. The space back of the board should not be closed in, except by grating or netting either at the sides, top or bottom, as such an enclosure is almost sure to be used as a closet for clothing or for the storage of oil cans, rubbish, etc. An open space is much more likely to be kept clean, and is more convenient for making repairs, examinations, etc. d. Must be kept free from moisture. e. On switchboards the distances between bare live parts nl Figure 24 of opposite polarity must be made as great as practicable, and must not be less than those given for tablet-boards (see No. oo A). The switchboard may be located in any suitable place in the RESISTANCE BOXES 55 dynamo room. It should generally be placed in a central position as close as possible, without inconvenience, to all machines and perfectly accessible. Do not locate a switchboard under or near a steam or water pipe or too close to windows, as these may accidentally be the means of wetting the board. The material generally used for the construction of switch- boards is slate or marble, free from metallic veins. If metallic veins are not guarded against they may cause great leakage of current, which will manifest itself in heating the slate or marble. The switchboard may be made of hardwood in skeleton form (see Figure 24), but in this case all switches, cutouts, instruments, etc., must be mounted on non-combustible, non- absorptive insulating bases, such as slate or marble and all wires must be properly bushed where they pass through the woodwork and must be supported on cleats or knobs. Wood base instruments are not approved. Marble or slate boards are usually set in angle iron frames and are much safer and better than the skeleton board shown. It is a good plan to have the iron legs rest on a wooden base, so that they will be insulated from the ground. Although only 18 inches clear space is required back of the board, where the board is back connected, this should be increased wherever possible, especially in the case of large boards. 4. Resistance Boxes and Equalizers. (For construction rules, see No. 60.) a. Must be placed on a switchboard or, if not thereon, at a distance of at least a foot from combustible material, or separated therefrom by a non-inflammable, non-absorptive, insulating material such as slate or marble. The attachments of the separating material to its support and to the device must be independent of each other, and the separating material must be continuous between the device and the support; that is, the use of porcelan knobs will not be accepted. 56 MODERN ELECTRICAL CONSTRUCTION. Ordinarily the dynamo field rheostat is mounted on the back of the board if the board is back connected, a small hand wheel being provided so that ___ the rheostat may be operated [ from the front of the board. If the switchboard is in skele- ton form, or if the rheostat is placed on a wall, it should be mounted on a solid piece of slate or marble. Separate screws should be used for at- r i g 5. taching the rheostat to the slate or marble and the slate or marble to the wall, for, if the same screws were used for this purpose, they would be apt to ground the rheostat frame. (See Figure 25.) On central stations where current is furnished over a large area, there is on some of the circuits, especially the long ones, a considerable "drop," or loss of potential. In order to keep the voltage at the point of supply on these circuits at the proper value, the voltage at the station must be raised. This in turn causes the voltage on those circuits near the dynamo to become excessive. Equalizers, which are large resistance boxes generally constructed of iron wire or strips, and capable of carrying a heavy current, are connected in the circuits and adjusted at such resistances as to make the voltage at the various points of supply uniform. They are generally too heavy to mount on the board, but should be raised on non- combustible, non-absorptive, insulating supports and should be separated from all inflammable material. b. Where protective resistances are necessary in connec- tion with automatic rheostats, incandescent lamps may be used, provided that they do not carry or control the main current or constitute the regulating resistance of the device. When so used, lamps must be mounted in porcelain recep- LIGHTNING ARRESTORS 57 tacles upon non-combustible supports, and must be so arranged that the}' cannot have impressed upon them a voltage greater than that for which they are rated. They must in all cases be provided with a name-plate, which shall be permanently at- tached beside the porcelain receptacle or receptacles and stamped with the candle-power and voltage of the lamp or lamps to be used in each receptacle. 5. Lightning Arresters. ( For construction rules, sec No. 63.) a. Must be attached to each wire of every overhead cir- cuit connected with the station. It is recommended to all electric light and power companies that arresters be connected at intervals over systems in such numbers and so located as to prevent ordinary discharges en- tering (over the wires) buildings connected to the lines. b. Must be located in readily accessible places away from combustible materials, and as near as practicable to the point where the wires enter the building. Station arresters should generally be placed in plain sight on the switchboard. In all cases, kinks, coils and sharp bends in the wires be- tween the arresters and the outdoor lines must be avoided as far as possible. c. Must be connected with a thoroughly good and perma- nent ground connection by metallic strips or wires having a conductivity not less than that of a No. 6 B. & S. gage copper wire, which must be run as nearly in a straight line as possible from the arresters to the ground connection. Ground wires for lightning arresters must not be attached to gas pipes within the buildings. It Is often desirable to introduce a choke coil in circuit between the arresters and the dynamo. In no case should t^.e ground wires from the lightning arresters be put into ircn pipes, as these would tend to impede the discharge. A lightning discharge is simply a discharge of electricity at 58 MODERN ELECTRICAL CONSTRUCTION. very high potential. While the insulation of the ordinary wire serves very well for the voltages for which it is used it offers very little resistance to a current of such high potential, and providing the discharge can reach the ground by jumping through the insula- tion, it will generally take that course unless some easier path is offered to it. A lightning arrester in its simplest form consists of Fig. 26. two metal plates separated by a small air space as shown in Fig- ure 26. One of the plates is con- nected to the line and the other to the ground, a set being pro- vided for each line wire to be protected. The air space between the metal plates offers a much lower resistance to the passage of such a sudden current as a dis- charge of lightning consists of, than do the magnets of a dynamo, for instance, or highly insulated parts of the line. The current, therefore, jumps the air space and passes to ground. When the current jumps this air space it produces an arc similar to that seen in an arc lamp, and after the light- ning discharge is over the dynamo current is very likely to maintain this arc and thus cause a short circuit from one lightning arrester through the ground to the other. Different methods of preventing this by interrupting the arc have been devised. Figure 27 shows the T. H. lightning arrester, in which the arc is extinguished by a magnetic field set up by the electro- magnet. In the Wurts non-arcing lightning arrester (Figure 28) the discharge takes place across the air gaps between the cylinders ; these are made of a metal which will not arc. A choke coil is essentially an electro-magnet, and like all TESTING 59 magnets offers a ve.ry high resistance to a sudden rise in cur- rent strength, and is, therefore, an additional protection to other magnets in the circuit. 6. Care and Attendance. a. A competent man must be kept on duty where gen- erators are operating. Figure 27 b. Oily waste must be kept in approved metal cans and removed daily. Approved waste cans shall be made of metal, with legs raising can 3 inches from the floor and with self-closing covers. 7. Testing of Insulation Resistance. a. All circuits except such as are permanently grounded in accordance with Rule 13 A must be provided with reliable ground detectors. Detectors which indicate continuously and 60 MODERN ELECTRICAL CONSTRUCTION. give an instant and permanent indication of a ground are preferable. Ground wires from detectors must not be at- tached to gas pipes within the building. b. Where continuously indicating detectors are not feasible the circuits should be tested at least once per day, and prefer- ably oftener. c. Data obtanied from all tests must be preserved for ex- Figure 28 animation by the Inspection Department having jurisdiction. These rules on testing to be applied to such places as may be designated by the Inspection Department having jurisdic- tion. The exceptions to this rule are 3-wire direct current sys- tems where the neutral is grounded and 2 and 3-wire alter- nating current secondaries where the neutral or one side is grounded. TESTING 61 In every installation of electric wiring there is a certain "leak" of current. This leak is partly between the wires and the ground and between the wires themselves. The amount of leak varies, but is always dependent on the insulation resist- ance. Where a small amount of wire is well installed the leak" should be very small, but in the case of large installations or where the wiring has been poorly done the flow of current to ground or between the wires of opposite polarity may be- come quite large. Wires lying on pipes or on damp wood- work, crossed wires or live parts of apparatus mounted on wooden blocks, all tend to cut down the insulation resistance and increase the leak. The effects of poor insulation are : First, it represents a useless loss of current, and, second, and more important, it means a possible cause of fire. The simplest way to determine the insulation resistance of a circuit is by means of a voltmeter. In Figure 29 if a volt- meter of known resistance is connected between one side of the circuit and the ground and there is a ground on the other side of the circuit, say at X, current will flow from the positive wire through the voltmeter then through the ground at X to the negative side of the circuit. The voltmeter needle will indicate a certain reading which we will call V 1 . If the volt- meter is now connected directly across the circuit we get the circuit voltage, which we will call V. The two readings, V 1 and V, are to each other as the resistance of the voltmeter is to the combined resistance of the voltmeter and the gnound at X; or, calling the resistance of the voltmeter R and the resist- yi R V - V 1 ance of the ground at X r, we get = , or r R . V R + r V 1 As an example : On a certain system the voltage across the mains is 110, while with the voltmeter connected as shown in Figure 29 we obtain a reading of 30. The resistance of the voltmeter is 10,500 ohms. Supplying the numbers in the for- 62 mula groui MODERN ELE< 110-30 r 10 500 """ ~~ :TRICAL CONSTRUCTION. = 28,000 ohms as the resistance t of the system. If the voltmeter 30 id of the negative side (J) HI" III* + -^ + _a f r -^ i - Figure 29 Figure 30 connected to ground from the other side, or main, the resist- ance to ground of the + side can be obtained. If both sides of the system are grounded as at x and y, Figure 30 the voltmeter will be robbed of part of the current which would pass through it if Y were not in parallel with it. It will therefore not indicate correctly under such circum- stances. If, however, tests are frequently made and defects cleared up at once when noticed, it will seldom happen that two grounds occur on the system at the same time. An engineer or dynamo tender will soon learn what the in- sulation resistance of the plant in his charge should be and be governed ac- cordingly. A diagram of a direct current ground detector switch is shown in Figure 31. By throwing switch A down the bus bar is connected to the ground through the voltmeter and by throwing switch B the + bar is connected to ground through the voltmeter. The ground wire should be run to a water or steam pipe .p^rcu LUC o i Hffl MOTORS 63 (never to a gas pipe) or to some grounded part of the building. If no good ground is obtainable one may be made as described under 13 A. 8. Motors. a. Must be thoroughly insulated from the ground wherever feasible. Wooden base-frames used for this purpose, and wooden floors which are depended upon for insulation where, for any reason, it is necessary to omit the base-frames, must be kept filled to prevent absorption of moisture, and must be kept clean and dry. Where frame insulation is impracticable, the Inspection Department having jurisdiction may, in writing, permit its omission, in which case the frame must be permanently and effectively grounded. A high-potential machine which, on account of great weight or for other reasons, cannot have its frame insulated, should be surrounded with an insulated platform. This may be made of wood, mounted on insulating supports and so arranged that a man must stand upon it in order to touch any part of the machine. In case of a machine having an insulated frame, if there is trouble from static electricity due to belt friction, it should be overcome by placing near the belt a metallic comb connected to the earth, or by grounding the frame through a very high resistance of not less than 300,000 ohms. Where motors with grounded frames are operated on sys- tems where one side is either purposely or accidentally grounded there exists a certain difference of potential be- tween the windings and the motor frame ; this difference of potential depending on the part of the circuit considered. At some places in the winding it will be the full difference of po- tential at which the motor is operating and at other points practically nothing. Should the conductors accidentally come in contact or "ground" on the motor frame a short circuit would result, as the circuit would then be completed through the motor frame and ground. To obviate this the motor frame should be insulated from the ground. This may be done either by setting the motor on a wood floor or by the use of a base 64 MODERN ELECTRICAL CONSTRUCTION. frame, as with generators. A base frame should always be used where possible, for when a motor is set directly on the floor it is often impossible to keep the space under it clean, and there is always a liability of the floor being damp or of nails in the floor passing through the woodwork into some grounded part of the building or metal piping. A properly constructed base frame will allow of easy cleaning of the space under the motor. In the case of elevator or other motors where the shunt field is suddenly broken, a momentarily high voltage is induced in the field windings. If the frame of the motor is grounded this high voltage has a strong tendency to jump through the insulation of the wires to the metal work of the motor thus grounding the circuit. b. Must be wired with the same precautions as required by rules in Class "C" for wires carrying a current of the same volume and potential. Circuits for motors may be -run in any of the ways described in Class "C" ; either open on knobs or cleats, in moulding, concealed knob and tube work or in conduit ; or any combina- tion of these may be used. The conditions in each case will de- termine which is the best method to use. Where motors are placed some little distance from their switches and starting boxes, as in printing press work, conduit is often used for the wiring between the switch and starting box and the motor. This method provides very good mechanical protection for the wires and affords a safe way of running them. The motor leads or branch circuits must be designed to carry a current at least twenty-five per cent, greater than that for which the motor is rated, in order to provide for the in- evitable occasional overloading of the motor, and the increased current required in starting, without over-fusing the wires. The use of voltages above 550 is rarely advisable or neces- sary, and will only be approved when every possible safeguard has been provided. Plans for such installations should be sub- mitted to the Inspection Department having jurisdiction before any work on them is begun. MOTORS 65 Good values to use for calculating the size of wire for branch conductors are given below. The question of loss of voltage is not taken into consideration here. 110 volts 9.3 amperes per horsepower 220 volts 4.6 amperes per horsepower 500 volts 2 amperes per horsepower For mains supplying many motors it is not necessary to provide the twenty-five per cent, overload capacity, because it is not likely that all motors will start at the same time. If, however, any one motor has more than half the capacity of the whole installation, it is advisable to provide the overload capacity. For instance, if two motors, each of 50 amperes capacity, are fed over a line of 100 amperes capacity and one is started while the other is working at full load, they will overload that line twelve and one-half per cent. For mains supplying many small motors the size should be chosen for the total load connected, using the following values : 110 volts 7.5 amperes per horsepower 220 volts 3.75 amperes per horsepower 500 volts 1.65 amperes per horsepower Where there are a number of 110-volt motors installed on the Edison 3-wire system, providing the load is evenly balanced between the two sides, the mains may be figured as though the motors were operating at 220 volts. The reason for this will be easily seen when it is remembered that two 110-volt motors operating in series on 220 volts (as they do on the Edison 3-wire system) take only one-half the current they would if operated on a straight 2- wire 110-volt system. c. Each motor and resistance box must be protected by a cut-out and controlled by a switch (see No. 17 a), said switch plainly indicating whether "on" or "off." With motors of one- fourth horsepower or less, on circuits where the voltage does MODERN ELECTRICAL CONSTRUCTION. not exceed 300, No. 21 d must be complied with, and single pole switches may be used as allowed in No. 22 c. The switch and rheostat must be located within sight of the motor, except in cases where special permission to locate them elsewhere is given, in writing, by the Inspection Department having juris- diction. Where the crcuit-breaking device on the motor-starting rheostat disconnects all wires of the circuit, the switch called for in this section may be omitted. Overload-release devices on motor-starting rheostats will not be considered to take the place of the cut-out required by this section if they are inoperative during the starting of the motor. The switch is necessary for entirely disconnecting the motor when not in use, and the cut-out to protect the motor from excessive currents due to accidents or careless handling when starting. An automatic circuit-breaker, disconnecting all wires of the circuit may, however, serve as both switch and cut-out. For the larger size motors a cut-out must be installed for each motor, but with motors of J4 horsepower or less, where Figure 32 the voltage does not exceed 300, a cut-out need be installed for every 660 watts only. This allows about 5 1/8 horsepower motors, 31/6 horsepower motors or 2 % horsepower motors MOTORS 67 on one cut-out. . Every motor, whether large or small must be controlled by a switch which will indicate whether the cur- rent is on or off. This is required to reduce the liability of a motor being accidentally left in circuit, which might result in serious trouble. Figure 32 shows a complete motor installa- tion as usually arranged. As a general rule fused knife switches are used for the larger motors, while with the smaller motors cut-out blocks and indicating snap switches are often used. If the motor is J4 horsepower or less, and operated on a circuit where the voltage does not exceed 300, a single pole switch may be used. For all motors over J4 horsepower, and for all motors operated on voltages over 300, double pole switches must be used. The object of locating the switch and starting box within sight of the motor is that, should any trouble occur when the motor is being started, such as a short circuit or overload, it will be immediately noticed and the current shut off. If the con- ditions are such that it is necessary to locate the motor out of sight of the switch and starting box the motor should be located in a safe place, away from inflammable material. A special permit should be obtained from the inspection depart- ment having jurisdiction in order that the exact conditions may be noted. d. Must have their rheostats or starting boxes located so as to conform to the requirements of No. 4. The use of circuit breakers with motors is recommended, and may be required by the Inspection Department having jurisdiction. To be safe a rheostat should have as great a carrying ca- pacity as the motor itself, or else the arm should have a strong spring-throw attachment, so arranged that it cannot remain at any intermediate position unless purposely held there. Specifications governing the construction of rheostats are given in No. 60. Starting rheostats and auto-starters should be treated about the same as knife-switches, and in all wet, dusty or linty places should be enclosed in dust-tight, fireproof cabinets. If a special motor room is provided, the starting apparatus and safety de- vices should be included within it. Where there is any liability 68 MODERN ELECTRICAL CONSTRUCTION. of short circuit across their exposed live parts being caused by accidental contacts, they should either be enclosed in cabinets, or else a railing should be erected around them to keep un- authorized persons away from their immediate vicinity. In some cities the local rules allow the starting box or rheostat to be mounted on asbestos board, in which case it must be mounted out from the wall on porcelain knobs so that there will be at least one inch air space between the wall and the current-carrying parts. If the starting box or rheostat is to be mounted on a wall or other support where the frame would be grounded, it may be attached to a wood support and the wood support then independently attached to the wall. The best construction is to use slate or marble. If slate or marble is used it must be a continuous piece which will entirely cover the space back of the rheostat and the frame of the rheostat should be screwed to the slate or marble and the slate or marble then independently screwed to the wall, never using the same screw for attaching both. A starting box is a device for limiting the current strength during the starting of the motor by inserting a resistance in series with the armature. The ohmic resistance of the arma- ture of a shunt or compound wound motor is ordinarily very small. When such a motor is at rest and the current thrown directly on, the full voltage is thrown across the small resist- ance of the armature. Consider for a moment the case of a 1 horespower 110 volt motor having an armature resistance of say 2 ohms, and taking, when running normally, 8 amperes. Suppose the current were thrown on without the use of a starting box. According to Ohm's law the current through the armature would be 110/2 55 amperes. The results, were 55 amperes sent through the armature, can easily be imagined. Now, suppose a resistance of 8 ohms were inserted in series with the armature when starting. In this case 110/10=11 amperes only would have to pass through the armature and this the armature can easily stand. As the motor begins to revolve a counter electro-motive force is generated which op- poses the inrush of current. This counter electro-motive force increases until the motor reaches full speed and takes its nor- mal current. In the example given above at the first step of the starting box there will be a current of 11 amperes flowing through a resistance of 8 ohms and the power consumed will be equal to I 2 R, or 968 watts, which are lost in heat produced in the resistance wire. As this amounts to more than one horsepower thrown off in heat the advisability of mounting the rheostat away from inflammable material and of properly ventilating it can readily be seen. Figure 33 shows an illustration of an automatic starting box, and a diagram of the connections to a motor circuit. It Figure 33 will be seen that the resistance coils are in series with the armature circuit. As the arm A is moved to the right, resist- ance is gradually cut ont of the armature circuit until the arm reaches the last point, where it is automatically held in 70 MODERN ELECTRICAL CONSTRUCTION. position by means of the small magnet M, which is connected in series with the field circuit. By tracing out the circuits it will be found that the field connection is made on the first point of the rheostat, so that when the arm A is in the "off" position there is no current passing through the field coils. AAA/V 1 vwwws Figure 34 It will also be noticed that the last contact upon which the arm rests when "off" is dead. If the supply current for any reason fails, current will cease to flow around the coils of the magnet M and it will become demagnetized, thus allowing the arm A to fly back to the "off" position. This overcomes the possibility of the main current being momentarily shut off and then thrown on when all the resistance is out of the arma- ture circuit. This device is known as "no-voltage" release. Another device known as the "overload" release is shown in Figure 34, with a diagram of the connections. The wind- ing of the magnet M 1 carries the main current. When the current exceeds a certain amount (which can be regulated by a small nut) the armature below the magnet will MOTORS 71 be attracted, thus short circuiting the coil M and allowing the arm to fly back and shut off the current to the motor. This device cannot be considered to take the place of the regular cut-outs, as it is not operative during the starting of the motor. It can only operate after the arm A is held in position by the magnet M. Starting boxes are made in different designs to meet the re- quirements of the various classes of work on which they are used. Figure 35 shows a large automatic starting box where the resistance is cut out by the action of the solenoid S, which Figure 35 draws up the movable arm. When solenoids are used for this purpose it is often advisable to arrange the connections so that when the movable arm has been raised to the highest and last point a resistance will be inserted in series with the solenoid to cut down the current and reduce the heating in the coil, 72 MODERN ELECTRICAL CONSTRUCTION. as less current is required to hold the arm in place than to move it over the contacts. Incandescent lamps are often used for this purpose and must be installed as in 4, Class A. A speed controller differs from a starting box mainly in the size of wire used as resistance. The resistance coils of a Figure 36 starting box are wound with comparatively small wire con- nected in circuit for a short time only, generally from ten to twenty seconds, while in a speed controller the wire must be of sufficient size to carry the current as long as the motor is run- ning. Another difference between the starting box and speed controller is the automatic, coil, (Fig. 33) M, which in the speed controller is arranged to hold the arm A in any position in which it may be placed. This is accomplished in some types of speed controllers by a lever attached to an armature, which. 73 is attracted by the magnet M, the other end of the lever fitting into a series of indentations on lower part of movable arm. While the underwriter's rules do not require a speed con- troller to be automatic, still it is good practice to make them so, as the same principles apply to the starting of a motor with a speed controller as with a starting box. Figure 36 shows a circuit breaker which is operative during the starting of the motor, and can be used to take the place of the switch required. As the arm of a starting box or speed controller is moved from one contact to another, more or less sparking results, and, as has already been stated, considerable heat is developed in the coils. A rheostat should never be located in a room where either inflammable gases or dust exist. If a starting box is to be located in a room where considerable dirt is apt to gather, or if the room is unusually damp, the starting box should be mounted in a dust-tight fire-proof box, which should -en a Figure 37 be kept closed at all times, except when starting the motor. If the enclosing box is rather large, sufficient ventilation of the coils will be obtained while the motor is being started and the door open. A speed controller should never be mounted in an enclosure unless the same is arranged to give a thorough ventilation to the outside air, as heat is constantly being gen- erated in the coils of the rheostat, and this heat must be dis- 74 MODERN ELECTRICAL CONSTRUCTION. sipated. A speed controller should never be located where dust or lint is apt to gather on it. If it is necessary to use one on a motor located in such a place, it should be mounted outside the room. In metal working establishments or in any place where there is a liability of the contacts on the switches or the starting boxes being short-circuited, they should be enclosed or suitably protected. e. Must not be run in series-multiple or multiple-series, except on constant-potential systems, and then only by special permission of the Inspection Department having jurisdiction. Figure 37 shows a series-multiple, and Figure 38 a multiple- series system of wiring. /. Must be covered with a waterproof cover when not in Figure 38 use, and, if deemed necessary by the Inspection Department having jurisdiction, must be enclosed in an approved case. From the nature of the question the decision as to what is an approved case must be left to the Inspection Department having jurisdiction to determine in each instance. When it is necessary to locate a motor in the vicinity of combustibles or in wet or very dusty or dirty places, it is gen- erally advisable to surround it with a suitable enclosure. The sides of such enclosure should preferably be made largely of glass, so that the motor may be always plainly visible. This lessens the chance of its being neglected, and allows any derangement to be at once noticed. Under certain conditions it is found necessary to enclose motors in dust-tight enclosures. The practice of building a small box which fits entirely around the motor, enclosing the MOTORS 75 pulley and provided with slots through which the belt passes, is very unsatisfactory. While this construction prevents con- siderable dust from settling on and around the motor, still a great deal will be carried in by the belt. If the box is so made that it fits tightly around the shaft between the pulley and the motor frame and is otherwise well constructed, most of the dust and dirt can be kept out. As the efficient working of the motor requires that it be kept as cool as possible, the box should afford sufficient ventilation. This may be obtained by making the box somewhat larger than the motor, thus allowing the heat to radiate from the sides, or the boxes should be ventilated to the outside air. A number of motors are so constructed that, by means of hand plates, they can be entirely enclosed. When they are so enclosed their efficiency and capacities are somewhat reduced, but cases are sometimes found where the conditions require motors of this kind to be used. In places where there is considerable dust flying about in the air, and where the dust is not readily combustible, a fine gauze can be used to close the hand holes. This gauze will allow ventilation, but will prevent the dirt from gathering inside the motor. The alternating induction motors, which are operated without brushes or collector rings, can be used in almost any location, as there is no sparking. g. Must, when combined with ceiling fans, be hung from insulated hooks, or else there must be an insulator interposed between the motor and its support. Ceiling fans are generally provided with an insulating knob on which the fan hangs. If this is not provided, a simple knob break can be used, or the fan can be suspended from a hook screwed into a hardwood block, provided the hook does not pass through the block into the plaster, the block being sep- arately supported from the ceiling. h. Must each be provided with a name-plate, giving the 76 MODERN ELECTRICAL CONSTRUCTION. maker's name, the capacity in volts and amperes, and the nor- mal speed in revolutions per minute. 9. Railway Power Plants. a. Each feed wire before it leaves the station must be equipped with an approved automatic circuit-breaker (see No. 52) or other device, which will immediately cut off the current in case of an accidental ground. This device must be mounted on a fireproof base, and in full view and reach of the attendant. 10. Storage or Primary Batteries. a. When current for light and power is taken from primary or secondary batteries, the same general regulations must be observed as apply to similar apparatus fed from dynamo gen- erators developing the same difference of potential. b. Storage battery rooms must be thoroughly ventilated. c. Special attention is directed to the rules for wiring in rooms where acid fumes exist (see No. 24, i to &). d. All secondary batteries must be mounted on non-absorp- tive, non-combustible insulators, such as glass or thoroughly vitrified and glazed porcelain. e. The use of any metal liable to corrosion must be avoided in cell connections of secondary batteries. Rubber-covered wire run on glass knobs should be used for wiring storage battery rooms. The knobs should be of such size as to keep the wire at least one inch from the surface wired over, and they should be separated 2y 2 inches for voltage up to 300, and 4 inches for voltages over 300. Waterproof sockets hung from stranded rubber covered wire and properly sup- ported independently of the joints should be used ; these lights to be controlled by a switch placed outside of battery room. All joints after being properly soldered and taped with both rubber and friction tape should be painted with some good insulating compound. This tends to keep all acid fumes away from the wire. TRANSFORMERS 77 11. Transformers. (For construction rules, see No. 62.) (See also Nos. 13, 130, 36.) a. In central or sub-stations the transformers must be so placed that smoke from the burning out of the coils or the boiling over of the oil (where oil filled cases are used) could do no harm. If the insulation in a transformer breaks down, consider- ble heat is likely to be developed. This would cause a dense smoke, which might be mistaken for a fire and result in water being thrown into the building, and a heavy loss there- by entailed. Moreover, with oil cooled transformers, espe- cially if the cases are filled too full, the oil may become ignited and boil over, producing a very stubborn fire. NOTICE-DO NOT FAIL TO SEE WHETHER ANY RULE OR ORDINANCE OF YOUR CITY CON- FLICTS WITH THESE RULES. CLASS B. OUTSIDE WORK. All Systems and Voltages. 