TK N2. JC-NRLF SB Sfl? 53b o o h4 H HH CO tt L-J The PRACTICAL OPERATION of ARC LAMPS NATIONAL CARBON COMPANY CLEVELAND, OHIO 1911 1 Copyright, 1911 by National Carbon Company PREFACE /TTHERE is no more reliable piece of electrical apparatus ^ than the arc lamp. With proper care, suitable car- bons, and a uniform supply of power, it can be depended upon to meet its requirements, but any apparatus exposed to such hard usage as the arc lamp will sooner or later develop deficiencies which, if not promptly rectified, may lead to serious complications. It is with the idea of giving a few suggestions, of laying down a few rules, which, if followed, will increase the efficiency and raise the standard of arc lighting systems, that this book has been prepared. The suggestions offered are necessarily of a very general nature, since they refer to lamps of no particular manufacture and are equally applicable to all types. The authors have been associated with the Engineering Department of the National Carbon Company for a great many years, and their close contact with all types of arc lamps, all brands of carbons, and all arc systems, should, perhaps, enable them to take a more comprehensive view of common arc lamp practice than Engineers who are more directly interested in the develop- ment of some particular type. They will be pleased to take up individually any problem of daily practice which may not be covered by the suggestions outlined in this book. NATIONAL CARBON COMPANY PUBLICITY DIVISION 1911 215437 Enclosed Arc Lamps Enclosed arc lamps may be divided injbo three, general types, the multiple or constant potential^ i'he gesies or constant current, and the series multiple or power cjxcuit lamps. Each of these types is designed to meet cei'tain service conditions. All three types are made fxjx ^ithe/ direct or alternating current. D. C. lamps are preiWable, due to their higher light efficiency and longer lifa^ but the A. C. lamps are very often more desirable becpuse of the more efficient transformation and transmission ol electrical energy possible in A. C. systems. MULTIPLE ARC LAMPS. Multiple lamps are in very extensive use at present and are especially popular for indoor lighting on account of the low voltage required. They may be connected directly across 110 and sometimes on 220 volt circuits. Figure 1 shows the connections for a D. C. multiple lamp. There is only one set of magnet coils, R and S, and these are con- nected in series with each other and in series with the arc. These coils pull directly on the armature P, which operates the clutch C controlling the upper carbon. The operation of the lamp is as follows: When the current is first switched on, the carbons are touching each other and a strong cur- rent flows through the magnet coils. This attracts the armature P, raising the upper carbon and forming the arc. The current decreases as the carbons are separated until, when the arc is the proper length, the .magnets are not strong enough to raise the upper car- bon further. As the carbons are burned away the magnets are weakened and the clutch 5 rod slowly descends until the clutch strikes the stop and allows the\ caVb^Xo. to slip downward. The resistance B, at the top of t t<he lamp, is used to cut down the line vol- tage to i th&t 'required for the arc. The 110 to 125 volt D. 0. lamp operates best with an arc voltage of about 80. Thic resistance is made of German-silver wire wound on a porcelain spool. To regulate it, the clip F is slipped up and down along the guide rod. In addition to cutting dov r ii the line voltage to that required for the arc this resistance serves to steady the light so that small changes v dii' the length of the arc will not cause such great varia- tions. It also prevents the lamp from being short cir- cuited when the carbons are in contact. Although not shown in the figure, a dash pot should be provided to deaden the movement of the regulating mechanism, which results in a steadier arc and more constant illumination. The magnet coils are sometimes provided with taps on each coil to adjust the lamp to burn at different current strengths. The lamp shown in the figure has three taps, 1-2-3, in each coil. In another form of lamp the current strength is adjusted by means of small weights placed on top of the upper carbon holder. The switch on the top of the lamp is used to open the circuit when any repairs or adjustments are being made. The upper car- bon holder slides within a tube and connection is usually made to it by a flexible cable. In the lamp shown in Fig. 1 this tube has a slot in its side and through it an extension of the carbon holder projects. To this the flexible cable is connected. In another form the flexible cable is run directly from one of the binding posts of the lamp into the top of the tube and no slot is required. A third lamp has no tube but is supplied with two guide rods on which the carbon holder slides. The carbon holder consists of a three-jaw spring clutch which grips the end of the carbon. Many forms of clutches are used. They are usually made wholly of metal, though a metal ring lined with a porcelain bushing is sometimes used. One of the most common forms of clutch consists of two clamping rings around the carbon, the lower ring being supported by the upper. Another form consists of a metal sleeve with a clamping lever at one side. For 220-250 volt D. C. cir- cuits two types of lamps are available. One, with a single pair of carbons burns with an arc voltage of 140-150. The second, called a Twin Carbon lamp, uses two pairs of elec- trodes placed side by side and connected in series as shown in Fig. 2. Both pairs of car- bons are controlled by the same regulating mechanism. The best results will be obtained if the lamp is adjusted for 80 volts at each arc. A. C. lamps may be operated on circuits of any fre- quency from 25 to 140 cycles. The standard for lighting is 60 cycles, and lamps operating on this frequency give better service than on the lower values wjiere flickering is liable to occur. With frequency much above 70 cycles the operation of the lamp is liable to become noisy. The A. C. multiple lamp, shown in Fig. 3, operates on exactly the same principle as the D. C. There are some points about its construction, however, that are radically different. For a regulating resistance, a choke coil instead of a German-silver wire resistance is used. This cuts down the line voltage just as a resistance would, but does not consume nearly as much power. It consists of a number of coils of copper wire wound on an iron core and connected in series with each other. By varying the number of coils connected in series with the arc, the arc voltage may be varied. Referring to Fig. 3, all the coils except AB give an adjustment of 3 to 4 volts. This is a half coil and gives a change of 2 volts, so by always