12. Wires. a. Service wires must have an approved rubber insulating covering (see No. 41). Line wires, other than services, must have an approved weatherproof or rubber insulating covering (see Nos. 41 and 44). All tie wires must have an insulation equal to that of the conductors they confine. In risks having private generating plants, the yard wires running from building to building are not generally consid- ered as service wires, so that rubber insulation would not be required. By service wires are meant those wires which enter the building. It is customary to run the rubber-covered wire from the service switch and cutout inside of building through the outer walls, and to leave but a few feet of wire to which the line wires can later be spliced. This is illustrated in Figure 39, which shows how wires are run from pole to building. b. Must be so placed that moisture cannot form a cross connection between them, not less than a foot apart, and not in contact with any substance other than their insulating sup- ports. Wooden blocks to which insulators are attached must be covered over their entire surface with at least two coats of waterproof paint. c. Must be at least 7 feet above the highest point of flat roofs, and at least one foot above the ridge of pitched roofs over which they pass or to which they are attached. Roof structures are frequently found which are too low or much too light for the work, or which have been carelessly OUTSIDE WORK 79 put up. A structure which is to hold the wires a proper distance above the roof in all kinds of weather must not only be of sufficient, height, but must be substantially constructed of strong material It is well to avoid fastening wires perpendicular above one another, as in winter icicles may form which extend from the top to the lower wire, and the moisture on these will often Figure 39 cause much trouble. The rule requires that wires be 7 feet above flat roofs, and roof structures must, therefore, be made high enough to allow for "sag." In moderately long runs 2 or 3 feet will be sufficient. For long runs, see following table, taken from construction rules of Commonwealth Electric Com- pany of Chicago : The tension on wires should be such that the sag of a span of 125 feet will not exceed the amounts shown. Temperature, F...10 20 30 40 50 60 70 80 90 Sag, feet 6 8 8 10 10 12 12 14 14 This table will also be useful to consult when running wires over housetops to which they are not attached, as it shows the variation in "sag" due to different temperatures. Wires MODERN ELECTRICAL CONSTRUCTION. should be so run that even at the highest temperature they will still clear the buildings. Allowance should also be made for the gradual elongation of the wire due to its own weight, giving way of supports or sleet that may at times weigh it down. d. Must be protected by dead insulated guard irons or wires from possibility of contact with other conducting wires or substances to which current may leak. Special precautions of this kind must be taken where sharp angles occur, or where any wires might possibly come in contact with electric light or power wires. Crosses, when unavoidable, should be made as nearly at right angles as possible. These guard wires are run parallel to and above the lower set of wires. Their object is to prevent the upper crossing wires, should they break, from coming in contact with the lower. A separate set of cross arms must be placed on the lower poles or above the lower wires to which the guard wires must be fastened. In Figure 40 1 and 2 show break in- sulators that may be used to electrically disconnect guard wires. e. Must be provided with petticoat insulators of glass or porcelain. Porcelain knobs or cleats and rubber hooks will not be approved. /. Must be so spliced or joined as to be both mechanically and electrically secure without solder. The joints must then be soldered, to insure preservation, and covered with an insulation equal to that on the conductors. All joints must be soldered, even if made with some form of patent splicing device. This ruling applies to joints and splices in all classes of wiring covered by these rules. In Figure 40 single and double petticoat insulators are shown. It is very often convenient to fasten such insulators upside down or horizontally, but this should never be done, as they will then fill with water or dirt and their insulating qualities be destroyed. g. Must, where they enter buildings, have drip loops outside, and the holes through which the conductors pass must OUTSIDE WORK 81 be bushed with non-combustible, non-absorptive insuh ting tubes slanting upward toward the inside. 7i. Telegraph, telephone and similar wires must not be placed on the same cross-arm with electric light or power wires, and when placed on the same pole with such wires the distance between the two inside pins of each cross-arm must not be less than 26 inches. i. The metallic sheaths to cables must be permanently and effectively connected to "earth." The telephone or telegraph wires are sometimes placed above the power wires, and it very often becomes necessary Figure 40 for a lineman to pass through the lower wires to get at the tipper. Great care is necessary to avoid coming in contact with high tension power wires while handling the telephone wires. Poles should not be set more than 125 feet apart ; 100 or 110 feet is good practice. For small wires poles with 6-inch tops are often used, but for heavier wires 7-inch tops are advisable. The tops of pole should be pointed, so as to shed water, and the whole pole be well painted. Steps should be placed so that the distance between any two steps on the same side is not over 36 inches ; these steps should all be the same distance apart, and should not extend nearer than 8 feet to the ground. All "gains" cut into poles should be painted before cross-arms are placed in them. Such places are more 82 MODERN ELECTRICAL CONSTRUCTION. likely to hold moisture and rot than exposed parts. Wherever feed wires end or sharp angles occur, double cross-arms should be used, fastened on opposite sides of pole and bolted together. All bolts, lag screws, etc., should be galvanized. Poles should be set at least as far into the ground as shown in the following table : Length of pole. . Depth in ground. 35 feet S 1 /, feet 40 " 6 45 " 6 50 " 6y 2 " 55 " 7 60 " 8 The holes should be large enough to admit of thorough tamping on all sides of bottom of hole. If the tamping at bottom of hole is not well done, the pole will always be shaky, no matter how much tamping may be done at the top. If the ground is soft, the pole may be set in cement, or short pieces of planking fastened to it at right angles underground. At the end of line or where sharp bends occur, strong gal- vanized guy cables fastened to poles six or eight feet long, buried underground, should be used. Trolley Wires. /. Must not be smaller than No. B. & S. gage copper or No. 4 B. & S. gauge silicon bronze, and must readily stand the strain put upon them when in use. k. Must have a double insulation from the ground. In wooden pole construction the pole will be considered as one insulation. /. Must be capable of being disconnected at the power plant, or of being divided into sections, so that, in case of fire on the railway route, the current may be shut off from the OUTSIDE WORK 83 particular section and not interfere with the work of the firemen. This rule also applies to feeders. m. Must be safely protected against accidental contact where crossed by other conductors. Guard wires should be insulated from the ground and should be electrically disconnected in sections of not more than 300 feet in length. Ground Return Wires. . For the diminution of electrolytic corrosion of under- ground metal work, ground return wires must be so arranged that the difference of potential between the grounded dynamo terminal and any point on the return circuit will not exceed twenty-five volts. It is suggested that the positive pole of the dynamo be connected to the trolley line, and that whenever pipes or other underground metal work are found to be electric-ally positive to the rails or surrounding earth, that they be connected by conductors arranged so as to prevent as far as possible cur- rent flow from the pipes into the ground. 12 A. Constant-Potential Pole Lines, Over 5,000 Volts. (Overhead lines of this class unless properly arranged may increase the fire loss from the following causes : Accidental crosses between such lines and low-potential lines may allow the high-voltage current to enter buildings over a large section of adjoining country. Moreover, such high voltage lines, if carried close to buildings, hamper the work of firemen in case of fire in the building. The object of these rules is so to direct this class of construction that no increase in fire hazard will result, while at the same time care has been taken to avoid restrictions which would un- reasonably impede progress in electrical development. It is fully understood that it is impossible to frame rules which will cover all conceivable cases that may arise in con- struction work of such an extended and varied nature, and it is advised that the Inspection Department having jurisdiction be freely consulted as to any modification of the rules in par- ticular cases.) a. Every reasonable precaution must be taken in ar- 84 MODERN ELECTRICAL CONSTRUCTION. ranging routes so as to avoid exposure to contacts with other electric circuits. On existing lines, where there is a liability to contact, the route should be changed by mutual agreement between the parties in interest wherever possible. b. Such lines should not approach other pole lines nearer than a distance equal to the height of the taller pole line, and such lines should not be on the same poles with other wires, except that signalling wires used by the Company operating the high-pressure system, and which do not enter property other than that owned or occupied by such Com- pany, may be carried over the same poles. c. Where such lines must necessarily be carried nearer to other pole lines than is specified in Section b above, or where they must necessarily be carried on the same poles with other wires, extra precautions to reduce the liability of a breakdown to a minimum must be taken, such as the use of wires of ample mechanical strength, widely spaced cross-arms, short spans, double or extra heavy cross-arms, extra heavy pins, insulators, and poles thoroughly supported. If carried on the same poles with other wires, the high-pressure wires must be carried at least three feet above the other wires. d. Where such lines cross other lines, the poles of both lines must be of heavy and substantial construction. Whenever it is feasible, end-insulator guards should be placed on the cross-arms of the upper line. If the high- pressure wires cross below the other lines, the wires of the upper line should be dead-ended at each end of the span to double-grooved, or to standard transposition insulators, and the line completed by loops. One of the following forms of construction must then be adopted : 1. The height and length of the cross-over span may be made such that the shortest distance between the lower cross-arms of the upper line and any wire of the lower line will be greater than the length of the cross-over span, so that a wire breaking near one of the upper pins would not be long enough to reach any wire of the lower line. The high-pressure wires should preferably be above the other wires. OUTSIDE WORK 85 2. A joint pole may be erected at the crossing point, high-pressure wires being supported on this pole at least three feet above the other wires. Mechan- ical guards or supports must then be provided, so that in case of the breaking of any upper wire, it will be impossible for it to come into contact with any of the lower wires. Such liability of contact may be prevented by the use of suspension wires, similar to those em- ployed for suspending aerial telephone cables, which will prevent the high-pressure wires from falling in case they break. The suspension wires should be supported on high-potential insulators, should have ample mechanical strength, and should be carried over the high-pressure wires for one span on each side of the joint pole, or where suspension wires are not desired guard wires may be carried above and below the lower wires for one span on each side of the joint pole, and so spread that a falling high-pressure wire would be held out of contact with the lower wires Such guard wires should be supported on high- potential insulators or should be grounded. When grounded, they must be of such size, and so con- nected and earthed, that they can surely carry to ground any current which may be delivered by any of the high-pressure wires. Further, the construc- tion must be such that the guard wires will not be destroyed by any arcing at the point of contact likely to occur under the conditions existing. 3. Whenever neither of the above methods is feasible, a screen of wires should be interposed between the lines at the cross-over. This screen should be supported on high tension insulators or grounded and should be of such construction and strength as to prevent the upper wires from coming into contact with the lower ones. If the screen is grounded each wire of the screen must be of such size and so connected and earthed that it can surely carry to ground any current which may be delivered by any of the high pressure wires. Further, the construction must be such that the wires of screen will not be destroyed by any arcing at the point of contact likely to occur under the conditions existing. e. When it is necessary to carry such lines near buildings, they must be at such height and distance from the building as not to interfere with firemen in event of fire; therefore, if 86 MCDEIIN ELZCTr.ICAL CONSTRUCTION. wi'.hin 25 feet of a building, they irvst be carried at a height ret less lhan that of the front cornice, a::d the height must be greater than that of the cornice, as the wires come nearer to the building, in accordance with the following table : Distance of wire Elevation of wire from building. above cornice of building. Feet. Feet. 25 20 2 15 4 10 6 5 8 2% 9 Tt Is evident that where the roof of the building continues nearly in line with the walls, as in Mansard roofs, the height and distance of the line must be reckoned from some part of the roof instead of from the cornice. 13. Transformers. (For construction rules, see No. 62.) (See also Nos. n, 13 A and 36.) Where transformers are to be connected to high-voltage circuits, it is necessary in many cases, for best protection to life and property, that the secondary system be permanently f rounded, and provision should be made for it when the trans- ormers are built. a. Must not be placed inside of any building excepting central stations, unless by special permission of the Inspection Department having jurisdiction. An outside location is always preferable; first, because It keeps the high-voltage primary wires entirely out of the building, and second, for the reasons given in the note to No. 11 a. b. Must not be attached to the outside walls of buildings, unless separated therefrom by substantial supports. The alternating current transformer consists of an iron core upon which wires of two distinct electrical circuits are wound. One of these is known as the primary circuit, and in it the high pressure currents coming direct from the dynamo circulate. The other is known as the secondary circuit, and in it the low pressure currents used inside of buildings circu- GROUNDING 87 late. These two circuits are wound generally one over the other, and are very close together. The pressure used in the primary coil is from 1,000 to 5,000 volts, while in the secondary it is reduced usually to 110 or 220. It quite frequently happens that the insulation between the two windings breaks down and thus the high pressure is acci- dentally brought into buildings. Under such circumstances should any one touch any live part of the installation while touching also grounded parts of the building death would very likely result. Also, should there be a weak spot in the insula- tion, it is quite likely the high pressure would pierce it at that point with a possible result of a fire. Many deaths and fires Figure 41 have been caused in this way. If such lines are connected to ground the chances for harm are very much lessened, for the current will never take the path of high resistance through a man's body, while a direct path through a low resistance wire is open to it. It must not be supposed that "grounding" one side of an electric light system is not often followed by serious conse- 88 MODERN ELECTRICAL CONSTRUCTION. quences, for under such circumstances a ground coming on any other part of the system will cause a short circuit at once. The grounding in these cases is to be looked upon as the lesser of two evils rather than as an advantage. With alternating currents, the chances of possible damage from grounding are much less than with direct currents, because each trans- former with its small group of lamps is a system by itself and not affected by grounds on other transformers. Thus a 5,000 light alternating current installation would consist of from 25 to 50 separate systems, each independent of defects on the rest, while in a continuous current installation, a ground on the most remote branch circuit would in conjunction with a ground on the opposite pole of any other part of the system form a short circuit. Methods of grounding secondary wires of alternating cur- rent transformers are shown in Figure 41, taken from an instruction book issued by the Commonwealth Electric Com- pany of Chicago. In connection with 3-wire systems, grounding of the neutral wire can do little harm, because ordinarily the neutral wire seldom carries much current, and that current is apt to vary in direction so that the electrolytic effect will be on the whole quite negligible. There is, of course, the hazard brought about by the fact that a ground coming on one of the outside wires will imme- diately form a short-circuit in connection with the ground on the neutral. In connection with 3-wire systems, however, it is of the greatest importance (as more fully explained further on) that the neutral wire remain intact, and it being thoroughly grounded at all available outside places will help to keep it so. 13 A. Grounding Low-Potential Circuits. The grounding of low-potential circuits under the follow- GROUNDING. 89 Ing regulations Is only allowed when such circuits are so ar- ranged that under normal conditons of service there will be no passage of current over the ground wire. Direct-Current 3-Wire System. a. Neutral wire may be grounded, and when grounded the following rules must be complied with : 1. Must be grounded at the Central Station on a metal plate buried in coke beneath permanent moisture level, and also through all available underground water and gas-pipe systems. 2. In underground systems the neutral wire must also be grounded at each distributing box through the box. 3. In overhead systems the neutral wire must be grounded every 500 feet, as provided in Sections c, c, f and g. Inspection Department having jurisdiction may require grounding if they deem It necessary. Two-wire direct-current systems having no accessible neu- tral point are not to be grCunded. Alternating-Current Secondary Systems. b. Transformer secondaries of distributing systems should preferably be grounded, and when grounded, the follow- ing rules must be complied with : 1. The grounding must be made at the neutral point or wire, whenever a neutral point or wire is accessible. 2. When no neutral point or wire is accessible, one side of the secondary circuit may be grounded, pro- vided the maximum difference of potential between the grounded point and any other point in the circuit does not exceed 250 volts. 3. The ground connection must be at the transformer as provided in sections d, c, f, g, and when trans- formers feed systems with a neutral wire, the neu- tral wire must also be grounded at least every 250 feet for overhead systems, and every 500 feet for underground systems. Inspection Departments having jurisdiction may require grounding if they deem it necessary. 90 MODERN ELECTRICAL CONSTRUCTION. Ground Connection. c. The ground wire in direct-current 3-wire systems must not at Central Stations be smaller than the neutral wire and not smaller than No. 6 B. & S. gage elsewhere. d. The ground wire in alternating-current systems must never be less than No. 6 B. & S. gage, and must always have equal carrying capacity to the secondary lead of the trans- former, or the combined leads where transformers are con- nected in parallel. On three phase systems, the ground wire must have a carrying capacity equal to that of any one of the three mains. c. The ground wire must be kept outside of buildings, but may be directly attached to the building or pole. The wire must be carried in as nearly a straight line as possible, and kinks, coils and sharp bends must be avoided. /. The ground connection for Central Stations, trans- former substations, and banks of transformers must be made through metal plates buried in coke below permanent mois- ture level, and connection should also be made to all available underground piping systems including the lead sheath of under- ground cables. g. For individual transformers and building services the ground connection may be made as in Section f, or may be made to water or other piping systems running into the build- ings. This connection may be made by carrying the ground wire into the cellar and connecting on the street side of meters, main cocks, etc., but connection must never be made to any lead pipes which form part of gas services. In connecting a ground wire to a piping system, the wire should, if possible, be soldered into a brass plug and the plug forcibly screwed into a pipe-fitting, or, where the pipes are cast iron, into a hole tapped into the pipe itself. For large stations, where connecting to underground pipes with bell and spigot joints, it is well to connect to several lengths, as the pipe joints may be of rather high resistance. Where plugs cannot be used, the surface of the pipe may be filed or scraped bright, the wire wound around it, and a strong clamp put over the wire and firmly bolted together. Where ground plates are used, a No. 16 Stubbs' gage copper plate, about three by six feet in size, with about two feet of crushed coke or charcoal, about pea size, both under ana over it, would make a ground of sufficient capacity for a GROUND PLATES. 91 moderate-sized station, and would probably answer for the ordinary substation or bank of transformers. For a large central station, a plate with considerably more area might be necessary, depending upon the other underground con- nections available. The ground wire should be riveted to the plate in a number of places, and soldered for its whole length. Perhaps even better than a copper plate is a cast- iron plate with projecting forks, the idea of the fork being to distribute the connection to the ground over a fairly broad area, and to give a large surface contact. The ground wire can probably best be connected to such a cast-iron plate by soldering it into brass plugs screwed into holes tapped in the plate. In all cases, the joint between the plate and the ground wire should be thoroughly protected against corrosion by painting it with waterproof paint or some equivalent. NOTE.-DO NOT FAIL TO SEE WHETHER ANY RULE OR ORDINANCE OF YOUR CITY CONFLICTS WITH THESE RULES. CLASS C. INSIDE WORK. All Systems and Voltages. GENERAL RULES. 14. Wires. (For special rules, see Nos. 18, 24, 35, 38 and 39.) a. Must not be of smaller size than No. 14 B. & S. gage, except as allowed under Nos. 24 v and 45b. The exceptions being wires used inside of fixtures and flexible cord used to suspend individual electric lights. For general purposes a wire smaller than No. 14 is too easily broken, either through a sharp kink, or by drawing too tight with tie wires. To avoid trouble from kinks or sharp bends, wires smaller than 14 should preferably be stranded. b. Tie wires must have an insulation equal to that of the conductors they confine. This is considered necessary, because very often the tie wire cuts through the insulation of the wire it confines, and if the tie wire should come in contact with other than its insu- lating support, there would still be good insulation. In Figure 42, (1) and (2) illustrate the method of tieing usually employed with small wires on insulators ; (4) shows a method employed with larger wires. This is also especially useful, because slack can be taken up if the tie wire is arranged to draw the main wire about half way around the insulator; (6) shows a knot tied into the wire, as is usual where the end of the wire INSIDE WORK. 93 connects into cut-outs or switches. At (5) insulators are arranged to hold large wires. It is not advisable to tie large wires to insulators, as the weight of the wire will soon cause Figure 42 Cleats, such as shown at (8) it to cut through the insulation, and (9), are preferable. c. Must be so spliced or joined as to be both mechanically and electrically secure without solder. The joints must then 94 MODERN ELECTRICAL CONSTRUCTION. C Figure 43 INSIDE WORK. 95 be soldered to insure preservation, and covered with an insu- lation equal to that on the conductors. Stranded wires must be soldered before being fastened under clamps or binding screws, and whether stranded or solid, when they have a conductivity greater than that of No. 8 B. & S. gage they must be soldered into lugs for all terminal connections. All joints must be soldered, even if made with some form of patent splicing device. This ruling applies to joints and splices in all classes of wiring covered by these rules. At the left on top of Fig. 43 is shown the well-known Western Union joint. Before joining wires they should be thoroughly cleaned by scraping with the back of a knife or sand or emery paper. The insulation should be removed, as indicated at b; if it is cut into as at a, it is very likely that the wire will be "nicked" and will be likely to break at that point. It is also more difficult to tape a joint properly if the rubber has been cut in this way than it is with the rubber cut as at b. After the joint has been made it is covered with soldering fluid, a formula for which is given below. In lieu of this there are soldering sticks and salts, already prepared, on the market. The following formula for soldering fluid is sug- gested : Saturated solution of zinc chloride 5 parts Alcohol 4 parts Glycerine 1 part The joint having been thoroughly covered with one of these preparations is next heated with a gasoline or alcohol torch and a small piece of solder allowed to melt on it near the center. It is well to avoid heating too much at the ends of the joint, as it weakens the wire. After the joint is cool, wipe off all moisture and cover with layers of rubber tape, enough, at least, so that it is equal in thickness to the rubber insulation on the wire used, as shown at a and b. This rubber 96 MODERN ELECTRICAL CONSTRUCTION. tape is then covered with friction tape to keep it in place. Before taping joints the outer braid of the wire should be carefully skinned back. If any of the cotton threads of which it consists were to be left in contact with the bare wire, they would, when moist, form a leak, which might prove trouble- some. If joints are exposed to the weather it will be well to paint them over with some insulating paint to keep the friction tape in place, as it will otherwise soon work loose when it becomes dry. At c and d "tap" joints are shown. The method shown at d is preferable, because the wire cannot easily work loose. The method of joining shown at c is useful when, for instance, two wires, each of which is fastened to an insulator, are to be joined. The wires c?n be drawn very tight in this way. This sort of joint is very common in fixture work, and should be finished off as at f. Twin wires other than flexible cord are allowed only in metal conduits, and joints in them should be made only within the junction boxes. When joints in conduit are unavoidable, twin wires should be joined as at g, so that the joints are not opposite each other. Joints in flexible cord should be avoided as much as possible. In splicing stranded wires it is customary to remove some of the center strands to avoid making a very bulky splice. All stranded wires must be soldered where fastened under binding screws; this refers also to flexible cord used in sockets. The best way to solder the ends of cords is to dip them in melted solder; a blow torch will easily overheat small wires and leave them brittle. Figure 44 shows lead covered wire spliced and taped. In handling lead covered wire great care must be exercised (especially with paper insulated) that it be not bruised and the lead not punctured. The lead covering is of use only as a protection against water; if it admits the least bit of moisture INSIDE WORK. 97 it is worse than useless. The ends of lead covered wires should always be kept sealed until ready for use; in damp places the paper insulation may absorb moisture, which will ground the wire on the lead. When installed the ends should always be sealed against moisture. Lead covered wires should never be used where there is a liability of nails being driven into them. Joints in lead covered wires are made just as in ordinary wires. Extreme care is necessary that no moisture be left on Figure 44 the wire when it is taped or covered up. Before the wire is joined a sleeve (Figure 44) is slipped over one of the wires. After the joint has been made and taped, this sleeve is placed so as to cover it, and the ends split and arranged to fit close against the lead on the wires. That part of the lead which must be soldered to make the joint watertight is scraped until it is perfectly bright and then coated with tallow candle grease. It can then be soldered with an iron, or melted solder can be poured on it and wiped around it, as plumbers do. If a soldering iron is used it must not be too hot, and not allowed to remain in one place too long, as the lead itself melts at nearly the same temperature as the solder. An inexperienced workman may burn more holes into the lead than he closes. If a neat job is desired, that part of the lead which is to be kept free of solder is covered with lampblack and glue, or ordinary paper hanger's paste, or a mixture of flour and water boiled, so as to prevent the solder from taking on it. d. Must be separated from contact with walls, floors, timbers or partitions through which they may pass by non- 98 MODERN ELECTRICAL CONSTRUCTION. combustible, non-absorptive insulating tubes, such as glass or porcelain, except as provided in No. 24 . Bushings must be long enough to bush the entire length of the hole in one continuous piece or else the hole must first be bushed by a continuous waterproof tube. This tube may be a conductor, such as iron pipe, but in that case an insulating bushing must be pushed into each end of It, ex- tending far enough to keep the wire absolutely out of contact with the pipe. The exception mentioned is in regard to wires at outlets where they are required to be in approved flexible tubing from the last insulator to at least one inch beyond plaster, or end of the cap on gas piping. This is shown in Figure 45. The reason for the separation of wires from everything but their insulating supports are many. Should a bare live wire come in contact with damp woodwork or masonry, there would Figure 45 very likely be some flow of current to ground and through the ground to the other pole of the dynamo or other wire. This flow of current may gradually char the woodwork, and in time start a fire ; or it may gradually eat away the wire, finally causing it to break. When a wire is eaten away, as shown INSIDE WORK. 99 at c and e, Figure 46, if it is carrying much current, the thin part will become very hot and will set fire to whatever inflam- mable material may be near it. If the current flow to the ground continues, the positive wire will finally be entirely severed, and an arc, similar to that noticed in an ordinary arc lamp, will be established, and will continue until the wire has Figure been burned away and the space between the two ends becomes too great for the arc to maintain itself. The negative wire, to which the current flows, is not eaten away in this manner, and such current flow is only possible when two wires of a system are in electrical connection with the ground. This action may, however, occur, even if the two grounded wires are miles apart. Wires and gas pipes are often destroyed through intermittent contact; for instance, if a wire makes a good contact to a gas pipe and there is a small leak to the pipe no particular harm will be done as long as the contact remains good. Should, however, the contact be intermittent, there will be a small arc at each break, and this will, little by little, burn holes into the gas pipe and into the wire. This action will take place on either a positive or negative wire. Non-com- 100 MODERN ELECTRICAL CONSTRUCTION. bttstible supports for wires are farther useful in that they tend to prevent flames from the rubber insulation (which is very easily ignited from any of the above causes) from spread- ing to surrounding material. Figure 46 consists of copies of specimens showing effects of electrolysis, short circuits, and heating of lamp. These illustrations are copied from fire reports of the National Board of Underwriters. At a is shown a piece of gas pipe, which had been subject to electrolytic action until finally a hole had been eaten through the metal ; b is a socket which had been short cir- cuited, and the excessive damage was due to overfusing ot circuit. At c and e, the effects of electrolysis on wire are shown ; c is a piece of underwriter's wire (not approved in moulding), which had been used in damp moulding, the leak to ground through the dampness causing the gradual eating. away of the wire; c shows a breakdown in the insulation and subsequent electrolytic action on the wire, causing it finally to break. This wire had been used in a round-house, where the sulphur fumes and the condensation of escaping steam on insulators had formed a path to ground. At d is an incandescent lamp which had been covered with a towel, the confined heat soft- ening the glass and setting fire to the towel. The danger of fire from overheated lamps is much greater than is generally supposed. Small lamps and lamps subject to a little excess of voltage are especially dangerous, and many instances are on record where they have charred woodwork and set fire to cloth or paper shades. It may in many cases seem unnecessary to have bushings in one piece long enough to pass through a floor, or wide wall; but especially in passing through floors, it is very easily possible for wires to become crossed between the joists; that is, the wire entering at the right above the floor may be INSIDE WORK. 101 brought out at the left below the floor and the other wire through the opposite holes. In such a case the two wires of opposite polarity will be in contact, and should the insulation give out from any cause whatever, such as abrasion, or the gnawing of rats and mice, there would be nothing to prevent a short circuit and consequent fire. In passing through floors or walls the wires often come in contact with concealed pipes or other grounded material, so that only by making the bush- ings continuous can the wires be properly protected. Figure 48 shows short bushings arranged in iron pipe. Figure 49 shows a case where there is an offset in the wall. Cases of this kind very often occur. Sometimes the floor can be taken up and an iron conduit, properly bent, put in place ; or the wires placed on insulators. In this latter case the floor must not be put down until the inspector has examined the wires. The wires may be run on top of the floor to such a place where a continuous bushing may be dropped through Figure 47 Figure 48 Figure 49 the floor. The wires on top of the floor must be then pro- tected by a suitable boxing or at least the same dimensions as given for boxing on side walls. e. Must be kept free from contact with gas, water or other metallic piping, or any other conductors or conducting ma- 102 MODERN ELECTRICAL CONSTRUCTION. terial which they may cross, by some continuous and firmly fixed non-conductor, creating a separation of at least one inch. Deviations from this rule may sometimes be allowed by spe- cial permission. When one wire crosses another wire the best and usual means of separating them is by means of a porcelain tube on one of them. The tube should be prevented from moving out of place, either by a cleat at each end, or by taping it securely to the wire. The same method may be adopted where wires pass close to iron pipes, beams, etc., or, where the wires are above the pipes, as is generally the case, ample protection can frequently be secured by supporting the wires well with a porcelain cleat placed as nearly above the pipe as possible. Figure 50 is a sectional view of the manner in which wires are usually run through joists in bushings. For small wires bushings should preferably be installed as shown at top ; never as shown in the middle row. For larger wires the holes must Figure 50 be bored as straight as possible ; otherwise it will be difficult to pull wires through. The quantity of wire needed is also somewhat increased by slanting the holes. In open places wires are generally installed on insulators as shown in Fig- ure 51. Figure 51 shows different methods employed where one wire crosses another. The method at the left, which is more suited to large stiff wires, does not quite comply with the rule, but is very often used. The other two methods are preferable. Insulating supports should always be provided at the place of crossing to prevent the upper wires from sagging and resting on the lower; also to prevent any strain from coming on tap joints. Approved flexible tubing such as circular loom IXSIDE WORK. 103 is also often used in crossing wires and pipes. In dry loca- tions it is quite safe and does not break as easily as tubes, but should never be used where there is any likelihood of dampness. f. Must be so placed in wet places that an air space will be left between conductors and pipes in crossing, and the Figure 51 former must be run in such a way that they cannot come in contact with the pipe accidentally. Wires should be run over rather than under pipes upon which moisture is likely to gather or which, by leaking, might cause trouble on a circuit. This is a rule that is very often violated, as much work is done using loom, as shown at the left of Figure 52, and is quite safe with gas pipes. With cold water pipes, which are Figure 52 likely to sweat, or with steam pipes, it is very bad practice. Where pipes are close against a ceiling it is better either to fish over them or drop wires some distance below them as 104 MODERN ELECTRICAL CONSTRUCTION. illustrated at the right of the figure. No part of the wiring should be in contact with pipes. On side walls where ver- tical wires run across horizontal pipes the only safeguard would be to box the pipes and run the moisture to one side. The most harm is done by water on the insulators. If these can be kept dry it does not matter much about wires which hang free in the air. Whatever form of insulation is used in crossing pipes, it must be continuous. Short bushings strung on the wire, where a large pipe or number of pipes are being crossed, is not satisfactory, as the bushings are apt to separate or moisture gather in the space between them. The insulation must also be firmly attached to the wires. If knobs are not used as shown in Figure 51 to keep the bush- ings in place, they must be taped to the wire. g. The installation of electrical conductors in wooden moulding or where supported on insulators in elevator shafts will not be approved, but conductors may be installed in such shafts if encased in approved metal conduits. Wires supported on insulators in such places are very likely to be disturbed, especially in freight elevators. Moulding is often so impregnated with oil, and the draft in an elevator shaft is usually so strong that a blaze once started would quickly run to the top. 15. Underground Conductors. a. Must be protected against moisture and mechanical injury where brought into a building, and all combustible material must be kept from the immediate vicinity. b. Must not be so arranged as to shunt the current through a building around any catch-box. By reference to Figure 53 the meaning of this rule will be made clear. With wires run as shown it would be easy for any one having disconnected one service switch to believe all wires in the building dead, while they were in reality still being kept alive by the other switch. INSIDE WORK. 105 c. Where underground service enters building through tubes, the tubes shall be tightly closed at outlets with asphalt- urn or other non-conductor, to prevent gases from entering the building through such channels. d. No underground service from a subway to a building shall supply more than one building except by written permis- sion from the Inspection Department having jurisdiction. 17. Switches, Cut-Outs, Circuit-Breakers, Etc. (For construction rules sec Nos. 51, 52 and 53.) a. Must, unless otherwise provided (for exceptions, see No. 8 c and No. 22 c), be so arranged that the cut-outs will protect, and the opening of a switch or circuit-breaker will \ _ ^ I i fiS** Figure 53 disconnect, all of the wires ; that is, in a two-wire system the two wires, and in a three-wire system the three wires, must be protected by the cut-out and disconnected by the operation of the switch or circuit breaker. The exceptions are in regard to motors of l /4 H. P. or less on circuits of not over 300 volts and incandescent cir- cuits of not over 660 watts where single pole switches are allowed. This rule forbids the practice, as sometimes em- 106 MODERN ELECTRICAL CONSTRUCTION. ployed on switchboards, of breaking the two outside wires of a 3-wire system and leaving the neutral, which is not carried through the switch, always connected. . . In connecting double-pole snap switches the wireman should be very careful. Most of these switches cross polari- ties as shown in Figure 54, and if connected wrong will form short circuits. Many of them have been connected that way, even by wiremen of some experience. b. Must not be placed in the immediate vicinity of easily ignitable stuff or where exposed to inflammable gases or dust or to flyings of combustible material. In starch and candy factories, grain elevators, flouring mills, and buildings used for woodworking or other purposes which would cause the fittings to be exposed to dust and flyings of inflammable material, the cut-outs and switches should be placed in approved cabinets outside of the dust-rooms. If, however, it is necessary to locate them in the dust-rooms, the cabinets must be dust-proof and must be provided with self- closing doors. Whenever an electric current is broken, whether by fuse or switch, an arc varying with the current strength, is Figure 54 Figure 55 Figure 56 formed. Should a switch be only partly opened, this arc will continue and consume the metal of the switch until the gap in which it burns becomes too long, when the current will be broken. Meanwhile there is much heat generated INSIDE WORK. 107 which may readily communicate to inflammable material nearby. There seems to be no reason except economy of wire why cut-outs should ever be placed inside of dust rooms. Switches of course must often be placed in such rooms as in many cases the entire building outside of the engine room is dusty. In such cases the switches as well as the cutouts may, how- ever, be often placed on the outside walls convenient to some window. An approved cabinet is shown in Figure 55. If used in connection with knife switches it should be large enough to admit being closed when the switch is open. In cases where cut-outs and switches must be located in dusty rooms, it would be well to construct double cabinets, one part for the cut-outs and another for the switches. The fuses, which are the most dangerous can then be tightly enclosed, as it will seldom be necessary to get at them. In practice it has been found almost impossible to keep the doors of cabinets which are much used closed. It seems next to impossible to con- struct a cabinet which is dust proof, with a door that can be readily opened, and a self-closing door can hardly be made to remain dustproof. Doors are made self-closing either through gravity or by suitable springs. As switch and cut-out boxes are very likely to be used for the storage of cotton waste, paper, etc., which would readily ignite from a melted fuse, it would be well to construct them with a slanting bottom as indicated by the dotted line in Fig- ure 56, so that nothing will lie in them. c. Must, when exposed to dampness, either be enclosed in a waterproof box or mounted on porcelain knobs. Figure 56 is a sectional side view of a cut-out box for use out of doors. In it the switch is mounted on porcelain knobs. In all damp places much trouble is experienced from leakage through the moisture on the surface of the slate or marble 108 MODERN ELECTRICAL CONSTRUCTION. and through the wax used to cover the bare parts on back of switch. d. Time switches must be enclosed in an iron box or cabinet lined with fire resisting material. If an iron box is used, the minimum thickness of the iron must be 0.128 cf an inch (No. 8 B. & S. Gauge). If the cabinet is used, it must be lined with marble or slate at least % of an inch thick, or with iron not less than 0.128 of an inch thick. Box or cabinet must be so constructed that when switch operates blade shall clear the door by at least one inch. CONSTANT-CURRENT SYSTEMS. PRINCIPALLY SERIES ARC LIGHTING. 18. Wires. (Sec also Nos. 14, 15 and 16.) a. Must have an approved rubber insulating covering (see No. 41). b. Must be arranged to enter and leave the building through an approved double-contact service switch (see No. 51 &), mounted in a non-combustible case, kept free from mois- ture, and easy of access to police or firemen. In order that all of the wiring in the building may be entirely disconnected a switch, the principle of which is illus- Figure 57 trated at d, Figure 57, is provided where wires enter and leave the building. A modern commercial form of this switch is shown in Figure 58. This switch never breaks the circuit. As shown in Figure 57, the current passes from the positive pole, through the upper blade of the switch to b and thence CONSTANT CURRENT SYSTEMS. 109 through the arc lamps back to c and to the negative pole. When it is desired to extinguish the lamps the two blades of the switch are moved downward, as indicated by the dotted lines. The contacts d are arranged so that both switch blades connect with them before disconnecting entirely from the points b and c. As soon as both blades are in contact with d all current flows through it because the resistance of it is so very much less than that of the lamps. With the switch in the position indicated by dotted lines, the current still flows in the outside wires, but all wires within the building are "dead." At c, Figure 57, is shown a single-pole switch which operates on the same principle as the other. If this switch is closed all current will pass through it ; if open the current will pass through the last lamp. A switch of this kind is always arranged within the lamp itself. This latter way of switching lamps should never' be used, as a lamp switched in this way is never safe to handle. There is just as much danger from shocks when the lamp is switched off as when on. With switches as de- scribed above there is no spark whatever when lamps are switched off, but there is usu- ally quite a spark when the lamps are switched in. Should there be a broken wire or a lamp out of order in the circuit to be switched in, there will be quite an arc maintained for some time. In such a case the switch should be quickly closed and the trouble located. Fig. 58. 110 MODERN ELECTRICAL CONSTRUCTION. In handling live wires of this system great care is neces- sary. The wireman should insulate himself from the ground by a dry board, or, if all about him is damp, by a board resting on insulators. Rubber gloves and rubber boots, if kept dry, are useful. Death or bad burns may result if the wireman, standing on wet ground or any conductor in connection with it, touches part of a circuit which is also partly in connection with the ground. If, in Figure 57, the wire at / is grounded, a man in connection with the ground and touching a bare wire at h will receive a shock due to about 50 volts, but if he touches the wire at g, he will receive a shock of about 150 volts. The shock received from a line containing 100 lamps may be any- thing from 50 to 5,000 volts, and may result in only a slight burn or in instant death. Another danger in connection with live circuits is the lia- bility of cutting oneself into circuit. If one is perfectly insulated from the ground there is no harm whatever in touch- ing one live wire (with very high voltages such insulation is, however, hard to obtain) with either one or both hands while the wires are in order. Should, however, the wire between the two hands break, the current would immediately pass through the body, very likely causing instant death. Even if the circuit is not entirely broken, if only a resistance is cut in, the shock will be very severe. As, for instance, if one should touch the terminal of an arc lamp, not burning, with each hand nothing whatever would be felt, but, if the lamp were now suddenly switched on, there would be a very severe shock at first, which would become less so when the lamps were fairly started. To avoid the possibility of such occurrences when working on live lamps or circuits a short wire known as a "jumper" is often connected, as at k, Figure 57. This will carry all current, and there is now no danger except from a connection to ground. CONSTANT CURRENT SYSTEMS. Ill c. Must always be in plain sight, and never encased, except when required by the Inspection Department having juris- diction. What is known as concealed knob and tube work is not allowed in wiring for H. T. arcs ; neither can the wires be run in moulding or conduit. It has been customary to use no smaller than No. 6 wire for these high tension series circuits. The current required is seldom more than 10 amperes, and No. 14 wire has sufficient carrying capacity, but its mechanical strength is not very great. The danger from a broken wire in high tension sys- tems is much greater than in low tension systems, because of the long arc which occurs at the break. The loss in volts per 100 feet with No. 6 will be about .4, while with No. 14 it will be 2.6. This, however, will not affect the lights, because the pressure at the machine must be correspondingly increased. d. Must be supported on glass or porcelain insulators, which separate the wire at least one inch from the surface wired over, and must be kept rigidly at least eight inches from each other, except within the structure of lamps, on hanger- boards or in cut-out boxes, or like places, where a less distance is necessary. An extra precaution often taken in this kind of work on plastered walls is ta place a wooden block or rosette about three inches in diameter and one-half inch thick under each insu- lator ; this secures greater separation from ceilings and side walls and adds greatly to the stability of the insulators. On plastered walls a small insulator, if subjected to side strain, will cut into the plaster on one side and allow the wires to sag, the wooden block will prevent this. e. Must, on side wall, be protected from mechrnical injury by a substantial boxing, retaining an air space of one inch around the conductors, closed at the top (the wires passing through bushed holes), and extending not less than seven feet from the floor. When crossing floor timbers in cellars, or in rooms where they might be exposed to injury, wires 112 MODERN ELECTRICAL CONSTRUCTION. must be attached by their insulating supports to the under side of a wooden strip not less than one-half an inch in thick- ness. Instead of the running-boards, guard strips on each side of and close to the wires will be accepted. These strips to be not less than seven-eighths of an inch in thickness and at least as high as the insulators. Except on joisted ceilings, a strip one-half of an inch thick is not considered sufficently stiff and strong. For spans of say eight or ten feet, where there is but little vibration, one-inch stock is generally sufficiently stiff; but where the span is longer than this or there is considerable vibration, still heavier stock should be used. For general suggestions as to protecting wires on side walls, see notes under No. 24 e. Figure 59 is an illustration of protection on side walls, giving the dimensions required. The wooden block shown, which raises bushings above floor, is an extra protection to .k Figure 59 prevent water from running into them. The iron pipe is shown extending in one piece clear through the floor. With voltages used in this system a separate pipe should be pro- vided for each wire, unless alternating currents are used. CONSTANT CURRENT SYSTEMS. llo 19. Series Arc Lamps. (For construction rules, see No. 57.) a. Must be carefully isolated from inflammable, material. b. Must be provided at all times with a glass globe sur- rounding the arc, and securely fastened upon a closed base. Broken or cracked globes must not be used. c. Must be provided with a wire netting (having a mesh not exceeding one and one-fourth inches) around the globe, and an approved spark arrester (see No. 58), when readily inflammable material is in the vicinity of the lamps, to prevent escape of sparks of carbon or melted copper. It is recom- mended that plain carbons, not copper-plated, be used for lamps in such places. Outside arc lamps must be suspended at least eight feet above sidewalks. Inside arc lamps must be placed out of reach or suitably protected. Arc lamps, when used in places where they are exposed to flyings of easily inflammable material, should have the car- bons enclosed completely in a tight globe in such manner as to avoid the necessity for spark arresters. "Enclosed arc" lamps, having tight inner globes, may be used, and the requfrements of Sections b and c above would of course, not apply to them, except that a wire netting around the inner globe may in some cases be required if the outer globe is omitted. d. Where hanger-boards (see No. 56) are not used, lamps must be hung from insulating supports other than their con- ductors. At the left, Figure 60 is shown, the usual method of sus- pending outdoor arc lamps on buildings. The supporting wire may be fastened to brick or stone walls by drilling a hole about four inches deep and plugging this securely with wood, when an eye or lag bolt or large spike may be driven or screwed into it. Expansion bolts, of which there are many kinds to be had, may also be used. It is best to arrange the supporting wires at quite a high angle, otherwise the direct outward pull may be too great. Some of the older arc lamps are not provided with insulators, and may be suspended, as shown in the center of the figure. On very low ceilings, lamps are often arranged 114 MODERN ELECTRICAL CONSTRUCTION. as shown at the right, the plastering being cut away and lamp suspended from floor above joists. The space above plaster Figure 60 must be enclosed on all sides and all v;oodwork protected with asbestos board at least one-eighth inch thick. If this method is used with constant potential arc lamps carrying resistance in the hood, it would be well to remove or short-circuit this resistance and locate another in a more suitable place. 20. Incandescent Lamps in Series Circuits. a. Must have the conductors installed as required in No. 18, and each lamp must be provided with an automatic cut-out. b. Must have each lamp suspended from a hanger-board by means of rigid tube. c. No electro-magnetic device for switches and no mul- tiple-series or series-multiple system of lighting will be approved. d. Must not under any circumstances be attached to gas fixtures. CONSTANT-POTENTIAL SYSTEMS. GENERAL RULES ALL VOLTAGES. 21. Automatic Cut-Outs (Fuses and Circuit-Breakers). (Sec No. 17, and for construction, Nos. 52 and 53.) Excepting on main switchboards, or where otherwise sub- CONSTANT POTENTIAL SYSTEMS. 115 ject to expert supervision, circuit-breakers will not be ac- cepted unless fuses are also provided. The cut-out is the. principal protective device used in elec- tric light and power work. In its simplest form it consists of a piece of wire made^ of a certain alloy designed to melt at a comparatively low temperature and so connected that all current used in a certain circuit must pass through it. We have already seen that currents of electricity generate heat in the conductors through which they pass, and that this heat is proportional to the square of the current flowing; that is, if we double the current we shall increase the production of heat fourfold. A dangerous rise in current strength may be due to a "short circuit' or to an overload, too many lamps or motors being connected to a circuit. To prevent damage to wires and other apparatus from excessive currents, fuses or cut-outs must be installed. When the current rises above its allowed strength the fuse melts and opens the circuit; that is, stops all current flow. This melting of the fuse is always accompanied by a flash of fire, called an arc, and may easily set fire to inflammable material located near the fuses. In the case of large fuses pieces of molten lead are often spattered about. Another device used for the same purpose as the fuse or cut-out is known as the circuit-breaker. A circuit-breaker in its simplest form comprises a knife switch which when closed is forced in against a spring and held in place by means of a small catch. A solenoid, inside of which is placed a moveable iron core, is connected in series with one side of the switch. When the current passing through this solenoid exceeds a certain amount, the iron core is drawn up into it, and, striking against the catch, releases the switch which will then fly open, thus cutting off the current. The core of this solenoid is so designed that when it starts to move its speed is greatly accelerated so that it strikes the catch a sharp 116 MODERN ELECTRICAL CONSTRUCTION. blow. By means of a small adjusting screw the circuit break- er can be set to operate at various current strengths within its limits. For this reason and for the further reason that it is so easily made inoperative by tying or blocking its sol- enoid it is not approved for general use unless fuses are also installed. It may be used under the care of a competent elec- trician who understands the dangers of its abuse. a. Must be placed on all service wires, either overhead or underground, as near as possible to the point where they enter the building and inside the walls, and arranged to cut off the entire current from the building. Where the switch required by No. 22 is inside the build- ing, the cut-out required by this section must be placed so as to protect it. In risks having private plants, the yard wires running from building to building are not generally considered as ser- vice wires, so that cut-outs would not be required where the wires enter buildings, provided that the next fuse back is small enough to properly protect the wires inside the building in question. The fuse block here required serves a double purpose; it affords protection to the whole installation while in use, and is an effective means of disconnecting a building when cur- rent is no longer used. This can also be accomplished by means of the service switch, but a switch is so easily closed by anyone that it must never be relied upon entirely for this purpose. Figure 61 shows arrangement of fuses and switch as commonly installed where wires enter buildings. The wires enter at the top, connect to the fuse terminals, cur- rent passing through the fuses to the switch. b. Must be placed at every point Fig. 61. CONSTANT POTENTIAL SYSTEMS. 117, where a change is male in the size of wire [unless the cut- out in the larger wire will protect the smaller (see No. 61)]. Figure 62, A to D, shews systems of distribution and ar- rangement of mains in ger.eral use. Figure A shows the simplest and cheapest method ^f running mains, and is known as the "tree system." Beginning at the service the wires must be large enough to carry the whole current to the first floor or wherever the first cut-out center is located. At this point the size of wire may be reduced because it will be required to carry only the current used further on. Main cut-outs should be arranged as shown in the figure at 1 and 2. That is, the cut-outs protecting the mains must be in- stalled in the mains at each floor after the current for that floor has been taken off. Cases are often found where the cut-out is placed in the main line ahead of the branch blocks. This is obviot'.sly wrong, as the fuse will have to be too heavy to protect the smaller mains. Figure B shows a somewhat different arrangement which requires more wire and is more expensive in the beginning, but far more satisfactory and economical in operation. With the wires arranged as shown in the diagram the pressure at all the lamps will be nearly uniform. Even if the mains are designed for a considerable loss to the center of dis- tribution the dynamo may be made to compensate for this loss and keep the lamps burning properly. With the tree system, A, this is impossible ; the lamps at the first cut-out center will either be too bright or those at the last center too dim. Figure C shows a convertible three-wire system. Three- wire circuits may also be run as shown in Figures A and B, using three instead of two wires. In order to convert a three-wire system into a two-wire system the two outside wires are joined together. The mid- dle wire then forms or.e side of the system and the outside 118 MODERN ELECTRICAL CONSTRUCTION. Figure 62 CONSTANT POTENTIAL SYSTEMS. 119 wires the other. The middle wire must carry as much cur- rent as both outside wires combined and should have a carry- ing capacity equal to them. It should be remembered that a wire containing simply twice as many circular mils does not fulfil this requirement as is shown in the table on page which must be consulted in selecting wires. In three-wire systems the middle or neutral wire is merely a balancing wire and normally carries very little or no current, but it is very important that it remain intact. If for instance in Figure D the branch circuit a has twelve lights burning while there are also 12 lights burning on b, the current will pass from the positive wire through the lower fuse to a, through the twelve lights in a back to the middle fuse, thence through the 12 lights in b to the upper fuse and negative wire, the two sets of lamps burning in series. If now the lamps in b are switched off the current from a can no longer pass through them and instead returns through the middle fuse to the neutral wire. If only six lights in b are burning, while 12 are burning in a, the current of 6 lights will return over the negative wire and the other six in a will return over the neutral wire. Should the neutral wire be broken or its fuse blown there would be no return path on it for the extra cur- rent, and consequently the current passing through the twelve lights in a would be forced through the six lights in b. caus- ing them to burn with excessive brilliancy and to break in a very short time. Should a short circuit occur, say on circuit b, with the neutral wire intact, it would merely blow a fuse, but if the main neutral fuse were out it would bring 220 volts on circuit a and speedily cause damage to the lamps. Thus it will be seen that it is of great importance to fuse the neu- tral wire so that it will not easily blow out. The cut-out shown in Figure D is not approved because it does not pro- vide independent double fused branch circuits. The style of wiring shown in connection with it was formerly much in vcr"c bvt is net now much used. 120 MODERN ELECTRICAL CONSTRUCTION. Figure C shows a system of wiring quite often used. A set of heavy mains are run from the service or dynamo to the top floor and taps taken off at each floor. These mains do not change size at each fleer, but are continuous for their en- tire length. While this method has some of the objections of the tree system in regards to voltage, still the faults of the tree system are greatly reduced to the much smaller losses in the mains between the upper floors or those farthest from the dynamo. Figure 63 shows the method of fusing main switch and branch circuits. The switch itself will require a fuse to pro- tect it although it need not be right at the switch. It often becomes necessary to reinforce a set of mains, especially for motors which have become overloaded, by run- ning another wire in parallel with the old as indicated in Figures 64 and 65. Two separate and distinct ways of ar- Fig. 63 Fig. 64 Fig. 65 Fig. 66 ranging them are shown and it depends upon the conditions as to which is preferable. If the wires are small or run in places where they are liable to be broken, the plan shown in Figure 64 is the better. Here each wire is properly fused and if one breaks the other carries the whole load until its fuse CONSTANT POTENTIAL SYSTEMS. 121 melts. If the wires, as often happens, are much overfused, the breaking of one wire would force the other to carry the whole current and become overheated. If the arrange- ment were as in Figure 65 the unbroken wire would carry the current indefinitely and soon become overheated. On the other hand, if both wires are large and the run is short the fuses arranged as in Figure 64 may, through poor contacts, prevent one or the other of the wires from obtaining its full share of the current. The fuse making poor contact would force a much greater share of current through the other wire. In most cases the better plan would be to ar- range the wires as in Figure 65. If the current supplied is for lights the branch cut-outs can be separated and each set of mains allowed to supply a certain part of them, when each set should be made independent. For sizes of wires to be used for reinforcing, see Tables. With the three-wire system where a larger motor load and a few lights are run the lights are often fused as shown in Figure 66, a small wire being run for the neutral, this smaller wire, of course, being properly fused at the main cut- out. Plug cut-outs of the type shown in this figure often have the metal parts projecting above the porcelain ; they should be connected so that the metal parts which project are dead when the plugs are removed. This will prevent many short circuits on disconnected cut-outs. Figure 67 shows the method of converting a two-wire system into a three-wire system with one extra wire to run. This extra wire will very likely not need to be as large as the other wires are, because the three-wire system requires only one-half as much current and it should, therefore, be used as the neutral. This arrangement will secure the full benefit of all the copper in the old wires (which are probably much larger than necessary) and will operate at a very small loss. Figure 68 shows a straight three-wire system changed to 122 MODERN ELECTRICAL CONSTRUCTION. a two-wire system, one extra wire run for it. If the three wires are of the proper capacity the addition of the fourth wire as in the figure will make it correct for two-wire sys- Figure 67 Figure Figure 69 terns, the mains feeding the upper and lower groups being, of course, properly fused where they start. In Figure 69 the cut-outs are so connected that all branch wires leaving the cut-out box at either side are of the same polarity. This is often useful where many wires are to be run close together. c. Must be in plain sight, or enclosed in an approved cabinet (see No. 54), and readily accessible. They must not be placed in the canopies or shells of fixtures. The ordinary porcelain link fuse cut-out will not be ap- proved. Link fuses may be used only when mounted on slate or marble bases conforming to No. 52 and must be enclosed in dust-tight, flreproofed cabinets, except on switchboards located well away from combustible material, as in the ordi- nary engine and dynamo room and where these conditions will be maintained. CONSTANT POTENTIAL SYSTEMS. 123 While it is required that cut-out cabinets be accessible there is also danger in making them too accessible, for such cabi- nets are very often used for storage of paper or cotton waste. It would seem that about eight feet above the floor is the most desirable height to place them or the cabinet may be arranged with a slanting bottom which will make it impossible to store anything in it. It is also well to arrange the cut-out cabinet away from inflammable material, for long experience has shown that doors are nearly always left open. Especially is this the case when switches are in the same cabinets with the cut-outs. d. Must be so placed that no set of incandescent lamps requiring more than 660 watts, whether grouped on one fixture or on several fixtures or pendants, will be dependent upon one cut-out. Special permission may be given in writing by the Inspection Department having jurisdiction for departure from this rule in the case of large chandeliers, stage borders and illuminated signs. The above rule shall also apply to motors ,when more than one is dependent on a single cut-out. The idea is to have a small fuse to protect the lamp socket and the small wire used for fixtures, pendants, etc. It also lessens the chances of extinguishing a large number of lights if a short circuit occurs. "On open work in large mills approved link fused ro- settes may be used at a voltage of not over 125 and approved enclosed fused rosettes at a voltage of not over 250, the fuse in the rosettes not to exceed 3 amperes, and a fuse of over 25 amperes must not be used in the branch circuit." All branches or "taps" from a three-wire Edison system must be run as two-wire circuits. c. The rated capacity of fuses must not exceed the allow- able carrying capacity of the wire as given in No. 16. Circuit- breakers must not be set more than 30 per cent above the al- lowable carrying capacity of the wire, unless a fusible cut-out is also installed in the circuit. A 16 c. p. incandescent lamp is usually estimated at 55 watts and consequently the number of lamps allowed on one circuit is usually twelve, whether 110 or 220 volts are used. 124 MODERN ELECTRICAL CONSTRUCTION. If voltages lower than 110 are us. I the current required by twelve 55 watts lamps will be too great, and fewer lamps should be used per circuit. Although a number of small fan motors may be run on one circuit each motor should be pro- vided with a switch ; as a rule such a switch is on the motor. 22. Switches. (Sec No. 17, and for construction, No 51). a. Must be placed on all service wires, either overhead or underground, in a readily accessible place, as near as possible to the point where the wires enter the building and arranged to cut off the entire current. Service cut-out and switch must be arranged to cut off current from all devices Including meters. In risks having private plants the yard wires running building are not generally considered as ser- vice wires, so that switches would not be required in each from building to building are not , building if there are other switches conveniently located on the mains or if the generators are near at hand. In overhead construction the best plan is to locate the switch at either front or rear of building so that wires may lead to it direct from pole. Avoid running wires on sides of building where it is likely that other buildings may be erected. In underground construction, where the space under sidewalk and basement is not occupied, it is advisable to place a cut-out where wires enter the building from street and to locate the service switch in a more accessible place. Although the rules do not call for switch to be installed in each separate building in the case of large plants, still it is often advisable to install them, for in case of trouble it is nec- essary that the current can be immediately shut off. A switch is also useful in cases of trouble on the wiring, to allow of repairing. b. Must always be placed in dry, accessible places, and be grouped as far as possible. Knife switches must be so placed that gravity will tend to open rather than close them. CONSTANT POTENTIAL SYSTEMS. 125 "When possible, switches should be so wired that l/.ades will be "dead" when switch is open. If knife switches are used in rooms where combustible flyings would, be likely to accumulate around them, they should be enclosed in dust-tight cabinets. (See note under No. 17 b.) Even in rooms where there are no combustiblo materials it is better to put all knife switches in cabinets, in order to lessen the danger of accidental short circuits being made across their exposed metal parts by careless workmen. Up to 250 volts and thirty amperes, approved indicating snap switches are advised in preference to knife switches on lighting circuits abcut the workrooms. To comply with this rule will ordinarily bring the fuses of knife switches directly under the handle of switch. If there happens to be a short circuit 0:1 the \vires when switch is closed the fuses will blow instantly and very li'.iely burn the operator's hand. In connection with such switches cartridge fuses should be used or the switches, especially the larger ones, closed by O II Figure 70 Figure 71 pushing them in with a stick. The danger from opening a switch is much less. Figure 70 shows a switch arranged to comply with all three points of this rule, the feed wires coming from bebw. This requires that incoming and outgoing wires pass e-ach other. In this case, the wires pass each other behind the switch base, 126 MODERN ELECTRICAL CONSTRUCTION. they being encased in flexible tubing. A side view is also given in Figure 71. Instead of passing behind the switch the wires may, of course, run around one side to the top, the other wires around the other side to the bottom. Figure 71 illustrates a cabinet so arranged that the switch within can be opened or closed without opening the cabinet. The cover Is hinged at the top, and slotted in the center, which leaves room for the lever by which the switch is worked to adjust itself so it will always be out of the way. A switch which is often used may as well be left without a cover as with one, for the door must be opened or closed every time the switch is used, and the cabinet will always be found open. Figure 71 will answer where only protection against acci- dental contacts is required. c. Must not be single pole when the circuits which they control supply devices which require over 660 watts of energy, or when the difference of potential is over 300 volts. This rule allows the use of single pole switches on circuits of 660 watts, 6 amperes at 110 vots, or 3 amperes at 220 volts, which corresponds roughly to twelve 16 cp. lamps. In systems that are not grounded a single pole switch will answer fairly Figure 72 well if large enough. It will readily open the circuit and it offers no opportunities for short circuits, as do double pole switches. Where, however, three wire systems with grounded neutrals are used double-pole switches are preferable, for by reference to Figure 72 one can readily see that if the neutral CONSTANT POTENTIAL SYSTEMS. 127 or middle wire is grounded (which is equivalent to being in connection with gas piping) and another ground should come on to the wiring say at a, the single-pole switch, S, would not control the lights at all. The current would flow from the positive wire to the top fuse, through the twelve lights to ground a, through the ground to the neutral or middle wire and back to the dynamo, regardless of whether the switch is on or off. Also, a man working at the lights could easily make a short-circuit by bringing the wires into contact with the gas piping even if the switch were turned off. When single-pole switches are used in connection with such circuits they should never be placed in the neutral wire as in the dia- gram. If the switch S were placed in the top wire these troubles would be avoided. Often times, however, switches are connected before the circuits are run into cut-outs and an attempt to place single-pole switches on a certain wire requires considerable care, which many wiremen will not take. In the case of only two wires from a central, three-wire, station being run into a building, the neutral wire is not known until meters are set and instructions would, therefore, have to be left for meter men which would often be disregarded, so that in all cases on three-wire grounded systems double-pole switches are preferable. d. Where flush switches are used, whether with conduit systems or not, the switches must be enclosed in boxes con- structed of iron or steel. No push buttons for bells, gas- lighting circuits, or the like shall be placed in the same wall plate with switches controlling electric light or power wiring. This requires an approved box in addition to the porce- lain enclosure of the switch. e. Where possible, at all switch or fixture outlets, a %-mch block must be fastened between studs or floor timbers flush with the back of lathing to hold tubes, and to support switches or fixtures. When this cannot be done, wooden base blocks, not less than 24-inch in thickness, securely screwed to lathing, 128 MODERN ELECTRICAL CONSTRUCTION. must be provided for switches, and also for fixtures which are not attached to gas pipes or conduit tubing. Figure 73 shows concealed wiring back of lathing leading to a double-pole flush switch. The board fastened between studdings must be cut out to admit the box of switch and the II Figure 73 Figure 74 size of this box should be known when wires are put in. The board should not rest hard against the lathing, but leave a little space for plaster to work in behind the lath. Loom is put on all wires at outlets and must extend back to the nearest knob. Figure 74 shows two methods of fastening snap switches by means of wooden blocks first fastened to the plaster. One block is cut out so as to bring all wires under the switch and entirely conceal them. The opening in block to admit wires and bushings should be oblong, so as to leave room on two sides for the screws with which the switch is to be fastened. On the other block the wires and bushing are brought through close to the outer edge of switch base. By careful workman- ship a neat job can be done in this way. As most snap switches cross conductors, that is, connect points a and b, if CONSTANT POTENTIAL SYSTEMS. 129 from the nature of the case it becomes necessary to run any of the wires close together these two wires may.be run that way, for they can never be of opposite polarity. 23. Electric Heaters. a. Must be placed in a safe situation, isolated from inflam- mable materials, and be treated as sources of heat. b. Must each have a cut-out and an indicating switch (see No. 17 a). ,r. The attachments of feed wires to the heaters must be in plain sight, easily accessible, and protected from interference, accidental or otherwise. d. The flexible conductors for portable apparatus, such as irons, etc., must have an approved insulating covering (see No. 45 g). e. Must each be provided with name-plate, giving the maker's name and the normal capacity in volts and amperes. Figure 75 Stationary heaters should be treated like stoves which might become overheated at any time. Portable heaters, such as flat irons, have this danger, that if left standing with the current on they in time accumulate heat enough to char combustible material and to finally set it on flre. It is often desirable to connect in multiple with the heat- ers, an incandescent lamp of low candle power, as it shows at a glance whether or not the switch is open, and tends to prevent its being left closed through oversight. 130 MODERN ELECTRICAL CONSTRUCTION. In Figure 75 is given a diagram of a heater circuit with a 4 cp. lamp in circuit. Where there are many irons in use, as in some tailoring establishments, it is advisable to run them all from one set of mains with a main switch convenient to exit door and have this switch opened whenever the irons are not in use. The individual switch at each iron should be located as near as possible to each iron. Cords feeding irons or cloth cutting machines are often installed as shown, insulators are strung on a tight wire and the cord tied to them. This allows considerable latitude in moving the iron. LOW POTENTIAL SYSTEMS. 131 Low-Potential Systems. 550 VOLTS OR LESS. Any circuit attached to any machine, or combination of ma- chines, which develops a difference of potential between any two wires, of over ten volts and less than 550 volts, shall be considered as a low-potential circuit, and as com- ing under this class, unless an approved transforming de- vice is used, which cuts the difference of potential doivn to ten volts or less. The primary circuit not to exceed a potential of 3,500 volts. Before Pressure is raised above 300 volts on any previously existing 1 system of wiring-, the whole must be strictly brought up to all of the requirements of the rules at date. 24. Wires. GENERAL RULES. (Sec also Nos. 14, 15 and 16.) a. Must be so arrang-ed that under no circumstances will there be a difference of potential of over 300 volts between any bare metal parts in any distributing- switch or cut-out cabinet, or equivalent center of distribution. This rule, as far as it applies to pressures higher than 300 volts, contemplates a 3-wire system on which, instead of the -2tO - 1-220 ' Figure 76 customary 110 volts on each side of the neutral, 220 volts are used, making a pressure of 440 volts between the two outside wires. 132 MODERN ELECTRICAL CONSTRUCTION. The ordinary 110-220 volt, 3-wire system will require to be changed at cut-out centers as shown in Figure 76, where it will be seen a difference of potential greater than 220 volts can- not be found within any cut-out box, or at any switch or cut- out. Special attention should be given to the balancing of the load with this arrangement of wiring and both sides of the system should be brought into every room or hall requiring Figure 77 more than one circuit. False ideas of economy should not induce one to arrange large groups of lamps on one side of the system in order to save a few cut-out boxes. 6. Must not be laid in plaster, cement, or similar finish, and must never be fastened with staples. LOW POTENTIAL SYSTEMS. 133 c. Must not be fished for any great distance, and only in places where the inspector can satisfy himself that the rules have been complied with. Figure 77 illustrates a very common combination of "fish" and "moulding" work. Moulding is used to bring the wires from the floor to the ceiling and along the ceiling to a point opposite the outlet and parallel with the joists. From this point to the fixture the wires can then be readily fished. The connection between the fish and moulding work should be made as shown at the right, where ihe moulding is cut out so as to admit the loom. It is better, even, to have the loom show to some extent than to have the wire come in contact with the plaster, as will very likely be the case if the loom is not fully brought through. d. Twin wires must never be used, except in conduits, or where flexible conductors are necessary. Flexible conductors are in general considered necessary only with pendant sockets, certain styles of adjustable brack- ets, portable lamps, motors and stage plugs, or heating ap- paratus. e. Must be protected on side walls from mechanical injury- When crossing floor timbers in cellars, or in rooms where they might be exposed to injury, wires must be attached by their insulating supports to the under side of a wooden strip, not less than one-half inch in thickness, and not less than three inches in width. Instead of the running boards, guard strips on each side of and close to the wires will be accepted. These strips to be not less than seven-eighths of an inch in thickness, and at least as high as the insulators. Suitable protection on side walls may be secured by a sub- stantial boxing, retaining an air space of one inch around the conductors, closed at the top (the wires passing through bushed holes), and extending not less than five feet from the floor; or by an iron-armored or metal-sheathed insulating conduit suf- ficiently strong to withstand the strain to which it will be sub- jected, and with the ends protected by the lining or by special insulating bushings, so as to prevent the possibility of cutting 134 MODERN ELECTRICAL CONSTRUCTION. the wire insulation; or by plain metal pipe, lined with approved flexible tubing, which must extend from the nsulator next below the pipe to the one next above it. If metal conduits or iron pipes are used to protect wires car- rying alternating currents, the two or more wires of each cir- cuit must be placed in the same conduit, as troublesome induc- tion effects and heating of the pipe might otherwise result; and the insulation of each wire must be reinforced by approved flex- ible tubing extending from the insulator next below the pipe to the one next above it This should also be done in direct-cur- rent wiring if there is any possibility of alternating current ever being used on the system. For high-voltage work, or in damp places, the wooden boxing may be preferable, because of the precautions which would be necessary to secure proper insulation if the pipe were used. With these exceptions, however, iron pipe is considered prefer- able to the wooden boxing, and its use is strongly urged. It is especially suitable for the protection of wires near belts, pul- leys, etc. f. When run in unfinished attics, or in proximity to water tanks or pipes, will be considered as exposed to moisture. Figure 78 Figure 78 illustrates the meaning of the rule in regard to wires run along low ceilings. Figure 79 gives the dimensions necessary for boxing wires on side walls. At the right, the sidewall protection consists of conduit; a junction box with the lower side knocked out is used to enclose bushings. When the cover is screwed on the wires are completely enclosed. LOW POTENTIAL SYSTEMS. 135 SPECIAL RULES. For Open Work. In dry places. g. Must have an approved rubber or "slow-burning weath- erproof" insulation (see Nos. 41 and 42.) A "slow-burning weatherproof" covering is considered good enough where the wires are entirely on insulating supports. Its main object is to prevent the copper conductors from com- ing accidentally into contact with each other or anything else. Most of this wire as it is now made with the weather-proof braid on the outside, becomes sticky when exposed to the tern- Figure 79 perature found in most mill rooms in summer. This is objec- tionable, especially in linty places, as dust and flyings readily adhere to the wires, making it difficult to keep them clear. Under these conditions, the "sweeping-down" process generally results in loosening and deranging the wires in a short time. The weatherproof insulation is also very combustible, and 136 MODERN ELECTRICAL CONSTRUCTION. when on the outside might allow fire to spread along the wires, especially if there were a number of wires near together, as stated in the note to No 2 b For these reasons it is considered preferable to place the weatherproof insulation next to the con- ductor, and the slow-burning braids on the outside. The outer surface should then be finished hard and smooth, similar to that on the old so-called "underwriter" wire A wire insulated in this manner is not open to the objections noted above, and can also be more readily drawn into flexible tubing where the iron pipe construction described in the note to Section e is used. h. Must be rigidly supported on non-combustible, non- absorptive insulators, which will separate the wires from each other and from the surface wired over in accordance with the following table : Voltage. Distance from Distance between Surface. Wires. to 300 301 to 550 %inch 1 Inch 2% inch 4 inch Rigid supporting requires under ordirfary conditions, where wiring along flat surfaces, supports at least every four and one-half feet. If the wires are liable to be disturbed, the dis- tance between supports should be shortened. In buildings of mill construction, mains of No. 8 B. & S. gage wire or over, where not liable to be disturbed, may be separated about six inches, and run from timber to timber, not breaking around, and may be supported at each timber only. This rule will not be interpreted to forbid the placing of the neutral of an Edison three-wire system in the center of a three- wire cleat where the difference of potential between the outside wires is not over 300 volts, provided the outside wires are sep- arated two and one-half inches. Figure 80 shows different methods of running wires in buildings of mill construction. If the method shown at a is Figure 80 used, a few insulators should be placed here and there and the wires tied to them to prevent sagging. The arrangements shown at b and c are suitable for small wires on high ceilings. LOW POTENTIAL SYSTEMS. 137 The methods shown at d and c are sometimes used where there is no danger of interference. With long spans, supports as shown at f may be used. In damp places, or buildings specially subject to moisture or to acid or other fumes liable to injure the wires or their insulation. i. Must have an approved insulating covering. For protection against water, rubber insulation must be used. For protection against corrosive vapors, either weath- erproof or rubber insulation must be used (See Nos 41 and 44.) j. Must be rigidly supported on non-combustible, non-ab- sorptive insulators, which separate the wire at least one inch from the surface wired over, and must be kept apart at least two and one-half inches for voltages up to 300, and four inches for higher voltages. Rigid supporting requires under ordinary conditions, where wiring over flat surfaces, supports at least every four and one- half feet. If the wires are liable to be disturbed, the distance between supports should be shortened. In buildings of mill construction, mains of No. 8 B. & S. gage wire or over, where not liable to be disturbed, may be separated about six inches, and run from timber to timber, not breaking around, and may be supported at each timber only. k. (Stricken out.) In damp places the wires are often run on the under side of an inverted trough as shown in Figure 81. The main point of usefulness of such a trough lies in the fact that it prevents drippings from wetting the wires and insulators. Condensa- tion will, however, keep insulators and wires wet nevertheless. The trough, to be useful, should be put together with many screws, the butting edges of the boards having been first painted with a waterproof paint, with which, when finished, the whole trough is also painted inside and out. Notwithstanding the rule given above, it would seem far better where practicable to use petticoat insulators and keep them much farther apart, even, if in order to do so a larger wire would be required. Each insulator, when wet, allows some current to leak over its surface and, therefore, the 138 MODERN ELECTRICAL CONSTRUCTION. fewer we have the better so long as there is no danger of break- ing wires. If splices are necessary in wet places they should be made quite a distance from insulators; the insulation of a splice being always weaker than that of the unbroken wire. Care should also be taken that the insulation of wires is not damaged through tying. Weather proof sockets are required by the rule and are Figure 81 best in such places when not subject to much handling. As these are, however, easily broken, brass shell sockets are often used. These are thoroughly covered with tape and compound so as to exclude all moisture and are very durable. For Moulding Work. /. Must have an approved rubber insulating covering (see No. 41). m. Must never be placed in moulding in concealed or damp places, or where the difference of potential between any two wires in the same moulding is over 300 volts. As a rule, moulding should not be placed directly against a brick wall, as the wall is likely to "sweat" and thus introduce moisture back of the moulding. Figure 82 shows the dimensions of approved moulding. Figure 83 shows the proper method of making a tap joint LOW POTENTIAL SYSTEMS. 139 in moulding. This method brings the capping between the two wires of opposite polarity. Wires should never be crossed be- low the capping. If the exposed wire in Figure 83 is objec- tionable, part of the back of moulding may be cut out, or the Figure 82 Figure 83 wall back of the moulding may be gouged out as shown in Fig- ure S4. This method must, however, never be used with other than walls or partitions of hardwood. Figure 85 shows proper method of tapping flexible cord to Fig. 84 Figure 85 wires in moulding. The whole cord should never be taken out of one hole in capping. There is always some chance of abrasion and joints are often poorly covered, so that there is always mere likelihood cf ?hort circuits at this point. 140 MODERN ELECTRICAL CONSTRUCTION. Figure 86 shows how moulding should be fastened to tile ceiling. When toggle bolts are used, the nut should always be put on outside of capping (unless a very small one is used, or Figure 87 Figure 88 more than ordinary care is exercised). Many wiremen are careless and cut away the middle tongue too much, giving the nut a chance to work itself diagonally across it, so as to come in contact with both wires and, in time perhaps, cause short circuits. Although toggle bolts are mostly used, screws have been successfully used in tile. It is only necessary to first drill a hole of just the proper size for the screw to be used. A very rough, quick way of making a square turn with moulding is shown in Figure 87. One piece is cut entirely off along the line a; the pieces are then joined as shown and Figure the capping hides the botch work. Such work will not be passed by inspectors if noticed. The proper way of fitting moulding is shown in Figure 88. LOW POTENTIAL SYSTEMS. 141 Figure 89 shows methods of running round corners. The saw cuts, a, b, c, etc., should be made with a fine saw and for short bends require to be close together. Bending is facilitated by wetting the moulding ar.d if, before the moulding is put in place, the saw cuts are filled with glue, it will greatly add to the durability of the job. Screws or nails used in fastening the capping should pass through the moulding into the wall to get a firm hold. For Conduit Work. n. Must have an approved rubber insulating covering (see No. 47). o. Must not be drawn in until all mechanical work on the building has been, as far as possible, completed. p. Must, for alternating systems, have the two or more wires of a circuit drawn in the same conduit. It is advised that this be done for direct-current systems also, so that they may be changed to alternating systems at any time, induction troubles preventing such a change if the wires are in separate conduits. "The same conduit must never contain circuits of different systems, but may contain two or more circuits of the same system." If a single wire carrying alternating currents of electricity were run in iron pipe, there would be a very large drop in voltage. This drop is due to the fact that all currents while changing in strength generate a counter E. M. F. in their sur- roundings. This is particularly strong when the wires are sur- rounded by, or very close to, iron. If both wires are run in the same pipe, the current in one wire neutralizes that of the other and there is no trouble. For Concealed "Knob and Tube" Work. q. Must have an approved rubber insulating covering (see No. 41). r. Must be rigidly supported on non-combustible, non-ab- 142 MODERN ELECTRICAL CONSTRUCTION. sorptive insulators which separate the wire at least one inch from the surface wired over. Must be kept at least ten inches apart, and, when possible, should be run singly on separate timbers or studdings. Must be separated from contact with the walls, floor timbers and partitions through which they may pass by non-combustible, non-absorptive insulating tubes, such as glass or porcelain. Rigid supporting: requires under ordinary conditions, where wiring along flat surfaces, supports at least every four and one- half feet. If the wires are liable to be disturbed, the distance between supports should be shortened. s. "When, in a concealed knob and tube system, it is im- practicable to place any circuit on non-combustible supports of glass or porcelain, approved metal conduit, or approved armored cable must be used (see No. 24 f) except that if the difference of potential between the wires is not over 300 volts, and if the wires are not exposed to moisture, they may be LOW POTENTIAL SYSTEMS. 143 fished on the loop system, if separately encased throughout in continuous lengths of approved flexible tubing." An illustration of wiring on the "loop" system is shown in Figure 90. This system makes it unnecessary to have any concealed joints or splices. The amount of wire required is somewhat in excess of that required for tap systems, but this is often balanced by a saving in labor. Sometimes, however, the labor is also in excess of that required for tap systems. The main advantage of the system is that all joints and splices are always accessible. The figure also shows mixed "knob and tube" work and "conduit" work. Along the walls behind the furring strips there is seldom sufficient space to admit of knob and tube work and conduit must be used. /. "Mixed concealed knob and tube work as provided for in No. 24 s, must comply with requirements of No. 24 n to p, and No. 25, when conduit is used, and with requirements of No. 24 A, when armored cable is used." . Must at all outlets, except where conduit is used, be protected by approved flexible insulating tubing, extending in continuous lengths from the last porcelain support to at least one inch beyond the outlet. In the case of combination fix- tures the tubes must extend at least flush with outer end of gas cap. Figure 91 is drawn to illustrate "fish work." Fish work is used in finished buildings, mostly, and is often very tedious and expensive. Hours are sometimes spent before wires can be brought through and often the effort is an entire failure. In combination work, as shown in Figure 77, there is usually little trouble, as there is the whole span between joists to run wires in. An effort to fish at right angles to the joists (when there are strips under joists) is more difficult, but often suc- cessful if the distance is not too great. When there are two men the usual method of fishing is : One man takes a wire sufficiently long to reach from one open- ing to the other, and, after bending a small hook on one end 144 MODERN ELECTRICAL CONSTRUCTION. in such a way that it will not catch easily on obstructions, pushes this end into one opening and, by twisting and working backward and forward, gradually forces it toward the other opening. At this opening his helper is stationed with a short wire, also provided with a hook, with which he must seek to catch the other wire when it comes near his opening. When the two wires come in contact, the larger one is drawn out and the conducting wires (encased in approved flexible tubing) are fastened to it and drawn through. The tubing should always be put on the wires before drawing in. If it is put on Figure 91 later there is much temptation to leave it as indicated at the right of the figure at a. This trick is quite common, but is very easily detected by inspectors ; the wire at either end can easily be pushed in without pushing out at the other, as it would if the tubing were continuous. If the tubing has been taped to the wires this will be impossible, but either one of the tubings can still be moved without moving the other, which would be impossible in a job properly done. The tubing must consist of one piece, and there must be only one wire in each tubing. LOW POTENTIAL SYSTEMS. 145 If one man is alone on a fish job, a handful of small wire is pushed into one opening in a manner which will allow it to spread out considerably. When the fish wire froni the other opening comes in contact with it, it will indicate it by moving this wire, which can be seen by that left hanging out. A small fish wire is then used to draw out the long one. If the two openings are in different rooms and not visible, one from the other, a bell and battery can be used, as shown in the drawing, if there are no wire lath. When wires are to be entirely concealed it is nearly always necessary to find a way through headers, timbers, etc. ; this can hardly be done without cutting holes in plaster. A method doing as little damage as any is shown at the top in Figure 91. A hole is bored through the 2X4, which will allow the wire, when job is finished, to continue downward as shown by dotted lines, 1 and 2. Such turns are seldom ever used with electric light wires on account of their size; they are more practicable with bell or telephone wires. Where it is desired to keep wires from showing in a parlor, for instance, they can be fished from an adjoining room, as indicated by dotted line 3, where the wires are run down partition in moulding in closet and then through to switch, which is in. the same room with the lights. Before under- taking a job of fish work it is well to look 'the whole building over carefully. There are often false walls along chimneys, especially at both sides of mantels, in which wires can be easily run from basement to attic. Often it may be necessary to remove baseboards in order to find room for wires. When removing such boards never attempt to drive nails out, always break them off; if driven out they will usually split off parts of the board. Soft wood floors can easily be taken up when necessary. Use a broad thin chisel and cut away the tongue on each side 14 , MODERN ELECTRICAL CONSTRUCTION. of the board to be taken up; the board can then be readily taken up. With double floors or with tightly laid hardwood floors, it is better to cut pockets in ceiling below. For Fixture Work. r. Must have an approved rubber insulating covering (see No. 46), and be not less in size than No. 18 B. & S. gage. w. Supply conductors, and especially the splices to fixture wires, must be kept clear of the grounded part of gas pipes, and, where shells or outlet boxes are used, thqy must be made sufficiently large to allow the fulfillment of this requirement. x. Must, when fixtures are wired outside, be so secured as not to be cut or abraided by the pressure of the fastenings or motion of the fixture. y. Under no circumstances must there be a difference of potential of more than 300 volts between wires contained in or attached to the same fixture. Rule 24 A. New Rule. Armored Cables. (For Construction Rules sec No. 48.) a. Must be continuous from outlet to outlet or to junction boxes, and the armor of the cable must properly enter and be secured to all fittings. NOTE In case of underground service connections and main runs, this involves running such armored cable continuously into a main cut-out cabinet or gutter surrounding the panel board, as the case may be. (See No. 54.) b. Must be equipped at every outlet with an approved out- let box or plate, as required in conduit work. (See No. 49 / to o.) Note. Outlet plates must not be used where it is practicable to install outlet boxes. In buildings already constructed where the conditions are such that neither outlet box nor plate can be installed, these appliances may be omitted by special permission of the Inspec- tion Department having jurisdiction, provided the armored cable is firmly and rigidly secured in place. c. Must have the metal armor of the cable permanently and effectively grounded. LOW POTENTIAL SYSTEMS. 147 NOTE It Is essential that the metal armor of such systems be joined so as to afford electrical conductivity sufficient to allow the largest fuse or circuit breaker in the circuit to operate before a dangerous rise in temperature in the system can occur. Armor of cables and gas pipes must be securely fastened in metal outlet boxes so as to secure good electrical connection. Where boxes used for centers of distribution do not afford good electrical connection, the armor of the cables must be joined around them by suitable bond wires. Where sections of ar- mored cable are installed without being fastened to the metal structure of buildings or grounded metal piping, they must be bonded together and joined to a permanent and efficient ground connection. d. When installed in so-called fireproof buildings in course of construction or afterwards if concealed, or where it is ex- posed to the weather, or in damp places such as breweries, stables, etc., the cable must have a lead covering at least 1/32 of an inch in thickness placed between the outer braid of the conductors and the steel armor. e. Where entering junction boxes at all other outlets, etc., must be provided with approved terminal fittings which will protect the insulation of the conductors from abrasion, unless such junction or outlet boxes are specially designed and ap- proved for use with the cable. f. Junction boxes must always be installed in such a man- ner as to be accessible. g. For alternating current systems must have the two or more conductors of the cable enclosed in one metal armur. 25. Interior Conduits. (Sec also Nos. 24 n to p, and 49.) The object of a tube or conduit is to facilitate the insertion or extraction of the conductors and to protect them from me- chanical injury. Tubes or conduits are to be considered merely as raceways, and are not to be relied upon for insulation be- tween wire and wire, or between the wire and the ground. The installation of wires in conduit not only affords the wires protection from mechanical injury, but also reduces the liability of a short circuit or ground on the wires producing an arc, which would set fire to the surrounding material; the conduit being generally of sufficient thickness to blow a fuse before the arc can burn through the metal of the pipe. For 148 MODERN ELECTRICAL CONSTRUCTION. this reason the wires should be entirely encased in metal throughout, both in the conduit and at all outlets. Another advantage derived from the use of iron conduit is the facility with which wires can be extracted and replaced in case a fault develops on any of them. The saving which this may mean in cases where the installation of new wires would necessitate the destruction of costly decorations can readily be seen. It must be remembered that the arc or burn produced by a short circuit or ground is proportional to the size of the fuse protecting the circuit. If a large fuse, say 30 amperes, is used to protect a branch circuit and a ground or short occurs on this circuit, the wire may become fused to the pipe so that it cannot easily be pulled out. This is one reason why fuses should be as small as practicable. More than six amperes is seldom used on branch circuits, so that no larger fuse than this should ordinarily be used. The installation of wires in iron conduit also reduces the liability of lightning discharges entering a building as the pipe surrounding the wires offers great resistance to the passage of these sudden currents. Conduit is classed under two general heads, lined and tin- lined. In both classes of conduit the same thickness of metal is required. a. No conduit tube having an internal diameter of less than five eighths of an inch shall be used. Measurements to be taken inside of metal conduits. This rule favors lined conduit insomuch that it requires the same pipe for lined and unlined, and allows a lined con- duit of less than five-eighths of an inch in diameter. 6. Must be continuous from outlet to outlet or to junc- tion boxes, and the conduit must properly enter, and be secured to all fittings. In case of underground service connections and main runs, this involves running each conduit continuously into a main cut-out cabinet or gutter surrounding the panel board, as the case may be (see No. 54.) When conduit is used every run of pipe must end in acces- LOW POTENTIAL SYSTEMS. 149 sible outlet boxes. This box may be a cutout center, switch outlet, fixture outlet or a junction box. If a mixed form of wiring is used, where part of a circuit is run in conduit and the balance with some other form of construction, such as concealed knob and tube work, for instance, the conduit must in all cases enter the box and be firmly attached to it, as shown in Figure 92.. Cases are sometimes found where the conduit is brought just to the box, but does not enter it, the Junction bo Figure 92 wires being extended through holes into the box. This method of wiring is obviously wrong; as a wireman is apt to find if he ever has occasion to replace wires in such a system. The same holds true of cutout centers. Here also every run of conduit must enter the box. The conduit should not simply be brought to the sides or the back of the cutout center and the wires then carried to the cutouts in flexible tubing, but every conduit should enter clear into the box so that when the work is completed there will be no exposed wiring. In 150 MODERN ELECTRICAL CONSTRUCTION. the case of main runs the conduit should enter the boxes and never be broken between the outlets. Sometimes it is neces- sary to install meters on the mains and the conduit is ended and the wires carried to the meters and then either extended in conduit or carried into the cutout center. This construc- tion should be avoided. If a meter is to be installed near a cutout center, the main conduit should be carried into the box and the necessary meter loops then brought out. In this way Figure 93 the quantity of wire outside of conduits is reduced to a mini- mum. If a meter is to be installed in some location along the mains other than at the cutout center or service switch, a junction box should be provided and the meter loops brought out from that. This is shown in Figure 93, which also shows a cutout box as used with conduit systems. c. Must be first installed as a complete conduit system, without the conductors. As fast as the conduit is installed, the ends of the pipes LOW POTENTIAL SYSTEMS. 151 should be closed, using paper or corks. This does away with the liability of plaster or other substances entering the pipes and causing trouble when the \vires are to be pulled in. The conductors shoilld not be pulled in until all the mechanical work on the building is, as far as possible, finished. When a con- duit system is ready for the wires, the "pulling in" may be done in various ways. For short runs, all that is necessary is to shove the wires in at one opening until they come out at the other. If a run is too long to be inserted in this way, what is known cs a "fish wire" can be used. The ordinary fish wire is a flat band of steel about 5/32 inch wide and 1/32 inch thick. This wire can be forced through any ordinary length of pipe. Ordinary round steel wire of about No. 12 or 14 B. & S. gauge can also be used for fish wire, although this is not as good as the fish wire above described. The end of the wire is first bent back so as to form a very small hook or eye; this will enable it to slide easily over ob- structions in the pipe and also make it possible should it stick somewhere to engage it with another fish wire provided with a suitable hook and entered from the other end of the pipe. This is very often necessary in runs having many bends. The fish wire, having been pushed through the pipe, is now fastened to the copper wire by means of a strong hook and the copper wire pulled into the pipe. In pulling in the large size cables, it is often found advan- tageous to pull on the fish wire and at the same time push on the end of the cable entering the pipes. It is also well to remember that it is easier to pull down than to pull up, as, when pulling down, the weight of the cable assists. The use of soapstone facilitates the drawing in of the wires. The wire may either be covered with the powdered soapstone or the soapstone may be blown into the pipes. An elbow partly filled with soapstone is often found convenient for blowing the soapstone into the pipe, always blowing from the highest point. 152 MODERN ELECTRICAL CONSTRUCTION. d. Must be equipped at every outlet with an approved out- let box or plate (see No. 49 /to 0). Outlet plates must not be used where it is practicable to install outlet boxes. In buildings already constructed where the conditions are such that neither outlet box nor plate can be Installed, these appliances may be omitted by special permission of the Inspec- tion Department having jurisdiction, providing the conduit ends are bushed and secured. The object of an outlet box is to hold the conduits firmly in place, to connect the various runs of conduit so that they form a continuous electrical path to the ground, and to afford a fireproof enclosure for the joints, switches, etc. Outlet boxes are made in various designs to meet the requirements of the work on which they are to be used. Where it is impossible to use an outlet box, an outlet plate can be used. These plates are fitted with set screws so that they hold the ends of the conduits firmly in position and make the metal of the system continuous. They do not afford a fireproof enclosure for the joints and for that reason should never be used when it is practicable to use an outlet box. If the conditions are such that neither an outlet box or plate can be used, special permission can be obtained from the Inspec- tion Department having jurisdiction to omit them. In this case the conduits should be bushed at the ends and the pipes should be bonded together. c. Metal conduits where they enter junction boxes, and at all other outlets, etc., must be provided with approved bushings fitted so as to protect wire from abrasion, except when such protection is obtained by the use of approved nipples, properly fitted in boxes or devices. When a piece of conduit is cut with a pipe cutter, a sharp edge is left on the inside. This edge, if left on, would soon cut into the insulation of the wires. It should be removed by means of a pipe reamer. The bushing can now be screwed on as shown in Figure 92, a locknut having first been screwed LOW POTENTIAL SYSTEMS. 153 onto the pipe. The locknut and bushing are then screwed up so that they are tight and .form a good connection. /. Must have the metal of the conduit permanently and effectually grounded. It is essential that the metal of conduit systems be joined so as to afford electrical conductivity sufficient to allow the largest fuse or circuit breaker in the circuit to operate before a dangerous rise in temperature in the conduit system can occur. Conduits and gas pipes must be securely fastened in metal outlet boxes so as to secure good electrical connection. Where boxes used for centers of distribution do not afford good electrical connections, the conduits must be joined around them by suitable bond wires. Where sections of metal conduit are installed without being fastened to the metal struc- ture of buildings or grounded metal piping, they must be bonded together and joined to a permanent and efficient ground con- nection. That the metal in a conduit system should be permanently and effectually grounded is plainly evident when the hazards which are present with ungrounded or poorly grounded con- duit are recalled. Until recently very little attention has been given to the matter of properly grounding conduits, but with the increased use the necessity of so doing has become very apparent. If the bare wire of one side of a system conies in contact electrically with the iron pipe, and if there is a ground on the other side of the system (and there always is with 3-wire systems) the conduit becomes a conductor. If the conduit system is so installed that every piece is in good electrical connection and the entire system effectually grounded no harm will be done except the blowing of a fuse. Conduit is installed in all kinds of locations. It may be in contact with a gas pipe, lead pipe, or run in a damp floor, or it may be run exposed where a person could easily come in contact with it. The effects that might result from a conduit so run should the conduit become alive are readily seen. Suppose that in the first case the conduit crosses the gas pipe at right angles, the area of contact would be very small and the effect of the cur- rent in a livened conduit crossing this poor contact would 154 MODERN ELECTRICAL CONSTRUCTION. result in burning a hole in the gas pipe and igniting the escap- ing gas. Again, suppose the conduit run in a damp floor should become alive ; the damp, wood work, being a conductor, would soon char and the charred part would then readily ignite. With a system which is grounded, an exposed piece of conduit will usually only be alive for a very short time during the blowing of the fuse. Even if it remains perma- nently alive, current will not flow from it to the surrounding material, but will take the easiest path to ground; which is along the conduit. On the ordinary branch circuits, the vari- ous runs of conduit are bonded together through the outlet boxes and, in connecting the conduits to these boxes, care must be taken that they make good contact. In order to do this, the conduit should enter at right angles to the box and the enamel should be scraped away from the box so that the locknut and bushing make good electrical connection. The same thing should be done where the conduit enters the cutout box. The metal of the cutout box will bond together the various branch conduits and the main conduit. The main conduit should now be connected to some good ground, such as a water or steam pipe or metal work of the building. Never carry the ground wire to a gas pipe. The various branch conduits should also be grounded wherever possible, at and on metal beams over which they cross and at every gas outlet. The reason of grounding the gas pipe thoroughly at the gas outlets is to be sure of a good ground. The gas pipe is necessarily in contact with the outlet box at this point and any poor contact which might cause arcing must be avoided. Strictly speaking, a conduit should be grounded with a wire equal to that usea in the conduit. This can easily be done in the case of smaller circuits, but with the larger size mains it is a more difficult matter. No special device has as yet been designed for the ground wire connection, the usual practice being to take a number of good turns around the conduit and LOW POTENTIAL SYSTEMS. 155 then solder the wire to the conduit and tape the joint. A better way would be to use a few T couplings on the system and to screw brass plugs to these and solder the ground wire to the plugs. Such couplings should be installed near outlets where they will not interfere much with "fishing." If the ground wire has to be run for any great distance, it should be installed as though it were at all times alive, and should be kept away from inflammable material. The method advised under 13 A for grounding wires should be used. Where a 3-wire system is used, the best ground obtainable is the neutral wire of the system. When a ground is made to the neutral wire, it should be made back of the fuses on the service switch ; never make the connection with the neutral inside of the service switch. g. Junction boxes must always be installed in such a manner as to be accessible. h. All elbows or bends must be so made that the con- duit or lining of same will not be injured. The radius of the curve of the inner edge of any elbow not to be less than three and one-half inches. Must have not more than the equivalent of four quarter bends from outlet to outlet, the bends at the outlets not being counted. If more than four quarter bends are necessary, a junction box should be installed and the wires first pulled from one of the outlets to the junction box and then from the junction box to the other outlet. Several methods are in use for bending conduit. With the lined conduit elbows and bends of various shapes can be obtained already bent, and it is much more satisfactory to use these, as considerable care must be exercised in making bends in order to keep the inside lining from coming loose from the pipe and causing trouble when ''pulling in." To prevent this a suitable spiral spring is sometimes inserted into the con- duit before bending. Plumbers working with lead pipe often use coarse sand to fill the pipe before bending. This is more 156 MODERN ELECTRICAL CONSTRUCTION. particularly useful with special conduits such as brass tubing, which is sometimes used in showcase or window work and classed with fixtures. With unlined conduits the bending is a simple matter, although here also care must be taken to see that the conduit does not bend flat. In a good bend the pipe retains its circular form throughout the bend, while, if the bend is poorly made, the pipe will assume an oval shape, flattening somewhat at the bend. The smaller size conduits can be bent in a common vise. This is best accomplished by gripping the pipe in the Figure 94 vise and making a small bend, then moving the pipe for a slight distance and bending again, and continuing until the desired shape is obtained. Another method which can be used on small pipes is shown at a in Figure 94, using a three or four foot length of gas pipe or conduit with an ordinary gas pipe T on the end. This is run over the conduit and gives sufficient leverage to make any bend. A simple device used for bending conduits is shown at b in Figure 94. This is constructed of metal, the wheel being grooved to fit the pipe. A similar device, minus the wheel and lever, may be made up of two blocks of wood firmly fastened to a work bench. The pipe can be bent around this by hand. For the larger size conduits, elbows can be obtained already bent. Connections between the various lengths of conduit are LOW POTENTIAL SYSTEMS. 157 made with the ordinary gas-pipe couplings. When the conduit comes from the factory each Jength of pipe is provided with a coupling at one end. (This practice is now being discon- tinued, the couplings being left off.) This coupling should be removed and the end of the conduit reamed out. The reaming should always be done so that there is considerable metal left at the end of the pipe, and it should never be carried so far as to leave only a sharp edge. If a thread is to be cut, it is good practice to take a couple of turns with the reamer after this has been done. The coupling can then be screwed on. When making the connection, the pipes should be screwed into the coupling so that the ends just "butt." Do not attempt to screw them too tight, or, in all probability, the thread on the end Figure 95 of the pipe will be turned in and close the opening. Figure 95, a, shows how a connection should be made. If lined con- duit is not properly reamed and is screwed too tight, the opening is often entirely closed or forced inward, as shown at b. It is often necessary, especially in making changes in old installations, to fit pieces between two pipes, neither one of which can be turned so as to draw them together. In such cases a long thread is cut on one piece of the pipe and the coupling run back on it ; when the pipes are butted together the coupling is run over the two pipes, thus connecting them. A locknut may be run upon either pipe and used to keep the coupling in place. In running conduits avoid as much as possible passing through bath-rooms and other places where plumbers are likely to run their piping. 158 MODERN ELECTRICAL CONSTRUCTION. When practicable, conduits should be run so they will drain ; for instance, where crossing a room from one side bracket to another, it is better to run along ceiling than along the floor. Conduits will sometimes become quite moist inside from con- densation. Where there is any likelihood of this the ends may be sealed. 26. Fixtures. (Sec also Nos. 22 e, 24 v to x.) a. Must when supported from the gas piping or any grounded metal work of a building be insulated from such piping or metal work by means of approved insulating joints (see No. 59) placed as close as possible to the ceiling. "Gas outlet pipes must be protected above the insulating joint by approved insulating tubing, and where outlet tubes are used they must be of sufficient length to extend below the insulating joint, and must be so secured that they will not be pushed back when the canopy is put in place "Where canopies are placed against plaster walls or ceilings in fireproof buildings, or against metal walls or ceilings, or plaster walls or ceilings on metallic lathing in any class of buildings, they must be thoroughly and permanently insulated from such walls or ceilings." Figure 96 shows insulating joints such as are used to insu- late fixtures from the gas piping of buildings. The object of an insulating joint is to prevent a "ground" Figure 96 on one fixture from causing trouble on other fixtures. If, for instance, one fixture in a building were in contact with the positive wire of the system and another in contact with a nega- tive wire, and the two fixtures connected direct to the gas LOW POTENTIAL SYSTEMS. 159 piping, the two contacts or "grounds" would form a short cir- cuit; the current flowing from one pole along the gas piping to the other. This becomes impossible when the fixtures are insulated from the piping, or conducting parts of ceilings. Insulating joints are made in a variety of patterns. The one shown at a in Figure 96 is designed for use on a combina- tion gas and electric fixture, and is made to allow the gas to pass through. Other forms, such as b, can be used on conduit work to connect to the stub in the outlet box, or on a gas outlet where it is desired to use the electric light only. Insulating joints should be placed as close as possible to the ceiling, so that there will be a minimum of exposed pipe above Figure 97 the joint. If the gas pipe has been left long so that the insu- lating joint comes some distance below the ceiling, it is a good plan to protect the pipe above the joint either by using a porce- lain tube which will fit over the pipe or by taping the pipe thoroughly. Flexible tubing is also sometimes used. See Figure 97. In connecting the fixture, care should be taken that the extra wire usually left for making the joint is twisted around the pipe below the insulating joint; never above. If the wires at the outlet have been properly run, as shown in Figure 97, the flexible tubing will extend to the bottom of the insulating joint. 160 MODERN ELECTRICAL CONSTRUCTION. When a straight electric fixture is to be installed on some grounded part of the building, a crowfoot, shown at c, Figure 96, can be fastened to the metal work and the fixture then con- nected with the insulating joint. If the fixture is to be mounted on plaster, a hardwood block can be screwed to the wall or ceiling and a crowfoot screwed to this. The screws holding the crowfoot must not extend through the block. Such a case is illustrated at the right in Figure 97. Before the plastering is put on, a board should be fastened between the joists, so that the wooden block may later be screwed to it. This is not absolutely necessary, as screws in lath will usually hold light fixtures. Heavy fixtures in old Figure 98 buildings can best be hung as shown at b, in Figure 98. This method is also used for ceiling fan motors. These motors must never be rigidly fastened, but should always be left free to swing and find their own centers. In connection with open or moulding work, the canopies should always be cut out, so that the loom or moulding may enter them. On no account should wires be allowed to rest on sharp edge of canopy. See a, Figure 98. Figure 98 illustrates at c how fixtures are fastened to tile ceilings, toggle bolts and a metal strip to which a piece of pipe is fastened being used. LOW POTENTIAL SYSTEMS. 161 Fiber is often used for the insulation of canopies from the ceiling. Figure 98 at d shows a bug insulator, which can be used for this purpose. A hole is drilled in the center of a small block of fiber, and it is then slotted lengthwise with a saw. A small dent is made in the upper edge of the canopy and the fiber blcck slipped on the edge, so that the small dent fits into the hole. If a hole is punched through the edge of the canopy, and a brass pin riveted in, a much better job is obtained. Short, thin strips of fiber, or a long strip riveted to the inside of the canopy and left to project about one-eighth inch, are often used. These being placed on the inside of the canopy are much more sightly than the bug insulators. When a wooden block is used to fasten the fixture to the wall, the block may be made large enough so that the canopy will fit against it. The practice of fastening the canopy a short dis- tance from the ceiling does not comply with the rule. b. Must have all burs, or fins, removed before the con- ductors are drawn into the fixture. c. Must be tested for "contacts," between conductors and fixture, for "short circuits" and for ground connections before it is connected to its supply conductors. Fixtures are always made up of gas piping and their con- struction is, therefore, very similar to conduit work. Three tests should be made on each fixture before it is con- nected. If tests are not made until fixtures have been con- nected, it is often necessary to disconnect them again to de- termine whether a fault is in the fixture or in the wiring. Where there are several fixtures on one circuit arid a short circuit should be discovered, it would also likely be necessary to disconnect several of them before the right one would be found. A test for short circuit may be made, first, by connecting the two wires of a magneto to the two main wires at top of fixtures. If all sockets are properly connected and the wiring 162 MODERN ELECTRICAL CONSTRUCTION. is clear, no ring will be obtained. If a ring is obtained, it indicates a short circuit. Without changing connections each socket may now be tested for connections. While one man is operating the mag- neto, another may insert a screw-driver, jack-knife, or piece of wire into each socket in turn, thus connecting the two termi- nals and causing a ring of the magneto. Failure to obtain a ring would indicate an open circuit, which must, of course, be remedied. The third test is made for "grounds." To make it, the two fixture wires are connected to one wire of the magneto and the other wire is connected to the metal of the fixture. It is best to connect this wire to the iron piping, and not to the lacquered brass ; the lacquer is often a very good insulator. If a ring is now obtained, it indicates that the insulation on a wire has been damaged, and that the bare wire is in contact with the fixture. This test can be made more thorough by working the accessible fixture wires back and forth during the test ; sometimes, a damaged portion of wire is not in contact with the metal of fixture while lying upon the floor, but may be brought in contact with it when hanging. Fixtures that have been connected to the circuit and pro- vided with insulating joints can be individually tested for "grounds," by connecting one wire of a magneto to the body of the fixture and the other, first to one, and then the other, of the circuit wires in the sockets. This test will detect a "ground" in a fixture without disconnecting it from the cir- cuit. In connecting sockets to fixtures, it is advisable to connect them so that all protruding parts, as keys or receptacles for lamps, be of the same polarity, that is, all connected to the same main wire. This also applies to reflectors, border lights for theaters, encased in metal, etc. This will not lessen the liability of such parts to "ground," but lessens the chances LOW POTENTIAL SYSTEMS. 163 of short circuits very much. Many "shorts" are brought about by the projecting brass lamp butts on fixtures being of opposite polarity. If they are of the same polarity, they will cause no trouble. Special fixtures for show windows, etc., are often made up as shown in Figure 99. The construction shown at the left is more compact and neat, but requires more care in installing Figure 99 than the other, because of the edges of pipe in contact with the wires. If very long fixtures of this kind are installed, it is advisable to insert insulating joints as often as practicable, even if necessary to run wires around them. 27. Sockets. (For construction rules, sec No. 55.) a. In rooms where inflammable gases may exist the incan- descent lamp and socket must be enclosed in a vapor-tight globe, and supported on a pipe-hanger, wired with approved rubber-covered wire (see No. 41) soldered directly to the circuit. In Figure 100, a shows a "vapor-tight" globe suspended on a pipe hanger, the construction of which complies with the requirements of this rule. If moisture is present it is well to seal the upper end of the pipe with compound. 164 MODERN ELECTRICAL CONSTRUCTION. b. In damp or wet places, or over specially inflammable stuff, waterproof sockets must be used. Waterproof sockets should be hung by separate, stranded, rubber-covered wires, not smaller than No. 14 B. & S. gage, which should preferably be twisted together when the pendant Is over three feet long. These wires should be soldered direct to the circuit wires, but supported independently of them. Waterproof sockets are constructed entirely of porcelain and are not provided with keys, therefore the circuits to which they are connected must be controlled by switches. As a gen- eral rule these sockets are furnished with a short piece of Figure 100 stranded, rubber-covered wire extending through sealed holes in the top of the socket and the supporting wires are soldered to them. The method of suspending waterproof sockets varies with the conditions. Ordinarily, stranded rubber-covered wires of the proper length are suspended from single cleats as shown at b, in Figure 100, or, if the line knobs are large enough, the stranded wire may be supported from them. If the lamp is to be suspended only a short distance from the LOW POTENTIAL SYSTEMS. 165 ceiling, where it will not be liable to be disturbed, it may be hung from two ordinary inch porcelain knobs, as shown in Figure 81. If cleats are used in a damp place for supporting the drop a half cleat must be provided back of the supporting cleat to give a one-inch separation, as required for wires in wet places. 28. Flexible Cord. a. Must have an approved insulation and covering (see No. 45). b. Must not be used where the difference of potential between the two wires is ove,r 300 volts. c. Must not be used as a support for clusters. d. Must not be used except for pendants, portable lamps or motors, and portable heating apparatus. The practice of making the pendants unnecessarily long and then looping them up with cord adjusters is strongly advised against. It offers a temptation to carry about lamps which are intended to hang freely in the air, and the cord adjusters wear oft the insulation very rapidly. For all portable work, including those pendants which are liable to be moved about sufficiently to come in contact with surrounding objects, flexible wires and cables especially de- signed to withstand this severe service are on the market, and should be used. (See No. 45 f.) The standard socket is threaded for one-eighth-inch pipe, and if it is properly bushed, the reinforced flexible cord will not go into it, but this style of cord may be used with sockets threaded for three-eghths-inch pipe, and provided with sub- stantial insulating bushings. The cable to be supported inde- pendently of the overhead circuit by a single cleat, and the two conductors then separated and soldered to the overhead wires. The bulb of an incandescent lamp frequently becomes hot enough to ignite paper, cotton and similar readily ignitible materials, and in order to prevent it from coming in contact with such materials, as well as to protect it from breakage, every portable lamp should be surrounded with a substantial wire guard. Flexible cord should be used only for drop lights which hang free in the air, or for desk lights or fan motors, where the cord is so installed that it is not liable to injury. Cord adjusters should never be used where their use can 166 MODERN ELECTRICAL CONSTRUCTION. be avoided and where they are installed should only be placed on lamps which will seldom need adjusting. The indis- criminate use of cord adjusters cannot be too strongly con- demned as the constant rubbing soon destroys the insulation. At c, Figure 100, shows a brass socket threaded for 5^-inch pipe, and which is designed to be used with portable cord. Care should be taken in making up these sockets to see that the knot under the head of the socket has a good bearing surface so that it will not pull through the larger bushing, these portables being very apt to be jerked about. A lamp guard to be of any value should be so constructed that the bulb of the lamp cannot come in contact with any- thing outside of the lamp guard; it should also protect the lamp from any sudden jar. The design of the guard should be such that it can be firmly attached to the socket so it will not work loose and come in contact with the live butt of the lamp or projecting threaded portion of the socket. c. Must not be used in show windows. The great number of fires which have been caused by the use of flexible cord in show windows is sufficient argument against its use. Portable cord, or what is kown as "show window" cord, should be used. /. Must be protected by insulating bushings where the cord enters the socket. g. Must be so suspended that the entire weight of the socket and lamp will be borne by knots under the bushing in the socket, and above the point where the cord comes through the ceiling block or rosette, in order that the strain may be taken from the joints and binding screws. Special ceiling blocks or rosettes which facilitate the fastening of cords are on the market and should be used. In fastening the cord to sockets the end of the cord should be soldered. This does away with the liability of stray strands short circuiting on the shell of the socket and also affords a LOW POTENTIAL SYSTEMS. 167 better and stronger contact under the binding screws. This soldering is best done by dipping the ends of the cord in melted solder. If a blow torch is used the small wires are very easily overheated and the soldering may do more harm than good. It is also well to tape the ends of cords, leaving only just enough bare metal to go under the binding screws ; the tape will hold the end of the braid and will confine any ends of wires which do not happen to come under the binding screws. 29. Arc Lamps on Constant-Potential Circuits. a. Must have a cut-out (see No. 17 a) for each lamp or each series of lamps. The branch conductors should have a carrying capacity about 50 per cent, in excess of the normal current required by the lamp to provide for heavy current required when lamp is started or when carbons become stuck without uverfusing the wires. Figure 101 at the left gives a diagram of a constant poten- tial arc circuit as generally used at present for enclosed arc lamps. Each arc lamp of this kind requires a pressure of 110 Figure 101 volts. A steadying resistance, R, is always placed in series with constant potential lamps, its object being to keep down the current while the lamp feeds. During the short time that the two carbons are together, the resistance of the lamp is so low that an enormous amount of current would flow were it not for this resistance. With most lamps this resistance is 168 MODERN ELECTRICAL CONSTRUCTION. now installed in the hood. Since the rule requires a carrying capacity about 50 per cent in excess of the normal current for branch conductors, it would be well to provide this also for mains in such cases where groups of arc lamps are likely to be controlled by one switch and used together. Figure 101 at the right shows a diagram of wiring for open arc lamps. Two lamps are usually run in series on 110 volts together with a steadying resistance. An open arc does not work well with a pressure higher than about 45 volts. b. Must only be furnished with such resistance or regula- tors as are enclosed in non-combustible material, such resist- ances being treated as sources of heat. Incandescent lamps must not be used for this purpose. c. Must be supplied with globes and protected by spark arresters and wire netting around the globe, as in the case of series arc lamps (see Nos. 19 and 58). Outside arc lamps must be suspended at least eight feet above sidewalks. Inside arc lamps must be placed out of reach or suitably protected. 30. Economy Coils. a. Economy and compensator coils for arc lamps must be mounted on non-combustible, non-absorptive insulating sup- ports, such as glass or porcelain, allowing an air space of at least one inch between frame and support, and must in gen- eral be treated as sources of heat. 31. Decorative Lighting Systems. a. Special permission may be given in writing by the Inspection Department having jurisdiction for the temporary installation of approved Systems of Decorative Lighting, pro- vided the difference of potential between the wires of any circuit shall not be over 150 volts and also provided that no group of lamps requiring more than 1,320 watts shall be de- pendent on one cut-out. No "System of Decorative Lighting" to be allowed under this rule which is not listed in the Supplement to the National Electrical Code containing list of approved fittings. LOW POTENTIAL SYSTEMS. 169 b. Incandescent lamps connected in series must not be used for decorative purposes inside of buildings except by special permission in writing from the Inspection Department having jurisdiction. 32. Car Wiring. a. Must always be run out of reach of the passengers, and must have an approved rubber insulating covering (see No. 41). 33. Car Houses. a. The trolley wires must be securely supported on insu- lating hangers. b. The trolley hangers must be placed at such a distance apart that, in case of a break in the trolley wire, contact cannot be made with the floor. c. Must have a cut-out switch located at a proper place outside of the building, so that all trolley circuits in the build- ing can be cut out at one point, and line circuit-breakers must be installed, so that when this cut-out switch is open the trolley wire will be dead at all points within 100 feet of the building. The current must be cut out of the building whenever the latter is not in use or the road is not in operation. d. All lamps and stationary motors must be installed in such a way that one main switch can control the whole of each installation lighting or power independently of the main feeder switch. No portable incandescent lamps or twin wire will be allowed, except that portable incandescent lamps may be used in the pits, the circuit to be controlled by a switch placed outside of the pit, and the connections to be made by two approved rubber-covered flexible wires (see No. 41), properly protected against mechanical injury. e. All wiring and apparatus must be installed in accord- ance with rules for constant-potential systems. f. Must not have any system of feeder distribution cen- tering in the building. g. The rails must be bonded at each joint with a con- 170 MODERN ELECTRICAL CONSTRUCTION. ductor having a carrying capacity not less than that of a No. 2 B. & S. gage annealed copper wire. h. Cars must not be left with the trolley in electrical con- nection with the trolley wire. 34. Lighting and Power from Railway Wires. a. Mast not be permitted, under any pretence, in the same circnit with trolley wires with a ground return, except in railway cars, electric car houses and their power stations; nor shall the same dynamo he used for both purposes. HIGH-POTENTIAL SYSTEMS. 550 TO 3,500 VOLTS. Any circuit attached to any machine or combination of ma- chines which develops a difference of potential, between any two wires, of over 550 volts and less than 3,500 volts, shall be considered as a high-potential circuit, and as coming under that class, unless an approved transforming device is used, which cuts the difference of potential down to 550 volts or less. 35. Wires. (Sec also Nos. 14, 15 and 16.) a. Must have an approved rubber-insulating covering (see No. 41). b. Must be always in plain sight and never encased, except where required by the Inspection Department having juris- diction. c. Must be rigidly supported on glass or porcelain insula- tors, which raise the wire at least one inch from the surface wired over, and must be kept about eight inches apart. Rigid supporting requires under ordinary conditions, where wiring along flat surfaces, supports at least about every four and one-half feet. If the wires are unusually liable to be disturbed, the distance between supports should be shortened. In buildings of mill construction, mains of No. 8 B. & S. gage or over, where not liable to be disturbed, may be separated about ten inches and run from timber to timber, not breaking around, and may be supported at each timber only. HIGH POTENTIAL SYSTEMS. 171 d. Must be protected on side walls from mechanical injury by a substantial boxing, retaining an air space of one inch around the conductors, closed at the top (the wires passing through bushed holes) and extending not less than seven feet from the floor. When crossing floor timbers, in cellars, or in rooms where they might be exposed to injury, wires must be attached by their insulating supports to the under side of a wooden strip not less than one-half an inch in thickness. For general suggestions on protection, see note under No. 24 e. See also note under No. 18 e. 36. Transformers. (When permitted inside buildings, see No. 13.) (For construction rules, sec No. 62.) (Sec also Nos. 13 and 13 A.) Transformers must not be placed inside of buildings with- out special permission from the Inspection Department having jurisdiction. a. Must be located as near as possible to the point at which the primary wires enter the building. b. Must be placed in an enclosure constructed of fire- resisting material ; the enclosure to be used only for this pur- pose, and to be kept securely locked, and access to the same allowed only to responsible persons. c. Must be effectually insulated from the ground, and the enclosure in which they are placed must be practically air- tight, except that it must be thoroughly ventilated to the out- door air, if possible, through a chimney or flue. There should be at least six inches air space on all sides of the transformer. 37. Series Lamps. a. No multiple series or series multiple system of light- ing will be approved. b. Must not, under any circumstances, be attached to gas fixtures. 172 MODERN ELECTRICAL CONSTRUCTION. EXTRA-HIGH-POTENTIAL SYSTEMS. OVER 3,500 VOLTS. Any circuit attached to any machine or combination of ma- chines which develops a difference of potential, between any two wires, of over 3,500 volts, shall be considered as an extra-high- potential circuit, and as coming under that class, unless an approved transforming device is used, zvhich cuts the difference of potential down to 3,500 -volts or less. 38. Primary Wires. a. Must not be brought into or over buildings, except power stations and sub-stations. 39. Secondary Wires. a. Must be installed under rules for high-potential sys- tems when their immediate primary wires carry a current at a potential of over 3,500 volts, unless the primary wires are installed in accordance with the requirements as given in rule 12 A or are entirely underground, within city, town and village limits. NOTICE DO NOT FAIL TO SEE WHETHER ANY RULE OR ORDINANCE OF YOUR CITY CONFLICTS WITH THESE RULES. CLASS D. FITTINGS, MATERIALS AND DETAILS OF CONSTRUCTION. ALL SYSTEMS AND VOLTAGES. Insulated Wires Rules 40 to 48 40. General Rules. a. Copper for insulated conductors must never vary in diameter so as to be more than two one-thousandths of an inch less than the specified size. b. Wires and cables of all kinds designed to meet the following specifications must be plainly tagged or marked as follows : 1. The maximum voltage at which the wire is designed to be used. 2. The words "National Electrical Code Standard." 3. Name of the manufacturing company and, if desired, trade name of the wire. 4. Month and year when manufactured. It Is recommended that all wires complying with these specifications be provided with a distinctive marking on the insulation or braid which will serve to identify them at any time. 41. Rubber-Covered Wire. a. Copper for conductors must be thoroughly tinned. 174 MODERN ELECTRICAL CONSTRUCTION. b. Must be of rubber or other approved substance, and of a thickness not less than that given in the following table : \ B. & S. Gage. Thickness. 18 to 16 ,..1-32 Inch. 15 to 8 3-64 " 7 to 2 1-16 " 1 to 0000 5-64 " Circular Mils. 250,000 to 500,000 3-32 " 500,000 to 1.000,000 7-64 " Over 1,000,000 . 1-8 " Measurements of insulating wall are to be made at the thinnest portion of the dielectric. c. The completed coverings must show an insulation resistance of at least 100 megohms per mile during thirty days' immersion in water at seventy degrees Fahrenheit. d. Each foot of the completed covering must show a dielectric strength sufficient to resist throughout five minutes the application of an electro-motive force of 3,000 volts per one sixty-fourth of an inch thickness of insulation under the following conditions : The source of alternating electro-motive force shall be a transformer of at least one kilowatt capacity. The application of the electro-motive force shall first be made at 4,000 volts for five minutes and then the voltage increased by steps of not over 3,000 volts, each held for five minutes, until the rupture of the insulation occurs. The tests for dielectric strength shall be made on a sample of wire which has been immersed in water for seventy-two hours. One foot of the wire under test is to be submerged in a conducting liquid held in a metal trough, one of the transformer terminals being connected to the copper of the wire and the other to the metal of the trough. Insulations for Voltages between 600 and 3,500 c. The thickness of the insulating wall must not be less than that given in the following table : B. & S. Gage. Thickness. 14 to 1 3-32 inch. to 0000 3-32 inch, covered by tape or braid. Circular Mils. 250,000 to 500,000 3-32 inch, covered by tape or braid. Over 500,000 1-8 inch, covered by tape or braid. FITTINGS, MATERIALS, ETC 175 f. The requirements as to insulation and break-down resistance for wires for low-potential systems shall apply, with the exception that an insulation resistance of not less than 300 megohms per mile shall be required. Insulation for Voltage over 3,500. g. Wire for arc-light circuits exceeding 3,500 volts poten- tial must have an insulating wall not less than three-sixteenths of an inch in thickness, and shall withstand a breakdown test of at least 30,000 volts and have an insulation of at least 500 megohms per mile. The tests on this wire to be made under the same condi- tions as for low-potential wires. Specifications for insulations for alternating currents ex ceeding 3,500 volts have been considered, but on account of the somewhat complex conditions in such work, it has so far been deemed inexpedient to specify general insulations for this use. Protecting Braid. h. All of the above insulations must be protected by a substantial braided covering, property saturated with a pre- servative compound. This covering must be sufficiently strong to withstand all the abrasion likely to be met with in practice, Figure 103 and sufficiently elastic to permit all wires smaller than No. 7 B. & S. gage to be bent around a cylinder with twice the diameter of wire, without injury to the braid. 42. Slow-burning Weatherproof Wire. (See Figure 103.) a. The insulation must consist of two coatings, one to be fireproof in character and the other to be weatherproof. The fireproof coating must be on the outside and must comprise 176 MODERN ELECTRICAL CONSTRUCTION. about six-tenths of the total thickness of the wall. The com- pleted covering must be of a thickness not less than that given in the following table: B. & S. Gage. Thickness. 14 to 8 3-64 inch. 7 to 2 1-16 1 to 0000. 5-64 Circular Mils. 250,000 to 500,000 3-32 500,000 to 1,000,000 7-64 Over 1,000,000 1-8 Measurements of insulating wall are to be made at the thinnest portion of the dielectric. This wire is not as burnable as "weatherproof," nor as sub- ject to softening under heat. It is not suitable for outside work. b. The fireproof coating shall be of the same kind as that required for "slow-burning wire," and must be finished with a hard, smooth surface if it is on the outside. c. The weatherproof coating shall consist of a stout braid, applied and treated as required for "weatherproof wire," and must be thoroughly slicked down if it is on the outside. 43. Slow-burning Wire. a. "The insulation must consist of layers of cotton or other thread, all the interstices of which must be filled with the fireproofing compound, or of material having equivalent fire Figure 104 resisting and insulating properties. The outer layer must be braided and specially designed to withstand abrasion. The thickness of insulation must not be less than that required for slow-burning weatherproof wire and the outer surface must be finished smooth and hard." "The solid constituent of the fireproofing compound must not be susceptible to moisture, and must not burn even when ground in an oxidizable oil, making a compound which, while proof against fire and moisture, at the same time has consider- FITTINGS, MATERIALS, ETC. 177 able elasticity, and which when dry will suffer no change at a temperature cf 250 F., and which will not burn at even a higher temperature. 44. Weatherproof Wire. (Sec Figure 104.) a. The insulating covering shall consist of at least three braids, all of which must be thoroughly saturated with a dense moisture-proof compound, applied in such a manner as to drive any atmospheric moisture from the cotton braiding, thereby securing a covering to a great degree waterproof and of high insulating power. This compound must retain its elasticity at deg. Fahr. and must not drip at 160 deg. Fahr. The thickness of insulation must not be less than that required for "slow-burning weatherproof wire," and the outer surface must be thoroughly slicked down. This wire Is for use outdoors, where moisture is certain and where fireproof qualities are not necessary. 45. Flexible Cord. (For installation rules, sec No. 28.) a. Must be made of stranded copper conductors, each strand to be not larger than No. 26 or smaller than No. 30 Figure 105 B. & S. gage, and each stranded conductor must be covered by an approved insulation and protected from mechanical injury by a tough, braided outer covering. For Pendant Lamps. (See Figure 105.) In this class Is to be included all flexible cord which, under usual conditions, hangs freely in air, and which is not likely to be moved sufficiently to ccme in contact with surrounding objects. It should be noted that pendant lamps provided with long cords, so that they can be carried about or hung over nails or 178 MODERN ELECTRICAL CONSTRUCTION. on machinery, etc., are not included in this class, even though they are usually allowed to hang freely in air. b. Each stranded conductor must have a carrying capacity equivalent to not less than a No. 18 B. & S. gage wire. c. The covering of each stranded conductor must be made up as follows : 1. A tight, close wind of fine cotton. 2. The insulation proper, which shall be waterproof. 3. An outer cover of silk or cotton. The wind of cotton tends to prevent a broken strand punc- turing the insulation and causing a short circuit. It also keeps the rubber from corroding the copper. d. The insulation must be solid, at least one thirty-second of an inch thick, and must show an insulation resistance of fifty megohms per mile throughout two weeks' immersion in water at 70 degrees Fahrenheit, and stand the tests prescribed for low-tension wires as far as they apply. c. The outer protecting braiding should be so put on and sealed in place that when cut it will not fray out, and where cotton is used, it should be impregnated with a flameproof paint, which will not have an injurious effect on the insulation. For Portables. (See Figure zoo".) In this class is included all cord used on portable lamps, small portable motors, or any device which is liable to be carried about. f. Flexible cord for portable use must meet all of the requirements for flexible cord "for pendant lamps," both as to Figure 106 construction and thickness of insulation, and in addition must have a tough braided cover over the whole. There must also be an extra layer of rubber between the outer cover and the flexible cord, and in most places the outer cover must be sat- urated with a moisture-proof compound, thoroughly slicked down, as required for "weatherproof wire" in No. 44. In FITTINGS, MATERIALS, ETC. 179 offices, dwellings or in similar places where the appearance is an essential feature, a silk cover may be substituted for the weatherproof braid. For Portable Heating Purposes. (Sec Figure 107.) g. Must be made up as follows : 1. A tight, close wind of fine cotton. 2. A thin layer of rubber or other cementing material about one one-hundreth of an inch thick. Figure 107 3. A layer of asbestos insulation at least three sixty- fourths of an inch thick. 4. A stout braid of cotton. 5. An outer reinforcing cover especially designed to with- stand abrasion. This cord is in no sense waterproof, the thin layer of rubber being intended merely to serve as a seal to help hold in place the fine cotton and asbestos, and it should be put on in such a way as will accomplish this. 46. Fixture Wire. (Sec Figure 108.) (For installation rules, sec No. 24 v to y.) a May be made of solid or stranded conductors, with no strands smaller than No. 30 B. & S. gage, and must hai~e a carrying capacity not less than that of a No. 18 B. & S. gage wire. b. Solid conductors must be thoroughly tinned. If a stranded conductor is used, it must be covered by a tight, close wind of fine cotton. r. Must have a solid rubber insulation of a thickness not less than one thirty-second of an inch for Nos. 18 to 16 B. & S. 180 MODERN ELECTRICAL CONSTRUCTION. gage, and three sixty-fourths of an inch for Nos. 14 to 8 B. & S. gage, except that in arms of fixtures not exceeding twenty- four inches in length and used to supply not more than one sixteen-candle-power lamp or its equivalent, which are so con- Figure 108 structed as to render impracticable the use of a wire with one thirty-second of an inch thickness of rubber insulation, a thickness of one sixty-fourth of an inch will be permitted. d. Must be protected with a covering at least one sixty- fourth of an inch in thickness, sufficiently tenacious to with- stand the abrasion cf being pulled into the fixture, and suf- ficiently elastic to permit the wire to be bent around a cylinder with twice the diameter of the wire without injury to the braid. e. Must successfully withstand the tests specified in Nos. 41 c and 41 d. 47. Conduit Wire. (For installation rules, see No. 24 n to p.) a. Single wire for lined conduits must comply with the requirements of No. 41 (Figure 109). For unlined conduits it must comply with the same requirements except that tape Figure 109 Figure 110 Figure 111 may be substituted for braid and in addition there must be a second outer fibrous covering, at least one thirty-second of an inch in thickness and sufficiently tenacious to withstand the abrasion of being hauled through the metal conduit. (Figures 110 and 111). b. For twin or duplex wires in lined conduit, each con- ductor must comply with the requirements of No. 41 except that tape may be substituted for braid on the separate con- FITTINGS, MATERIALS, ETC 181 ductors and must have a substantial braid covering the whole. For unlined conduit, each conductor must comply with require- ments of No. 41 except that tape may be substituted for braid and in addition must have a braid covering the whole, at least one thirty-second of an inch in thickness and sufficiently tenacious to withstand the abrasion of being hauled through the metal conduit (Figure 112). c. For concentric wire, the inner conductor must comply with the requirements of No. 41 except that tape may be substituted for braid and there must be outside of the outer conductor the same insulation as on the inner, the whole to be Figure 112 Figure 113 covered with a substantial braid, which for unlined conduits must be at least one thirty-second of an inch in thickness, and sufficiently tenacious to withstand the abrasion of being hauled through the metal conduit (Figure 113). The braid or tape required around each conductor in duplex, twin and concentric cables is to hold the rubber insulation in place and prevent jamming and flattening. 48. Armored Cable. (Sec Figure 114.) a. The armor of such cables must have at least as great strength to resist penetration of nails, etc., as is required for Figure 114 metal conduits (see No. 49 &), and its thickness must not be less than that specified in the following table : 182 MODERN ELECTRICAL CONSTRUCTION. Nominal Internal Diameter. Inches. Actual Actual Internal External Thickness Diameter. Diameter of Wall. Inches. Inches. Inches. .27 .40 .06 .36 .54 .08 .49 .67 .09 ' .62 .84 .10 .82 1.05 .11 1.04 1.31 .13 1.38 1.66 .14 1.61 1.90 .14 2.06 2.37 .15 2.46 2.87 .20 3.06 3.50 .21 3.54 4.00 .22 4.02 4.50 .23 4.50 5.00 .24 5.04 5.56 .25 6.06 6.62 .28 An allowance of two one-hundredths of an Inch for variation in manufacturing and loss of thickness by cleaning will be permitted. b. The conductors in same, single wire or twin conductors, must have an insulating covering as required by No. 41 ; if any filler is used to secure a round exterior, it must be impreg- nated with a moisture repellent, and the whole bunch of con- ductors and fillers must have a separate exterior covering. 49. Interior Conduits. (For installation rules, see Nos. 24 n to p and 25.) a. Each length of conduit, whether lined or unlined, must have the maker's name or initials stamped in the metal or attached thereto in a satisfactory manner, so that inspectors can readily see the same. The use of paper stickers or tags cannot be considered satis- factory methods of marking-, as they are readily loosened and lost off in the ordinary handling of the conduit. Metal Conduits with Lining of Insulating Material. (Sec Figure 1/5.) b. The metal covering or pipe must be at least as strong as the ordinary commercial forms of gas pipe of the same size, and its thickness must be not less than that of standard gas pipe as specified in the table given in No. 48. c. Must not be seriously affected externally by burning FITTINGS, MATERIALS, ETC. 183 out a wire inside the tube when the iron pipe is connected to one side of the circuit. d. Must have the insulating lining firmly secured to the pipe. c. The insulating lining must not crack or break when a length of the conduit is uniformly bent at temperature of 212 degrees Fahrenheit to an angle of ninety degrees, with a curve Figure 115 having a radius of fifteen inches, for pipes of one inch and less, and fifteen .times the diameter of pipe for larger sizes. /. The insulating lining must not soften injuriously at a temperature below 212 degrees Fahrenheit and must leave water in which it is boiled practically neutral. g. The insulating lining must be at least one thirty-second of an inch in thickness. The materials of which it is com- posed must be of such a nature as will not have a deteriorating effect on the insulation of the conductor and be sufficiently tough and tenacious to withstand the abrasion test of drawing long lengths of conductors in and out of same. h. The insulating lining must n^t be mechanically weak after three days' submersion in water, and when removed from/the pipe entire, must not absorb more than ten per cent of its weight of water during 100 hours of submersion. "/.'" All elbows or bends must be so made, that the con- duit or lining of same will hot be injured. The'. radius of. the curve of the 'inner edge of any elbow must not be less than three 'and one-half inches. Unlined Metal Conduits. (Sec Figure 116.) j. Plain iron or steel pipes of thickness and strengths equal to those specified for lined conduits in No. 49 b may be 184 MODERN ELECTRICAL CONSTRUCTION. used as conduits, provided their interior surfaces are smooth and free from burs. In order to prevent oxidation, the pipe must be galvanized, or the interior surfaces coated or en- Figure 116 ameled with some substance which will not soften so as to become sticky and prevent the wire from being withdrawn from the pipe. k. All elbows or bends must be so made that the conduit will not be injured. The radius of the curve of the inner edge of any elbow not to be less than three and one-half inches. Outlet Boxes. (Sec Figure 7/7.) /. Must be of pressed steel having a wall thickness not less than .081 in. (No. 12 B. & S. gage) or of cast metal hav- Figure 117 ing a. wall thickness not less than 0.128 in. (No. 8 B. & S. gage). m. Must be well galvanized, enameled or otherwise coated, inside and out, to pi event oxidation. FITTINGS, MATERIALS, ETC 185 . Inlet holes must be effectually closed when not in use by metal which will afford protection substantially equiv- alent to that of the walls of the box. o. Must be plainly marked where it will be seen when installed with the name or trade mark of the manufacturer. />. Boxes used with lined conduit must comply with the foregoing and in addition must have a tough and tenacious insulating lining firmly secured in position. 50. Wooden Mouldings. (Sec Figure 118.) (For wiring rules, sec No. 24, I and m.) a. Must have, both outside and inside, at least two coats of waterproof material, or be impregnated with a moisture repellent. b. Must be made in two pieces, a backing and a capping, and must afford suitable protection from abrasion. Must be so constructed as to thoroughly encase the wire and provide Figure 118 a one-half inch tongue between the conductors and a solid backing, which, under grooves, shall not be less than three- eighths of an inch in thickness. It is recommended that only hardwood moulding be used. 50A. Tubes and Bushings. (See Figure 118.) a. Construction. Must be made straight and free from 186 MODERN ELECTRICAL CONSTRUCTION. checks or rough projections, with ends smooth and rounded to facilitate the drawing in of the wire and prevent abrasion of its covering. b. Material and Test. Must be made of non-combustible insulating material, which, when broken and submerged for 100 hours in pure water at 70 degrees Fahrenheit, will not absorb over one-half of one per cenf of its weight. c. Marking. Must have the name, initials, or trade mark of the manufacturer stamped in the ware. d. Sizes. Dimensions of walls and heads must be at least as great as those given in the following table : Diameter External Thick- External Length Of Diameter. ness of Diameter of Hole. Wall. of Head. Head. Inches. Inches. Inches. Inches. Inches. 5/16 9/16 % 13/16 % % 11/16 5/32 15/16 % % 13/16 5/32 1 3/16 % % 15/16 5/32 1 5/16 % % 1 3/16 7/32 1 11/16 % 1 1 7/16 7/32 1 15/16 % IU 1 13/16 9/32 2 5/16 % 1% 2 3/16 11/32 2 11/16 % 1% 2 9/16 13/32 3 1/16 % 2 2 15/16 15/32 3 7/16 % 2% 3 5/16 17/32 3 13/16 1 2% 3-11/16 19/32 4 3/16 1 An allowance of one-sixty-fourth of an inch for variation in manufacturing will be permitted, except in the thickness of the wall. SOB. Cleats. (See Figure 118.) a. Construction. Must hold the wire firmly in place without injury to its covering. Sharp edges which may cut the wire should be avoided. b. Supports. Bearing points on the surface must be made by ridges or rings about the holes for supporting screws, in order to avoid cracking and breaking when screwed tight. c. Material and Test. Must be made of non-combustible insulating material, which, when broken and submerged for FITTINGS, MATERIALS, ETC. 187 100 hours in pure water at 70 degrees Fahrenheit, will not absorb over one-half of one per cent of its weight. d. Marking. Must have the name, initials or trademark of the manufacturer stamped in the ware. c. Sizes. Must conform to the spacings given in the fol- lowing table: Distance from Wire Distance between Voltage. to Surface. Wires. 0-300 Va inch. 2^ inches. This rule will not be interpreted to forbid the placing of the neutral of an Edison three-wire system in the conter of the three-wire cleat where the difference of potential between the outside wirer. is not over 300 volts, provided the outside wires are separated two and one-half inches. 50 C. Flexible Tubing. (Sec Figure 119.} The following specifications are designed to cover the construction of flexible tubes for fished v.-ork, loop system and for mechanical protection to wires where not exposed to moisture. Tubes complying with these requirements must not be used for a conduit system of wiring. a. Must be constructed to meet the following require- ments : Must have a sufficiently smooth interior surface to allow the ready introduction of the wire. Must be constructed of or treated with materials which will serve as moisture repellants. Figure 119 Must have a substantial outer covering especially de- signed to withstand abrasion. b. The linings must be secured in position so that they cannot be readily removed. 188 MODERN ELECTRICAL CONSTRUCTION. c. The tube must be thoroughly flexible at all temperatures at which it is to be used. d. Must not crack or break when kinked or flattened out. c. Must be sufficiently tough and tenacious to withstand severe tension without injury; the interior diameter must not be diminished or the tube opened up at any point by the appli- cation of a reasonable stretching force. /. Must not close to prevent the insertion of the wire after the tube has been kinked and straightened out, or flattened. g. Must not soften injuriously, or cause the wire to stick within the tube when subjected to a temperature of 150 degrees Fahrenheit. 51. Switches. (For installation rules, see Nos. 17 and 22.) General Rules. a. Must, when used for service switches, indicate, on in- spection, whether the current be "on" or "off." b. Must, for constant-current systems, close the main cir- cuit and disconnect the branch wires when turned "off" ; must be so constructed that they shall be automatic in action, not stopping between points when started, and must prevent an arc between the points under all circumstances. They must indicate whether the current be "on" or "off." Knife Switches (See Figure 120.) Knife switches must be made to comply with the following specifications, except in those few cases where peculiar design allows the switch to fulfill the general requirements in some other way, and where it can successfully withstand the test of Section i. In such cases, the switch should be submitted for special examination befcre being used. FITTINGS, MATERIALS, ETC. 189 c. Base. Must be mounted on non-combustible, non-ab- sorptive, insulating bases, such as slate or por- celain. Bases with an area of over twenty-five square inches must have at least four sup- porting screws. Holes for the supporting screws must be so located or countersunk that there will be at least one-half inch space, meas- ured over the surface, between the head of the screw or washer and the nearest live metal part, and in all cases when between parts of opposite polarity must be countersunk. d. Mounting. Pieces carrying the con- tact jaws and hir.gc clips must" be secured to the base by at least two screws, or else made with a square shoulder or provided with dowel- pins, to prevent possible turnings, and the nuts big. 120 or screw-heads on the under side of the base must be countersunk not less than one-eighth inch and covered with a waterproof compound which will not melt below 150 degrees Fahrenheit. c. Hinges. Hinges of knife switches must not be used to carry current unless they are equipped with spring washers, held by lock-nuts or pins, so arranged tha_t a firm and secure connection will be maintained at all positions of the switch blades. Spring washers must be of sufficient strength to take up any wear in the hinge and maintain a good contact at all times. /. Metal. All switches must have ample metal for stiff- ness and to prevent rise in temperature of any part of over fifty degrees Fahrenheit at full load, the contacts being ar- ranged so that a 'thoroughly good bearing at every point is obtained with contact surfaces advised for pure copper blades of about one square inch for each seventy-five amperes ; the whole device must be mechanically well made throughout. g. Cross-Bars. All cross-bars less than three inches in length must be made of insulating material. Bars of three inches and over, which are made of metal, to insure greater mechanical strength, must be sufficiently separated from the jaws of the switch to prevent arcs following from the con- 190 MODERN ELECTRICAL CONSTRUCTION. tacts to the bar on the opening of the switch under any cir- cumstances. Metal bars should preferably be covered with insulating material. To prevent possible turning or twisting the cross-bar must be secured to each blade by two screws, or the joints made with square shoulders or provided with dowel-pins. h. Connections. Switches for currents of over twenty- five amperes must be equipped with lugs, firmly- screwed of bolted to the switch, and into which the conducting wires shall be soldered. For the smaller sized switches simple clamps can be employed, provided they are heavy enough to stand considerable hard usage. Where lugs are not provided, a rugged double V groove clamp is advised. A set screw gives a contact at only one point is more likely to become loosened, and is almost sure to cut into .the wire. For the smaller sizes, a screw and washer connection with turned-up lugs on the switch terminal gives a satisfactory contact. i. Test. Must operate successfully at 50 per cent over- load in amperes and 25 per cent excess voltage, under the most severe conditions with which they are liable to meet in practice. This test is designed to give a reasonable margin between the ordinary rating of the switch and the breaking-down point thus securing a switch which can always safely handle its nor- mal load. Moreover, there is enough leeway so that a nimh-nite amount of overloading would not injure the switch. j. Marking. Must be plainly marked where it will be visible, when the switch is installed, with the name of the maker and the current and the voltage for which the switch is designed. k. Spacings. Spacings must be at least as great as those given in the following table. The spacings specified are correct for switches to be used on direct-current systems, and can therefore be safely followed in devices designed for alternating currents. 125 volts or less: Minimum Separation of Minimum Nearest Metal Parts of Break- Opposite Polarity. Distance. For Switchboards and Panel Boards 10 amperes or less .......... % inch. *& inch. 11-25 amperes .............. 1 " % 26-50 FITTINGS, MATERIALS, ETC. 191 For Individual Switches 10 amperes or less 1 inch. % inch. 11-35 . . 1 *4 ** 1 36-100 " . IV, " 114 101-300 " . . 21/i " 2 301-600 " 2% " 2% 601-1000 3 " 2% 126 to 250 volts: For all Switches 10 amperes or less 1% inch. 1*4 11-35 amperes 1% " \y 2 36-100 " 2Vi " 2 101-300 " 2% " 214 301-600 " .2% " 2% 601-1000 " 3 " 2% For 100 ampere switches and larger the above spacings for 250 volts direct current 'are also approved for 440 volts alter- nating current. Switches with these sparings intended for use en alternating-current systems with voltage above 250 volts must be stamped with the voltage for which they are designed, followed by the letters "A, C." 251 to 600 volts: For all Switches 10 amperes or less 3 V^ inch. 3 inch. 11-35 amperes 4 " 3 1 /. " 36-100 " 4'/6 " 4 " Auxiliary breaks or the equivalent are recommended for switches designed for over 300 volts and less than 100 amperes, and will be required on switches designed for use in breaking currents greater than 100 amperes at a pressure of more than 300 volts. For three-wire Edison systems the separations and break distances for. plain three-pole knife switches must not be less than those required in the above table for switches designed for the voltage between the neutral and outside wires. Snap Switches. (See Figures 121 and 122.) Flush, push-button, door, fixture, and other snap switches used on constant-potential systems, must be constructed in accordance with the following specifications. /. Base. Current-carrying parts must be mounted on non- combustible, non-absorptive insulating bases, such as slate or porcelain, and the holes for supporting screws should be coun- tersunk not less than one-eighth of an inch. There must 192 MODERN ELECTRICAL CONSTRUCTION. in no case be less than three sixty-fourths of an inch space between supporting screws and current-carrying parts. Sub-bases of non-combustible, non-absorptive insulating material, which will separate the wires at least one-half of Figure 121 an inch from the surface wired over, must be ftirnished with all snap switches used in exposed knob or cleat work. m. Mounting. Pieces carrying contact jaws must be se- cured to the base by at least two screws, or else made with a square shoulder, or provided with dowel-pins or otherwise arranged, to prevent possible turnings; and the nuts or screw heads on the under side of the base must be countersunk not less than one-eighth inch, and covered with a waterproof compound which will not melt below 150 degrees Fahrenheit. 11. Metal. All switches must have ample metal for stiff- ness and to prevent rise in temperature of any part of over Figure 122 50 degrees Fahrenheit at full load, the contacts being arranged so that a thoroughly good bearing at every point is obtained. The whole device must be mechanically well made throughout. FITTINGS, MATERIALS, ETC. 193 In order to meet the above requirements on temperature rise without causing excessive friction and wear on current- carrying parts, contact surfaces of from 0.1 to 0.15 square inch tor each 10 amperes will be required, depending upon the metal used and the form of construction adopted. o. Insulating Material. Any material used for insulating current-carrying parts must retain its .insulating and mechani- cal strength when subject to continued use, and must not soften at a temperature of 212 degrees Fahrenheit. />. Binding Posts. Binding posts must be substantially made, and the screws must be of such size that the threads will not strip when set up tight. q. Covers. Covers made of conducting material, except face plates for flush switches, must be lined on sides and top with insulating, tough and tenacious material at least one- thirty-second inch in thickness, firmly secured so that it will not fall out with ordinary handling. The side lining must ex- tend slightly beyond the lower edge of the cover. r. Handle or Button. The handle or button or any ex- posed parts must not be in electrical connection with the cir- cuit. s. Test. Must "make" and "break" with a quick snap, and must not stop when motion has once been imparted by the button or handle. Must operate successfully at 50 per cent overload in am- peres and 25 per cent excess voltage, under the most severe conditions with which they are liable to meet in practice. When slowly turned "on and off" at the rate of about two or three times per minute, while carrying the rated current, must "make and break" the circuit six thousand times before failing. t. Marking. Must be plainly marked, where it may be readily seen after the device is installed, with the name or trade mark of the maker and the current and voltage for which the switch is designed. On flush switches these markings may be placed on the back of the face plate or on the sub-plate. On other types they must be placed on the front of the cap, cover, or plate. Switches which indicate whether the current is on or "off" are recommended. 194 MODERN ELECTRICAL CONSTRUCTION. 52. Cut-Outs and Circuit-Breakers. (Sec Figure 123.) (For installation rules, sec Nos. 17 and . Sockets of Insulating Material. Sockets made of porcelain or other insulating material must conform to the 208 MODERN ELECTRICAL CONSTRUCTION. above requirements as far as they apply, and all parts must be strong enough to withstand a moderate amount of hard usage without breaking. Porcelain shell sockets being subject to breakage, and constituting a hazard when broken, will not be accepted for use in places where they would be exposed to hard usage. q. Inlet Bushing. When the socket is not attached to a fixture, the threaded inlet must be provided with a strong insulating bushing having a smooth hole at least nine thirty- seconds of an inch in diameter. The edges of the bushing must be rounded and all inside fins removed, so that in no place will the cord be subjected to the cutting or wearing action of a sharp edge. Bushings for sockets having an outlet threaded for three- eights-inch pipe should have a hole thirteen thirty-seconds of an inch in diameter, so that they will accommodate approved reinforced flexible cord. 56. Hanger-Boards. (See Figure 131.) a. Hanger-boards must be so constructed that all wires and current-carrying devices thereon will be exposed to view and thoroughly insulated by being mounted on a non-com- Figure 131 bustible, non-absorptive insulating substance. All switches attached to the same must be so constructed that they shall be automatic in their action, cutting off both poles to the lamp, not stopping between points when started and preventing an arc between points under all circumstances. FITTINGS, MATERIALS, ETC. 209 57. Arc Lamps. (See Figure 132.) (For installation rules, see Nos. 19 and 29.) a. Must be provided with reliable stops to prevent car- bons from falling out in case the clamps become loose. b. All exposed parts must be carefully insulated from the c. Must, for constant-current systems, be provided with an approved hand switch, and an automatic switch that will shunt the current around the carbons, should they fail to feed properly. The hand switch to be approved, if placed anywhere except on the lamp itself, must comply with requirements for switches on hangerboards as laid down in No. 56. 58. Spark Arresters. (Sec Figure 132.} (For installation rules, sec Nos. 19 c and 29 c.) a. Spark arresters must so close the upper orifice of the globe that it will be impossible for any sparks, thrown out by the carbons, to escape. Fig. 132. 59. Insulating Joints. (See No. 26 a.) a. Must be entirely made of material that will resist the action of illuminating gases, and will not give way or soften under the heat of an ordinary gas flame or leak under a mod- erate pressure. Must be so arranged that a deposit of moisture will not destroy the insulating effect ; must show a dielectric strength between gas-pipe attachments sufficient to resist throughout five minutes the application of an electro-motive force of 4,000 volts; and must be sufficiently strong to resist the strain to which they are liable to be subjected during instal- lation. 210 MODERN ELECTRICAL CONSTRUCTION. b. Insulating joints having soft rubber in their construc- tion will not be approved. 60. Rheostats. (For installation rules, see Nos. 4 a and 8 c.) a. Materials. Must be made entirely of non-combustible materials except such minor parts as handles, magnet insula- tion, etc. All segments, lever arms, etc., must be mounted on non- combustible, non-absorptive, insulating material. Resistance boxes are used for the express purpose of op- posing the passage of current, and are therefore very liable to get exceedingly hot. Hence they should have no combustible material in their construction. b. Construction. Must have legs which will keep the current-carrying parts at least one inch from the surface on which the rheostat is mounted. The construction throughout must be heavy, rugged, and thoroughly workmanlike. c. Connections. Clamps for connecting wires to the terminals must be of a design which will ensure a thoroughly good connection, and must be sufficiently strong and heavy to withstand considerable hard usage. For currents above fifty amperes, lugs firmly screwed or bolted to the terminals, and into which the connecting wires shall be soldered, must be used. Clamps or lugs will not be required when leads designed for soldered connections are provided. d. Marking. Must be plainly marked, where it may be readily seen after the device is installed, with the rating and the name of the maker; and the terminals of motor-starting rheostats must be marked to indicate to what part of the circuit each is to be connected, as "line," "armature," and "field." c. Contacts. The design of the fixed and movable con- tacts and the resistance in each section must be such as to secure the least tendency toward arcing and roughening of the contacts, even with careless handling or the presence of dirt. In motor-starting rheostats, the contact at which the cir- cuit is broken by the lever arm when moving from the running FITTINGS, MATERIALS, ETC. 211 to the starting position, must be so designed that there will be no detrimental arcing. The final contact, if any, on which the arm is brought to rest in the starting position must have no electrical connection. ui on tne arc, F. tend to spread it out and thus dissipate it f. No-voltage release. Motor-starting rheostats must be so designed that the contact arm cannot be left on interme- diate segments, and must be provided with an automatic device which will interrupt the supply circuit before the speed of the motor falls to less than one-third of its normal value. g. Overload-release. Overload-release devices which are inoperative during the process of starting a motor will not be approved, unless other circuit-breakers or fuses are installed in connection with them. If, for instance, the overload-release device simply releases the starting arm and allows it to fly hack and break the circuit, it is inoperative while the arm is being moved from the start- ing to the running position. h. Test. Must, after 100 operations under the most severe normal conditions for which the device is designed, show no serious burning of the contacts or other faults, and the release mechanism of motor-starting rheostats must not be impaired by such a test. Field rheostats, or main-line regulators intended for con- tinuous use, must not be burned out or depreciated by carrying the full normal current on any step for an indefinite period. Regulators intended for intermittent use (such as on electric cranes, elevators, etc.) must be able to carry their rated cur- rent on any step for as long a time as the character of the apparatus which they control will permit them to be used continuously. 61. Reactive Coils and Condensers. a. Reactive coils must he made of non-combustible material, mounted on non-combustible bases and treated, in general, as sources of heat. b. Condensers must be treated like other apparatus oper- ating with equivalent voltage and currents. They must have 212 MODERN ELECTRICAL CONSTRUCTION. non-combustible cases and supports, and must be isolated from all combustible materials and, in general, treated as sources of heat. 62. Transformers. {For installation rules, see Nos. n, is, 13 A and 36.) a. Must not be placed in any but metallic or other non- combustible cases. On account of the possible dangers from burn-outs In the coils. (See note under No. 11 a.) It is advised that every transformer be so designed and connected that the middle point of the secondary coil can be reached if, at any future time, it should be desired to ground it. b. Must be constructed to comply with the following tests : 1. Shall be run for eight consecutive hours at full load in watts under conditions of service, and at the end of that time the rise in temperature, as meas- ured by the increase of resistance of the primary coil, shall not exceed 135 degrees Fahrenheit. 2. The insulation of transformers when heated shall withstand continuously for five minutes a differ- ence of potential of 10,000 volts (alternating) be- tween the primary and secondary coils and be- tween the primary coils and core, and a no-load "run" at double voltage for thirty minutes. 63. Lightning Arresters. (For installation rules, see No. 5.) a. Must be mounted on non-combustible bases ; must be so constructed as not to maintain an arc after the discharge has passed ; must have no moving parts. CLASS E. MISCELLANEOUS. 64. Signaling Systems. Governing wiring for v telephone, telegraph, district mes- senger and call-bell circuits, fire and burglar alarms, and all similar systems. a. Outside wires should be run in underground ducts or strung on poles, and, as far as possible, kept off of buildings, and must not be placed on the same cross-arm with electric light or power wires. They should not occupy the same duct, manhole or handhole of conduit systems with electric light or power wires. Single manholes, or handholes, may be separated into sec- tions by means of partitions of brick or tile so as to be con- sidered as conforming with the above rule. b. When outside wires are run on same pole with electric light or power wires, the distance between the two inside pins of each cross-arm must not be less than twenty-six inches. c. All aerial conductors and underground conductors which are directly connected to aerial wires must be provided with some approved protective device, which must be located as near as possible to the point where they enter the building, and not less than six inches from curtains or other inflammable material. d. If the protector is placed inside of building, wires from outside support to binding-posts of protector, must comply with the following requirements: 1. Must be of copper, and not smaller than No. 18 B. & S. gage. 2. Must have an approved rubber insulating covering (see No. 41). 3. Must have drip loops in each wire immediately out- side the building. 4. Must enter buildings through separate holes sloping upward from the outside; when practicable, holes to be bushed with non-absorptive, non-combustible insulating tubes extending through their entire length. Where tubing is not practicable the wires shall be wrapped with two layers of insulating tape. 214 MODERN ELECTRICAL CONSTRUCTION. 5. Must be supported on porcelain insulators, so that they will not come in contact with anything other than their designed supports. 6. A separation between wires of at least two and one- half inches must be maintained. In case of crosses these wires may become a part of a high-voltage circuit, so that care similar to that given high- voltage circuits is needed in placing them. Porcelain bushings at the entrance holes are desirable, and this requirement is f nly waived under adverse conditions, because the state of t e art in this type of wiring makes an absolute requirement inadvisable. c. The ground wire of the protective device shall be run in accordance with the following requirements : 1. Shall be of copper, and not smaller than No. 18 B. & S. gage. 2. Must have an approved rubber insulating covering (see No. 41). 3. Must run in as straight a line as possible to a good, permanent ground, to be made by connecting to water or gas pipe, preferably water pipe. If gas pipe is used, the connection, in all cases, must be made between the meter and service pipes. In the absence of other good ground, connection must made to a metallic plate or bunch of wires buried in permanently moist earth. In attaching a ground wire to a pipe it is often difficult to make a thoroughly reliable solder joint. It is better, there- fore, where possible, to carefully solder the wire to a brass plug, which may then be firmly screwed into a pipe fitting. Where such joints are made under ground they should be thoroughly painted and taped to prevent corrosion. f. The protector to be approved must comply with the fol- lowing requirements : 1. Must be mounted on non-combustible, non-absorptive insulating bases, so designed that when the pro- tector is in place, all parts which may be alive will be thoroughly insulated from the wall to which the protector is attached. 2. Must have the following parts : A lightning arrester which will operate with a differ- ence of potential between wires of not over 500 volts, and so arranged that the chance of acci- dental grounding is reduced to a minimum. MISCELLANEOUS. 215 A fuse designed to open the circuit in case the wires become crossed with light or power circuits: The fuse must be able to open the circuit without arc- ing or serious flashing when crossed with any ordinary commercial light or power circuit. A heat coil, if the sensitiveness of the instrument de- mands it, which will operate before a sneak cur- rent can damage the instrument the protector is guarding. Heat coils are necessary In all circuits normally closed through magnet windings, which cannot indefinitely carry a current of at least five amperes. The heat coil is designed to warm up and melt out with a current large enough to endanger the instruments if con- tinued for a long time, hut so small that it would not blow the fuses ordinarily found necessary for such instruments. These smaller currents are often called "sneak" currents. 3. The fuses must be so placed as to protect the arrester and heat coils, and the protector terminals must be plainly marked "line," "instruments," "ground." g. Wires beyond the protector, except where bunched, must be neatly arranged and securely fastened in place in some convenient, workmanlike manner. They must not come nearer than six inches to any electric light or power wire in the building unless encased in approved tubing so secured as to prevent its slipping out of place. The wires would ordinarily be insulated, but the kind of insulation is not specified, ns the protector is relied upon to stop all dangerous currents. Porcelain tubing or approved flexible tubing may be .used for encasing wires where re- quired as above. h. Wires connected with outside circuits, where bunched together within any building, rr inside wires, where laid in conduits or ducts with electric light or power wires, must have fire-resisting coverings, or else must be enclosed in an air- tight tube or duct. It is feared that if a burnable insulation were used, a chance spark might ignite it and cause a serious fire, for many insulations contain a large amount of very readily burnable matter. 65. Electric Gas Lighting. a. Electric gas lighting must not be used or the same fix- ture with the electric light. 216 MODERN ELECTRICAL CONSTRUCTION. 65A. Moving Picture Machines. a. Top reel must be encased in an iron box with hole at the bottom only large enough for film to pass through, and cover so arranged that this hole can be instantly closed. No solder to be used in the construction of this box. b. A box must be used for receiving the film after being shown, made of galvanized iron with a hole in the top only large enough for the film to pass through freely, with a cover so arranged that this hole can be instantly closed. An opening may be placed at the side of the box to take the film out, with a door hung at the top, so arranged that it cannot be entirely opened, and provided with a spring catch to lock it closed. No solder to be used in the construction of this box. c. The handle or crank used in operating the machine must be secured to the spindle or shaft so that there will be no lia- bility of its coming off and allowing the film to stop in front of the lamp. d. A shutter must be placed in front of the condenser, arranged so as to be normally closed, and held open by pres- sure of the foot. e. A metal pan must be placed under the arc lamp to catch all sparks. f. Extra films must be kept in metal box with tight-fitting covers. 66. Insulation Resistance. The wiring in any building must test free from grounds; i. e., the complete installation must have an insulation between conductors and between all conductors and the ground (not including attachments, sockets, receptacles, etc.) not less than that given in the following table : Up to 5 amperes. 10 25 50 100 200 400 800 1,600 The test must be made with all cut-outs and safety de- vices in place. If the lamp sockets, receptacles, electroliers, etc.), are also connected, only one-half of the resistance speci- fied in the table will be required. . .4,000,000 ohms .2,000,000 . 800,000 . 400,000 . 200,000 . 100,000 50,000 25,000 12,500 PRACTICAL HINTS. 21? PRACTICAL HINTS. A full description of the Wheatstone bridge, the telephone, magneto and ether instruments, as well as the many ways of their application in testing for defects and for circuits in elec- trical installations having been given in a previous work of the authors (Wiring Diagrams and Descriptions} it is not thought necessary to repeat them here, especially as a work of this kind is necessarily limited in diagrams which would be re- quired to a full understanding of methods-. This chapter will, therefore, consist only of such hints and instructions as apply to general work. An electric light circuit may be tested for "short circuit" by connecting an incandescent lamp in place of one of the fuses. If the lamp burns while there are no lamps in circuit, there is sure to be a short circuit. A low candle-power lamp will indi- cate with less current than a high-candle-power lamp and is, therefore, better. If no lamp is available a small fuse should first be tried. A test for "ground" may be made in the same way, but the lamp must be connected to both sides in turn and the fuse left O/ in* 000000000000 Figure 133 out. If the main system to which the circuit to be tested con- nects is not grounded, a temporary ground must be put on. This is best done by connecting a lamp with one wire to a gas or water pipe and the other to the "live" binding screw on the opposite side of cutout to that in which the other lamp is con- nected. Thus, in Figure 133, if a ground should exist at 3 and the lamp be connected to gas pipe, as shown, the test lamp at 1 would burn. 218 MODERN ELECTRICAL CONSTRUCTION. If a voltmeter were connected in place of either of the lamps, the test would be much more searching. With 3-wire systems no ground need be put on, as the neu- tral wire will always be found grounded. The lamp need be tried in the outside fuses only. This test will be more search- ing if lamps are placed in all sockets connected. In placing fuses in the '3-wire, 110-220 volt system, the neu- tral wire should always be fused first. By reference to Figure 134 it will be seen that while the neutral fuse in main' blocks a is out, the two circuits of lamps c and d must burn in series; that is, just as much current must pass through one circuit as through the other. So long as there is an equal number of lamps in each circuit there is no trouble; but should most of the lamps in one circuit be turned off, those remaining would have to carry all the current that passes through the lamps of the other circuit. This current would overheat them and break, or burn them out in a very short time. If the neutral fuse is in place, each circuit is inde- pendent of the other and the neutral wire only carries the difference in current between the two sets of lamps. In order to insure against a neutral fuse "blowing" first in case of trouble, it is generally made heavier than in the outside wires. When a 3-wire circuit is to be cut off, the outside fuses should be drawn first. In order to find which is the "neutral" wire, two 110 volt lamps are connected in series and the wires from them brought in contact with two of the three wires. If both lamps burn at full candle power we have 220 volts, which is the pressure of the outside wires, and, therefore, the other wire must be the neu- tral. If the lamps burn only at half candle power, we have only 110 volts and one of the wires must be the neutral. That wire which gives 110 volts with either one of the other two wires is the neutral; this wire should always be run in the center between the other two. PRACTICAL HINTS. 219 A test for the neutral wire can also be made by connecting a lamp to ground. A lamp connected this way will burn from either of the outside wires, but not from the neutral. If the neutral wire should be connected to any but the middle binding post of 3-wire cutouts and the outside wire to the other two, one-half of the lamps would be almost imme- diately destroyed, being subject to 220 volts, while the other half would burn properly. If a short circuit occurs, say at c, Figure 134, on one side of a 3-wire system and blows the neutral fuse on that side of the circuit, we shall have 220 volts on the lamps on the oppo- site side. This will quickly burn them out. Most of these C 6 6 6 fe oooooooooooo a Figure 134 troubles are avoided to some extent by the use of such branch cutouts as shown. This confines trouble of this kind to the mains. On any system having a neutral wire or a wire on one side grounded, if a ground en either of the other wires occurs, the trouble can be temporarily remedied by simply changing the two wires of that circuit at the cutout. This will trans- fer the ground to the side already grounded, so that it will not interfere with operation. The ground must, however, be cleared up at once as no grounding is ever allowed inside of any building. When strip cutouts are set horizontally and there is no 220 MODERN ELECTRICAL CONSTRUCTION. bridge between opposite polarities, there will be the possibility of a partially melted upper fuse sagging down and forming a short circuit. On panel boards where fuses are set too close together, the heat of one fuse while blowing will often blow the next fuse above it. If large fuses are enclosed in small and very tight cabi- nets, the vapors formed by blowing will often cause short circuits. Before installing fuses in a "loaded" circuit, it is advisable to disconnect as many lights and other devices as possible. If there is a main switch this can easily be done. If there is no such switch on that part of the system, the task of placing fuses is somewhat hazardous ; for at the very instant that the second fuse touches its terminal a great rush of current will flow. If there happens to be a "short" on the line both fuses will probably blow and may burn the operator's hands and face severely. In order to avoid this, extremely careful manip- ulation is necessary. The first fuse can be placed without any difficulty, as there will be no current flow unless the cir- cuits are grounded. Before attempting to place the second fuse the circuits may be tested for "shorts" by placing a "jumper" (a piece of wire heavy enough so that it will not be heated by the current it is to carry) with the ends on the other fuse terminals. This "jumper" will complete the cir- cuit and, if all is in order the lights will burn. If there are two men, one may hold the jumper while the other places the fuse, but it should be placed as quickly as possible, especially if the circuit has a motor load, for these will be started very soon after the lights come on and will greatly increase the current. If there is but one man the jumper may be tem- porarily fastened to the mains. A jumper is not absolutely necessary even with large fuses, for if the last contact is made quickly and held steady, there PRACTICAL HINTS. 221 will be very little arcing; one should, however, provide all pro- tection possible. If a piece of asbestos is at hand, it may be used to cover the fuses, so as to protect the hands and face from melted metal. Before attempting to re-fuse a circuit, note condition of cutout block. If there is evidence of a great flash, it is very likely that the fuse was blown by a short circuit. If the blowing was caused by a slight overload or loose contact, the destructive effect will be much less. Much trouble can be prevented by cleaning terminals of fuse blocks occasionally and going over nuts and screws to see that they are tight. In Figure 135, a shows the proper way of connecting small wires into such terminals. This method prevents the screw from cutting into the main wire and allowing it to break. A wire should always be bent around the binding post of switch or cutout in the direction in which the nut which is to "b "C Figure 135 hold it must turn to be fastened as in c. If a wire is not long enough to be bent around the post or screw, a small piece of wire should be placed opposite it so as to give a level bearing to nut or washer. See b. Plug cutouts having their metal parts projecting above the porcelain, as shown at d, should be connected, whenever pos- sible, so that these metal parts are dead when fuses are with- drawn. This will prevent many accidental short circuits. The positive and negative wires of a circuit can easily be determined by immersing both wires in a little water, keeping 222 MODERN ELECTRICAL CONSTRUCTION. them an inch or so apart. Small bubbles will soon appear at the negative wire. If an arc lamp has been properly connected, the upper car- bon will be heated much more than the lower and will remain red longer. An arc lamp improperly connected is said to be burning "upside down" and will at once manifest itself by the strong light thrown against the ceiling. It is very often found necessary to determine the capacity of a cable which is already installed and where it is impossible to get at the separate wires of which it is formed. As cables are usually made up in a uniform manner, as shown in the table below, their capacity can be determined by the following method : To find the number of circular mils in a cable made up of wires of uniform size. Measure diameter of cable, count number of wires in outside layer, and, referring to the table below, find the same number in the first column ; divide the diameter of cable by the number set opposite this in the second column. This will give the diameter of each wire. Multiply this diameter by itself and then by the number 'of wires contained in cable as given in the third column. All measurements should be expressed in mils (1/1,000 inch) and the result will be the circular mils contained in cable. Outside layer 6 wires 3 times diameter 7 wires in cable 12 5 19 18 '7 37 " ii ii 24 9 " 61 " " 30 11 " " 91 " " 36 18 " 127 42 15 169 " " " The various figures in Figure 136 are designed to show how many single wires may be run in one conduit. Under each figure is given a number which, if multipled by the diameter of the wire to be used will give the smallest diameter of tube which can contain the corresponding number of wires. Thus, for instance, if 12 wires are run through PRACTICAL HINTS 224 MODERN ELECTRICAL CONSTRUCTION. one tube or conduit, the diameter of that conduit must be at least 4 1/3 times as great as the diame- ter of the wire to be used. Each figure illustrates the amount of spare room the corresponding number of wires leave, and it is necessary to use considerable judgment. Long runs will require more space, especially if the wires be quite large. Much also depends upon the nature of the insulation and the temperature. The figures are believed to be correct for single wires and can be followed for twin wires, as the same number of conductors arranged that way will not occupy as much space as single wires. The actual diameter of lined and unlined conduits are given in another table and may be referred to. The best way to accurately determine the diam- eter of small wire consists in cutting a number of short pieces and laying them together, then measuring over all and divid- ing the measurement by the number of wires. TRICKS OF THE TRADE. Cases have been known where it was requested to replace single pole switches by double pole, that the single pole switch was replaced as requested, but, instead of running both wires through it as required, only one wire had been properly brought into it and the other two binding posts filled out with short pieces of wire calculated to deceive the inspector. A test to detect this without disconnecting the switch is easily made. By reference to Figure 137 it will be seen that if a double pole snap switch is properly connected, current can be felt if the points a and b are touched with moistened fin- gers. If the switch is connected single pole, current can be felt at b and c, when the switch is open, only. On one occasion a wireman had run some wires on insu- lators along a ceiling and instead of soldering joints had care- THICKS OF THE TRADE. 225 fully, in many places above the joints, smoked the ceiling with a candle in order to deceive an inspector. In several cases where an "over-all" test of insulation re- sistance was made, meter loops which had been run in con- tinuous pieces were found with the wire "nicked" with a knife and then broken, leaving the insulation nearly intact, but the circuit open. A similar trick is often worked with the ground wire of ground detectors. In other cases plugs with fuses removed were put in "bad" circuits. In one case the real circuit wires (concealed Figure 137 Figure 138 work) were disconnected from cutouts and pushed back into the wall and short pieces connected instead. In another case where wire not up to requirements had been used and condemned, this wire, being run between joists and concealed by plastering, was pushed back and short pieces of approved wire stuck in at outlets. Sometimes in fished work after inspection the long pieces of loom reaching from outlet to outlet are withdrawn and short pieces at the outlets substituted. Lamp butts with wire terminals twisted together, or a strand of wire from lamp cord twisted around the base as shown in Figure 138 and screwed into the cutout are often used in place of fuses. The strand of cord is sometimes used to help out a fuse plug on an overloaded circuit. 226 MODERN ELECTRICAL CONSTRUCTION. Table cf Carrying Capacity of Wires. The following table, showing the allowable carrying ca- pacity of copper wires and cables of ninety-eight per cent con- ductivity, according to the standard adopted by the American Institute of Electrical Engineers, must be followed in placing interior conductors. For insulated aluminum wire the safe carrying capacity is eighty-four per cent of that given in the following tables for copper wire with the. same kind of insulation TABLE NO. I. Table A. Rubber Insulation. See No. 41. B. & S. G. Amperes. 18 3.... 16... 6... Table B. Other Insulations. SeeNos. 42 to 44. Amperes. Circular Mils. 5 1.624 8 2.583 14. 12 16 4 107 12 17. . . 6,530 10 8 24 33 46 . . 10,380 16 510 6 5 . 46 54. ... ... 65 77 . . 26,250 . . 33,100 4 3 65 76. . . 92 . 110... . . 41,740 . . 52,630 2 1 90 . 107 . 127. . . . ... 131 . . . 156 . . . 185 . . 66,370 . . 83,690 . .105,500 . .133,100 . .167,800 . .211,600 00 000 . 150 177 ... 220 262 0000 Circular Mils. 200,000 300,000 400,000 500,000 600,000 700,000 . 210 . 200 . 270 . 330 . 390.... . 450 . 500. . . . ... 312 . 300 ... 400 ... 500 . ... 590 ... 680 760 840 ... 920 1,000 080 150 800,000 900,000 1,000,000 1,100,000 1,200,000. . . . 550 . 600.... . 650 . 690 . 730... 1 300 000 770 220 1,400,000 1,500,000 1 600 000 . 810 . 850 890 290 1,360 430 1,700.000 1,800,000 1,900,000 2,000,000 . 930 . 970 .1,010 .1,050 490 550 610 ....1,670 TABLES. 227 The lower limit 5s specified for rubber-covered wires to prevent gradual deterioration of the high insulations by the heat of the wires, but not from fear of igniting the insulation. The question of drop is not taken into consideration in the above tables. The carrying capacity of Nos. 16 and 18, B. & S. gage wire is given, but no smaller than No. 14 is to be used, except as allowed under Nos. 24 v and 45 b. WIRING TABLES. The wiring tables, II-VI, are arranged in the following manner: For each size of wire and voltage considered there is given (under the proper voltage and opposite the number of the wire under the heading B. & S.) the distance it will carry 1 ampere at a loss designated at top of page. The same wire will carry 2 amperes only half as far at the same percentage of loss and again will carry I ampere twice as far at double the percentage of loss. From these facts we deduce the rule of these tables, which is: Multiply the distance in feet (one leg only) by the num- ber of amperes to be carried. Take the number so obtained and under the proper voltage find the number nearest equal to it. Opposite this number, under the heading B. & S., will be found the size of wire required. To illustrate : We have 22 amperes to carry a distance of 135 feet and the loss to be al- lowed is 3 per cent at 110 volts. We therefore multiply 135 X 22 = 2970, and turning to table TV., which is figured for 3 per cent loss, follow downward in the column under 110 until we reach the number nearest equal to 2970, which, in this case, is .3180 corresponding to a No. 7 wire. With this wire our loss will be slightly less than 3 per cent, while with No. 8 it would be somewhat in excess of 3 per cent. For three-wire systems using 110 volts on each side the column marked 220 volts should be used. The column marked 440 volts is provided for three-wire systems using 220 volts 228 MODERN ELECTRICAL CONSTRUCTION. on each side. The sizes determined will be correct for all three wires in both cases. The columns at the right, marked motors, are arranged in the same way, the only difference being, for greater con- venience, they are figured in horse-power feet instead of am- pere feet. For this reason we multiply the distance in feet by the number of horse-power to be transmitted and divide by tfie percentage of loss, all other operations remaining the same as under lights. When any considerable current is to be carried only a short distance the wire indicated by the de- sired loss will very likely not have sufficient carrying capacity ; it is, therefore, always necessary to consult the table of carry- ing capacities. RULE FOR WIRING TABLES. For lights, find the ampere feet (one leg) and under the proper voltage find the number equal to this or the next larger; opposite this number, in the column marked B. & S., will be found the size of wire required. For motors, proceed in the same way, using horse- power feet instead of ampere feet. For alternating currents, the results obtained by multi- plying the amperes (or horse-power) by the feet, should be multiplied by the following factors: 1.1 for single-phase systems, all lights. 1.5 for single-phase systems, all motors. For two-phase, four-wire, or three-phase, three-wire systems, each wire need be only one-half as large as for single-phase systems and the number obtained may, there- fore, be divided by two. 229 PI 58888 t-oo w o * o * -Ht^-Hwr^cc ^ fcWsM 9 -i rt rt ^ -4 M ., o^oosoi -Hooao 5?1S25 S5S '- S^ttSw S5*S2 M*^1K S5 SS2K5S ~--MOI co-^iot-ao i-r^Nao OfJ^r-^ ^OCWUS^IN 5So IslsS ^*i* wowt2 w^S^SS " - rt!NiN " ^5r:i2 33|g| liligB 1N ' HO SS r-< rtrt?3' illii! SS gi SS'{: feSSSSS "SSKS oowajia* cxcM"--; 1-071'- = - QO^XOO * SS88 a -HU^-^CO XC !o?l ^SroSit^ 3? toxog-' 230 MODERN ELECTRICAL CONSTRUCTION. ii SBH OOOCiNO 10 1^ oo ^ ^ Ic? -0 OJOOt^COUS -fMIN-0 ~ -^-f .::-!- ISSZZi ;= 231 SSS C^ .MT^^C O OOOU5- x-rn c-i -~-^f.^ ~i~i -s.-r ^ -f O X CO O ^ 'C 'T '-D 1^ O ^ C ! ~ * '-1 - 1 C coooo cor^-nf*-^ M'f - i CO rf co iN O rtr-^H^CO-O )Ooo oco^-^o cofNcoxo ocr^^jrCTj 1 -r^^r^-rx 232 111 MODERN ELECTRICAL CONSTRUCTION. c^ "^ gg s o w w r^- "< '- e 8? OOO mil nils III *3z? S'^oo oo 233 1*$ ^o 2s g; ^ rtrt(N CMMNCOtt, = = - --, - H O-nCirccO ^-31 l~~t~ rC-MC/"!- F-H^ ^MC^Mrtl USt^OO-H'J" OCM3CWO 1^ I-'- 1-trH TC^IC^CC-^ ^lOCC^It^ ^ p 5 fi S 00 ^ 5 S ?\ -N x x x ^r iC fC ! S ;; ^ S 2t;?ISM ^Ic^xo 2i>:2~f|^ *COQ4 O !|| S{ x ^i -N -^ i^ 7 ) 2 S |>4 57-64x107-64 00 41-64 46-64 ! 47-64 1 53-64 46-64x 87-64 53-64x 99-64 38-64 43-64 42-64 46-64 43 64x 81-64 46-64x 88-64 1 35-64 40-64 39-64 43-64 40-64x 75-64 43-64x 82-64 2 33-64 38-64 36-64 40-64 38-64x 71-64 40-64x 76-64 3 31-64 36-64 34-64 38-64 ' 36-64x 67-64 38-64x 72-64 4 29-64 ! 33-64 31-64 35-64 i 33-64x 62-64 35-64x 66-64 5 28-64 32-64 32-64x 60-64 6 27-64 31-64 28-64 32-64 31-64x 58-64 32-64x 60-64 8 24-64 28-64 26-64 30-64 28-64x 52-64 30-64x 56-64 10 22-64 26-64 24-64 28-64 26-64x 48-64 28-64x 52-64 12 21-64 25-64 22-64 26-64 25-64x 46-64 26-64x 48-64 14 20-64 24-64 21-64 25 64 24-64x 44-64 25-64x 46-64 mam these dimensions as me panic size wuc u- o often varies considerably in outside diameter. 238 MODERN ELECTRICAL CONSTRUCTION. Outside Diameters of Rubber Covered Cables. Capacity in Cir. Mils. Diameter over Braid 1,500,000 113-64 1,250,000 107-64 1,000,000 97-64 950,000 95-64 900,000 94-64 850,000 93-64 800,000 89-64 750,000 87-64 700,000 83-64 650,000 81-64 600,000 79-64 550,000 76-64 500,000 73-64 450,000 68-64 400,000 66-64 350,000 64-64 300,000 61-64 250,000 59-64 Dimensions of Unlined Conduit. Nominal Internal Actual Internal Actual iThick- External 'ness of Diam. Diam. Diam. Walls Inches. Inches. Inches. Nearest 64th 17-64 26-64 4-64 23-64 35-64 5-64 31-64 43-64 6-64 40-64 54-64 6-64 52-64 67-64 7-64 67-64 84-64 8-64 i 88-64 106-64 9-64 H 103-64 122-64 9-64 2 132-64 152-64 10-64 5ft 157-64 184-64 13-64 3 196-64 224-64 13-64 Outside Diameters of Weather- proof Wire. Size of Wire Outside Diameters. Solid Stranded i fwin fwv^ 1 ,IHH),UUU 900,000 10864 103-64 M )(),()( III 100-64 700,000 94-64 t O( I (MM) QC_J sooiooo S.) h-1 80-64 450,000 76-64 400,000 73-64 350,000 64-64 300,000 62-64 .'.-,( l.i i( Id 58-64 0000 50-64 55-64 000 47-64 51-64 00 39-64 43-64 36-64 39-64 32-64 35-64 2 30-64 33-64 3 27-64 30-64 4 25-64 28-64 5 22-64 24-64 6 20-64 22-64 8 17-64 18-64 10 16-64 12 14-64 14 12-64 16 10-64 18 8-64 Dimensions of Lined Conduit Nominal Internal Diameter Inches Actual Internal Diameter Inches Actual External Diameter Inches F I 1 32-64 45-64 58-64 80-64 90-64 115-64 144-64 176-64 54-64 67-64 84-64 106-64 122-64 152-64 184-64 224-64 TABLES. DIMENSIONS OF PORCELAIN KNOBS. 239 Trade No. Height Diameters H ole Groove H $ htof ire I* 3 2J ] - i " 1 i 2 2 2 ; : 3 11 2 j 3i 2 2 ! 4 ft 1* 5 1 i* 5J JL i 7 J z 9 | 1 .. 10i 1 it DIMENSIONS OF GLASS KNOBS. Trade Number Keif 1 i] ii 2 2 3] 'ht Width Size of Hole Size of Groove j 1 7 8 f 2 2J 1" cable SIZES OF PORCELAIN TUBES. Internal Diameter Inches Shortest Length Obtainable Greatest Length Obtainable Outside Diameter f | 1 1< 24 24 24 24 24 24 1 11 2< 24 IT~$ i! 2^ 94 2-j^- ii 2^ 24 2iV 2 f 2^ 24 2H 2J 2^ 2^ 24 3U DIMENSIONS OF MOULDINGS. Siz B of Groove Size of Wire Size of Groove 7-32 5-16 13-32 9-16 14-12 B. & S. 10- 8 B. & S. 6-5-4 B. & S 32 1-0 B. & S. 3-4 7-8 1 1 1-4 0-0000 Stranded 250.000 C. M. 500.000 C. M. 750. 000 C. M. 240 MODERN ELECTRICAL CONSTRUCTION. DIMENSIONS OF CLEATS. ONE-WIRE CLEATS. DUOGAN CLEAT. No. 4 holds wires 16-8 B. & S. No. 7 - " 6-2 " No. 5 " " 2-00 No. 6 " " 000-300,000 C M. No. 8 " " 400.000-800,000 C. M. No. " " 900,000- 1, 200,000 C. M. BRDNT CI.EAT. Stand. Number Width Length Groove 328 | 2 < holds wires 16-5 B. & S 329 1 2i i "' " 8-3 331 if 2| H " " 3-00 330 1J 2} i " " 4-1 332 11 21 H " " 0-0000 Two AND THREE-WIRE CLEATS. BHONT. No. 334 2-wire holds wires 16-8 B. & S- No. 337 3 wire " " 16-8 B. & S DOOGAN. No. 3 2-wire holds wires 16-8 B. & 8. No. 2 2-wire " " ' 6-00 B. & S. No. 1 3 wire " ... 16-8 B. & S. PASS & SEYMOUR. No. A-3 2-wire holds wires 14-12 B. & S.j No. 3 2-wire " " 14- 6 B. & 8- No. A-43 3-wire " " 14-12 B. & S. No. 43 3-wire " ... 14- 6 B. & 3. APPROXIMATE. Trade Numbe Diameter in fractions ri. 3 V | r 5 A 6 7 iYi 8 rira 9 in n JU 11 II 12 14 13 14 np 15 i 4 16 * 17 94 18 1 DIMENSIONS OF COMMON NAILS. APPROXIMATE. Trade Number Diameter in Fractions Nearest B. & S. Gauge Length in N . Inches per lb 2d 3d ill 13 1 crc 4d w 12 U 565 5d y 18 6d y 10 U ; '70 7d 8d 9 ^ ifO 9d lOd s 8 8 22 105 95 12d J l 7 70 Ifld nn C 3} 60 20d ft 6 3i 50 1 4 4 30 FINE NAILS 242 MODERN ELECTRICAL CONSTRUCTION. RATING OF MOTORS. FULL LOAD CURRENTS. H. P. 110 VOLTS 220 VOLTS 500 VOLTS 1 9 .95 .42 2 7 1.35 .62 5. 2.50 1.15 7.5 9.2 3.75 4.60 1.70 2.10 2 3 4 5 7i 17.5 24.6 32. 40. 57. 8.75 12.30 16. 20. 28.5 4. 5.60 7.50 9.^0 13. 10 15 20 76. 110. 144. 38. 55. 72. 17.5 25. 34. 25 30 176. 210. 88. 105. 49. 35 40 45 250. 280. 320. 125. 140. 160. 57. 65. 75. 50 60 350. 430. 175. 215. 100. 75 100 125 150 520. 700. 880. 1056. 260. 350. 440. 530. 120. 160. 210. 245. 175 200 1230. 1400. 615. 700. 325. RATING OF INCANDESCENT LAMPS. 110 VOLTS 220 VOLTS C. P. Watts Amperes C. P. Watts Amperes 4 18 .16 8 36 .16 6 8 10 12 16 20 24 30 35 40 56 70 .22 .27 .32 .36 .51 .64 10 16 20 24 32 50 45 64 76 90 122 190 .29 .35 .41 .55 .86 24 84 .76 32 112 1.00 50 175 1.60 TABLES. 243 The Hewitt-Cooper Mercury Vapor lamp requires a current of about 2.5 amperes. The Nernst lamp consumes 88 watts per glower; for a 6 glower, 110 volt lamp, about 4.8 amperes. Series miniature lamps, operated 8 in series, on 110 volts, require a current of about .33 amperes for 1 candle power lamps, and 1 ampere for 3 candle power lamps. Tables showing the currents which will fuse wires of different sub- stances. B. &S. Gauge Hiai.i. Copper Aluminum German Silver Iron 10 102. 333. 246.5 170. 102.3 12 81. 236. 174.4 120.5 72.6 14 64. 165.7 122.8 84.6 50.9 16 51. 117.7 87.1 60.1 36.1 18 40. 81.9 60.7 41.8 25.2 20 32. 58.5 43.4 29.9 18. 22 25.3 41.1 30.5 21.0 12.4 24 20. 28.9 21.5 14.8 8.9 26 16. 20.7 15.3 10.6 0.4 28 12.6 14.5 10.7 7.4 4.5 30 10. 10.2 7.6 5.2 3.1 32 8. 7.3 5.4 3.7 2.3 34 6.3 5.1 3.8 2.6 1.6 36 5. 3.6 2.7 1.8 1.1 INDEX Page. J-13 Acid Fumes 76-137 Alternating Current System :55 Amperes 13 Arc Lamps, Construction of 209 Arc Lamps, Installation of 108-113-167 Arc Lamp Switches 109 Armored Cable 181 Base Frames, Generators and Motors 47-63 Batteries, Storage or Primary 27-76 Bells 19 Binding Screws, Not to Bear Strain 166 Bonds, Rails in Car Houses 169 Boxing, Where Necessary 111-133-171 Burrs and Fins, Fixture Work 161 Bushings for Wires 97-185 Bushings, Lamp Sockets 166 Bus Bars 52-54 Cabinets for Cut-Outs 123-202 Cable, Armored 181 Calculation of Wires 40 Care and Attendance 59 Car Houses 169 Carrying Capacity Table 226 Car Wiring 169 Ceiling Fans 75-160 Central Stations 47 Circular Mil 40 Circuit Breakers, Construction of 194 Circuit Breakers, Installation of 51-73-76-105-114-123 Circuit, Open 9 Circuit, Closed 9 Circuits, Divided 16 Cleats 93-186 Compensator Coils 168 Conductors 10 Concealed Wiring 98-128-131-138 Condensers 211 Conductors ( See Wires) Conduits, Installation of 147 Conduits. Lined Metal 182 Conduits, To Be Marked 182 Conduits, Unlined Metal 183 r-ondults. Wire for 180 Conduit Work 141 Constant Current Systems 32-108 INDEX Constant Potential Systems... g Electric Gas Lighting . 215 Electric Heaters 129 Electro-Magnetic Devices for Switches 114 Electro-Motive Force 11 Electrolysis 100 Equalizers 50 Extra High Potential Systems 172 Feeders, Railway 1GO Fished Wires 133-142 Fittings and Materials 373 Fixtures 158 Fixture Wire .179 Fixture Wiring 14(5 Flexible Cord, Construction of 117 Flexible Cord, Construction of. Heaters 179 Flexible Cord, Construction of, Pendants 178 Flexible Cord, Construction of, Portables 178 Flexible Cord. Use of 105 Flexible Tubing 142 Foreign Currents, Protection Against 213 Formula for Soldering Fluid 95 Fuses, Construction of 199 Fuses, Installation of 114-221 Gas Liehting. Electric 215 Generators 47 Ground Connections 90-154 Ground Detectors 59-62 Grounded Trolley Circuits 170 Ground'ng Low Potential Circuits 88 Grounding of Dynamo and Motor Frames 47-63 Grounds. Testing for 59 Ground Wire for Lightning Arresters 57-213 Hanger Boards, Construction of 208 Haneer Boards. When Not Used 113 Heaters. Electric High. Constant Potential Systems 170 ii INDEX Incandescent Lamps as Resistances 56-168 Incandescent Lamps in Series Circuits 114-168 Induction Coil 25 Inside Work 92 Insulators 10 Insulating Joints, Construction of 209 Insulating Joints, When Required 158 Insulation of Trolley Wires 82 Insulation Resistance 61-216 Interior Conduits (See Conduit) Joints in Conductors 80-93 Joints, Insulating (See Insulating Joints) Knob and Tube Work 03 >nmps, Arc (See Arc Lamps) .;i nips. Incandescent Series 114-168 ,ightnlng Arresters, Construction of 212 >ightning Arresters, Installation of ' 57 ights from Trolley Circuits 170 oop System 143 Low Potential Systems 131 Mechanical Injury, Protection Against 111-133-171 Motors 63 Moulding, Construction of 185 Moulding Work 138 Moving Picture Machines 216 Multiple Series System 34-74 Ohms Law 13 Ohm 12 Oily Waste 59 Open Wiring 135 Outlet Boxes 149-184 Outside Work 78-83-86-88 Panel Boards 201 Picture (Moving) Machines 216 Pole Lines 81 Portable Conductors 178 Power 14 Power from Trolley Circuits 170 Practical Hints 217 Protective Devices, Signal Circuits 213 Railway Power Plants , 76 Reactive Coils 211 Reinforcing Wires 120 Resistance 12-41 Resistance Boxes, Construction of 210 resistance Boxes, Installation of 55 "'sistar-ce for Arc Lamp, Low Potential 168 Rheostats (See Resistance Boxes) in INDEX Sag in Outside Wires 79 Series Arc System :...., 32 Series Lamps IRQ 171 Series Multiple System ." 35.74 Service Blocks and Wires 78 Service Switches 124 Signaling Systems 213 Sockets, Construction of 205 Sockets, Installation of 163 Soldering Fluid Formula 95 Spark Arresters, Construction of 209 Spark Arresters, When Required 113-168 Square Mil 40 Starting Boxes 67-71 Stations, Central 47 Static Electricity, Overcoming 50 Storage Battery Rooms 76 Switch Boards 53 Switches Construction of 188 Switches Electro-Magnetic 114 Switches Installation of 105-124 Switches To Be Double Pole 105 Switches When May Be Single Pole 65-126 Systems, Constant Current 108 Systems. Constant Potential Systems, Extra High, Constant Potential 172 Systems, High, Constant Potential 170 Systems, Low, Constant Potential 114 Tables 229 to 243 Tablet Boards 201 Telegraph, Telephone and Other Signal Circuits. . . . 213 Telephones 23 Testing 59-162-217 Three Wire System 33-117-121-131-218 Transformers in Central Stations 77 Transformers, Construction of 212 Transformers, Inside 171 Transformers, Outside 86 Transmission, Electric 36 Transmission Lines, Over 5,000 Volts 83 Tricks of Trade 224 Trolley Circuits, Grounded 170 Tubes, Insulating 97-185 Volt 11 Watt 15 Wire, Concentric Wire. Conduit Wire, Fixture 17 ,9 Wire, Insulation of J^g Wire, Netting Required on Arc Lamps lld-lOe Wire, Rubber Covered 173 IV INDEX Wire, Slow Burning 176 Wire, Slow Burning, Weather 1'roof 1 T:. Wire, Weather Proof 177 Wires, Car Work 169 Wires, Carrying Capacity, Table 226 Wiring Tables 227 Wires, Central Stations 52 Wires, Concealed Knob and Tube Work 141 Wires, Conduit Work 141 Wires, Number in Conduit 222 Wires, Distance Between Inside 111-136-137-141 Wires. Distance Between Outside 78 Wires, Dynamo Rooms 52 Wires, Extra High Potential 17D Wires, Fished 133-142 Wires, Fixture Work 146 Wires, Low Potential. General Rules 131 Wires, Ground Return 83 Wires, High Potential 170 Wires, Inside, Constant Current 108 Wires, Inside, General Rules !>2 Wires. Underground 104 Wires. Moulding Work IBS Wires, Open Work, Damp Places 137-104 Wires, Open Work. Dry Places 135 Wires, Outside, Overhead 78-S3 Wires, Service 78 Wires. Signal 21 3 Wires, Trolley 82 Wiring Systems 117 THE MOST IMPORTANT BOOK ON ELECTRICAL CONSTRUCTION WORK FOR ELECTRICAL WORKERS EVER PUBLISHED NEW 1904 EDITION. MODERN WIRING DIAGRAMS AND DESCRIPTIONS A Hand Book of practical diagrams and information for Electrical Workers. Sy HENRY C. HORSTMANN and VICTOR II. TOUSLEY Expert Electricians. This grand little volume noc -only tells you how to do it, but it shows you. The book contains no pictures of bells, batteries or other fittings ; you can see those anywhere. It contains no Fire Underwriters' rules; you can get those free anywhere. It contains no elementary considera- tions; you are supposed to know what an ampere, a volt or a "short circuit" is. And it contains no historical matter. All of these have been omitted to make room for "diagrams and de- scriptions" of just such a character as workers need. We claim to give all that ordinary electrical workers neec 1 and nothing that they do not need. It shows you how to wire for call and alarm bells. For burglar and ttre alarm. How to run bells from dynamo current, How to install and manage batteries. How to test batteries. How to test circuits. How to wire for annunciators; for telegraph and gas lighting. It tells how to locate "trouble" and "ring out" circuits. It tells about meters and transformers. It contains 30 diagrams of electric lighting circuits alone. It explains dynamos and motors; alternating and direct current. It gives ten diagrams of ground detectors alone. It gives "Compensator" and storage battery installation. It gives simple and explicit explanation of the "Wheatstoue" Bridge and its uses as well as volt-meter and other testing. It gives a new and simple wiring table covering all voltages and all losses or distances. 16mo., 160 pages, 200 illustrations; full leather binding, I .O\J Sold by booksellers generally or sent postpaid to any address upon receipt of price. FREDERICK J. DRAKE & COMPANY PUBLISHERS aii-213 East Madison Street CHICAGO, U.S.A. DYNAMO TENDING for ENGINEERS Or, ELECTRICITY FOR STEAM ENGINEERS By HENRY C. HORSTMANN and VICTOR H. TOUSLEY, Authors of "Modern Wiring Diagrams and Descriptions for Electrical Workers." This excellent treatise is written by engineers for engineers, and is a clear and comprehensive treatise on the prin- ciples, construction and operation of Dynamos, Motors, Lamps, Storage Bat- teries, Indicators and Measuring Instru- ments, as well as full explanations of the principles governing the generation of alternating currents and a descrip- tion of alternating current Instruments and machinery. There are perhaps but few engineers who have not in the course of their labors come in contact with the electrical apparatus such as pertains to light and power distribution and generation. At the present rate of increase in the use of Electricity it is but a question of time when every steam installation will have in connecton with it an electrical generator, even in such buildings where light and power are supplied by some central station. It is essential that the man in charge of Engines, Boilers. Elevators, etc., be familiar with electrical matters, and it cannot well be other than an advantage to him and his employers. It Is with a view to assisting engineers and others to obtain such knowledge as will enable them to intelligently manage such electrical apparatus as will ordinarily come under their control that this book has been written. The authors have had the co-operation of the best authorities, each in his chosen field, and the information given is just such as a steam engineer should know, To further this information, and to more carefully explain the text, nearly 100 illustrations are used, which, with perhaps a very few excep- tions, have been especially made for this book. There are many tables covering all sorts of electrical matters, so that immediate reference can be made without resorting to figuring. It covers the subject thoroughly, but so simply that any one can understand it fully. Any one making a pretense to electrical engineering needs this book. Nothing keeps a man down like the lack of training; nothing lifts him up as quickly or as surely as a thorough, practical knowledge of the work he has to do. This book was written for the man without an opportunity. No matter what he is, or what work he has to do, it gives mm just such information and training as are required to attain success. It teaches just what the steam engineer should know in his engine room about electricity, r.'ini) Cloth, 1OO Illustrations. Make Them By L. P. DICKINSON This is the very latest and most valuable work on Electricity for the amateur or practical Electrician pub- lished. It gives in a simple and easily understood language every thing you should know about Gal- vanometers, Batteries, Magnets, In- duction, Coils, Motors, Voltmeters, Dynamos, Storage Batteries, Simple and Practical Telephones, Telegraph Instruments, Rheostat, Condensers, Electrophorous, Resistance, Electro Plating, Electric Toy Making, etc. The book is an elementary hand book of lessons, experiments and inventions. It is a hand book for beginners, though it includes, as well, examples for the advanced students. The author stands second to none in the scientific world, and this exhaustive work will be found an invaluable assistant to either the student or mechanic. Illustrated with hundreds of fine drawings; printed on a superior quality of paper. J2mo Cloth. Price, $J.25. Sent postpaid to any address upon receipt of price. FR.EDER.ICK J. DRAKE <& CO. PUBLISHERS 3 J 3 * Chicago A BOOK EVERY ENGINEER AND ELECTRICIAN SHOULD HAVE IN HIS POCKET. A COMPLETE ELECTRICAL REFERENCE LIBRARY IN ITSELF NEW EDITION Handy Vest-Pocket ELECTRICAL DICTIONARY BY WM. L. WEBER, M.E. ILLUSTRATED /CONTAINS upwards of 4,800 words, t; terms and phrases employed in the electrical profession, with their definitions given in the most concise, lucid and comprehensive manner. The practical business advantage and the educational benefit derived from the ability to at ouce understand the meaning of some term involving the description, action or functions of a machine or apparatus, or the physi- cal nature and cause of certain phe- nomena, cannot be overestimated, and will not be, by the thoughtful assidu- ous and ambitious electrician, because he knows that a thorough understand- ing, on the spot, and in the presence of any phenomena, effected by the aid of his little vest-pocket book of refer- ence, is far more valuable and lasting in its impression upon the mind, than any memorandum which he might make a* the time, with a view to the future consultation of some volumin- ous standard textbook, and which is more frequently neglected or forgotten than done. The book is of convenient size for carrying in the vest pocket, being only 2% inches by 5Y t inches, and K inch thick; 224 pages, illustrated, and bound in two different styles: New Edition. Cloth, Red Edges, Indexed . . 25c New Edition. Full Leather, Gold Edges, Indexed, 50c Sold by booksellers generally or sent postpaid to any address upon receipt FREDERICK J. 1)RAKE & COMPANY Publishers of Self-Educational Books for Mechanics 311-213 E. MADISON ST. CHICAGO, U.S.A BOOKKEEPING SELF-TAUGHT By PHILLIP C. GOODWIN : FEW, if any of of the technical works J which purport to be self-instructing? have justified the claims made for* them, and invariably the student either becomes discouraged and abandons his purpose and aim, or he is compelled to enlist the offices of a professional teacher,* which in the great majority of instances is' impracticable when considered in relation to the demands upon time and the condi- tion of life to which the great busy public i subjected. Mr. Goodwin's treatise on Bookkeeping is an entirely new departure from all former methods of self-instruction and one which can be studied systematically and alone by the student with quick and permanent results, or taken up in leisure moments with an absolute certainty of ac- quiring t he-science in a very short time and with little effort. The book is both a marvel of skill and simplicity. Every featuif and every detail leading to the " p.axof scientific perfection are so thor- oughly complete in this logical procedure thorough anvl delily made that the self-teaching and the analysis so thorough anu deUly ro student is led by almost imperceptible, but sure and certain steps to the basic principles of the science, whicn the author in a most compre- yle Tne wprK is tne most masterly ex Bookkeeping and their practical appli English language, and it should be ia every clerk, farmer, teacher and I hensive and lucid style lays bare to intelligence of, even the most mediocre order. The work is the most masterly exposition of the scientific principles of jlication which has ever appeared in the i the hands of every school boy or girl, business or professional man; fora knowledge Of Bookkeeping, even though it may not be followed as a pro- fession, is a necessity felt by every person in business life and a recognized prime factor of business success. , In addition to a very simple yet elaborate explanation in detail of tne eystems of both single and double entry Bookkeeping, beginning with the initial transactions and leading the student along to the culminating exhibit of the balance sheet, the work contains a glossary of all the commercial terms employed in the business world, together with accounts in illustra-j ton, exercises for practice and one set of books completely written up, I2mo Cloth. Price $1.00. Sent postpaid to any address upon receipt of price. Frederick J. Drake & Co., Publishers 2 1 2(3 EAST MADISON ST., CHICAGO NOTICE To the many workmen who are purchasing the publications under the authorship of Fred T. Hodgson, and who we feel sure have been benefited by his excellent treatises on many Carpentry and Building subjects, we desire to inform them that the following list of books have been published since 1903, thereby making them strictly up-to-date in every detail. All of the newer books bearing the imprint of Frederick J. Drake & Co. are modern in every respect and of a purely self-educational character, expressly issued for Home Study. PRACTICAL USES OF THE STEEL SQUARE, two volumes, over 500 pages, including 100 perspective views and floor plans of medium- priced houses. Cloth, two volumes, price $2.00. Half leather, price $3.00. MODERN CARPENTRY AND JOINERY, 300 pages, including 50 house plans, perspective views and floor plans of medium and low-cost houses. Cloth, price $1.00. Half leather, price $1.50. BUILDERS' ARCHITECTURAL DRAWING SELF-TAUGHT, over 350 pages, including 50 house plans. Cloth, price $2.00. Half leather, price $3.00. MODERN ESTIMATOR AND CONTRACTORS' GUIDE, for pricing build- ers' work, 350 pages, including 50 house plans. Cloth, price $1.50. Half leather, price $2.00. MODERN LOW-COST AMERICAN HOMES, over 200 pages. Cloth, pria $1.00. Half leather, price $1.50. PRACTICAL UP-TO-DATE HARDWOOD FINISHER, over 300 pages. Cloth, price $1.00. Half Leather, price $1.50. COMMON SENSE STAIR BUILDING AND HANDRAILING, over 250 pages, including perspective views and floor plans of 50 medium-priced houses. Cloth, price $1.00. Half leather, price $1.50. STONEMASONS' AND BRICKLAYERS' GUIDE, over 200 pages. Cloth, price 91. 50. Half leather, price $2 . 00. PRACTICAL WOOD CARVING, over 200 pages. Cloth, price $1.50. Half leather, price $2.00. Sold by booksellers generally, or sent, all charges paid, upon receipt of price, to any address in the world. FREDERICK J. DRAKE & CO. Publishers 211-213 E. Madison St., Chicago, U. S. A. UNIVERSITY OF CALIFORNIA AT LOS ANGELES THE UNIVERSITY LIBRARY This book is DUE on the last date stamped below* r H 9901 Horstmann - H78m Modern elec