keeping one lead on tap A or B close adjustment can be obtained. By means of this choke coil lamps may be adjusted to operate on different frequencies as well as for dif- ferent values of line voltage on the same frequency. Other adjustment in the lamp mechanism will usually have to be made for changes in the frequency or current. This type of lamp is used on 110-120 volt circuits only and burns with an arc voltage of 72. All the magnet cores of the lamp are made of laminated iron, i. e., of thin sheets of iron riveted together. The constant reversal of the direction of the magnetism when AC is used would induce currents in solid cores which would weaken the magnetic effect and also cause heating. In the D. C. lamp these parts are made solid. For 220 and 440 volt A. C. cir- cuits, self-contained lamps using an auto transformer instead of a choke coil can be obtained. The auto transformer consists of a number of small separate coils mounted on a ring shaped core of laminated iron. The voltage adjustment is made by means of taps from one of the transformer coils to which a flexible lead is connected. Tf sufficient change in voltage 8 cannot be obtained in this way, the terminals of the lamp may be shifted to another coil. The connections of this lamp are shown in Pig* 4. SERIES ARC LAMPS. Series arc lamps are used chiefly for street or other outdoor lighting and for industrial plants. As many as 100 enclosed arc lamps are connected in series on one circuit. This would give a voltage of 100x75=7500 across the terminals of the circuit assuming a lamp voltage of 75. The line current is held at a con- stant value by apparatus in the power house or sub- station (see page 35). Since the current is the same, no matter what the length of the arc, it is evident that a series coil alone cannot regulate this lamp. Fig. 5 shows the connections, for an A. 0. series lamp. Owing to the difficulty of generating D. C. at the high voltage required, comparatively few D. C. series lamps are being installed. The two magnets, A and B, operate the pivoted lever F, to which the clutch rod is connected. The coil A is connected in series with the arc, while B is connected in shunt across the arc. The series coil tends to separate the carbons and the shunt coil to allow them to come together. The resistance H, called the starting resistance, is connected across the terminals of the lamp through the cut-out K, which is operated from the lever F. When the current is turned on the carbons are in contact and part of the current flows through the series coil and the rest through the starting resistance. The series magnet pulls up its end of the lever separating the carbons and opening the cut- out K. As the carbons are separated the voltage across the arc rises and strengthens the shunt coil until when the proper length of the arc is reached it equalizes the series magnet. As the carbons are consumed the shunt magnet becomes stronger than the series and lowers the carbon. If the carbon fails to feed and the arc becomes too long, the shunt magnet will pull up its end of the lever until it closes the cut-out K. The switch S is used for short-circuiting the lamp while making repairs. To adjust this lamp to operate with different values of line current, the **, weight M on the pivoted lever is slipped along its guides. In some lamps this adjustment is made by a resistance shunted across the series coil, as shown in Fig. 6. In this lamp both coils have a shunt and a series winding. The dash pot D is used to steady the movement of the clutch lever. The carbon holder and clutch are like those used in the multiple lamp. The series lamps need no adjusting resistance in series with the arc. SERIES MULTIPLE ARC LAMPS. Series multiple, or power circuit lamps, are usually operated two in series on 220 volt circuits, or five in series on 500 volt circuits. They are used extensively on D. C. motor circuits, especially for lighting shops or parks on electric railway lines where only the 500 volt power from the trolley is available. One form of this type is very similar to the series, except that they are supplied with a compensating resistance equivalent to that of the arc. When a lamp goes out for any reason this compensating resistance is switched in so that the other lamps in series with it will not be affected. This resistance is connected in series with a cut-out controlled by the shunt coil in exactly the same way as the starting resistance in the series lamp. The lamp is also supplied with a regulating resistance in series with the arc. Each lamp of the set is adjusted to consume its proper proportion of the voltage. For example, with two lamps in series on a 220 volt circuit with an arc voltage of 80, each lamp should consume 110 volts, so the regulating resistance should be adjusted for 30 volts. Another form of series multiple lamp is the same as the multiple, except that it has a small equalizing weight attached to the clutch mechanism, in such a way as to neutralize any tendency which one lamp in the series may have to take more than its share of voltage. MINIATURE AND INTENSIFIED ARC LAMPS. In the last few years many types of arc lamps burning small carbons (about ^4-inch in diameter) have been put on the market. These lamps are the result of the demand for a high efficiency lighting unit, and are intended primarily for interior lighting. They are all multiple lamps and most of them are made for D. C. circuits only, but there are several A. C. lamps of this type. The regulating mechanism of most of these lamps resembles that of the multiple lamps already described. One lamp of this type, however, is radically different. Three car- bons are used. The two upper carbons are of small size inclined towards each other and touching at their lower ends. The arc is thus maintained without the aid of any regulating mechanism. The lower carbon is of larger size and is fed upward by means of a series coil, main- taining the arc in a fixed position. The two upper car- bons are burned alternately. The lamps of this type are called Miniature, Small Arcs and Semi-Enclosed by differ- ent manufacturers. They owe their high efficiency primarily to the small diameter of the carbons used. This causes a relatively high current density and a high 11 degree of incandescence at the tip of the carbon. Heat is not as readily carried away by the small carbons as by the larger ones of the enclosed arc. The arc is steadier and does not wander over the end of the carbons as in enclosed lamps. Cored carbons are used. The light obtained from these lamps is pure white and is one of the best known substitutes for daylight. The bluish tinge noticeable in the enclosed lamp is entirely absent. This makes the lamps particularly well suited for lighting stores and other places where color matching is important. The manufacturers have spent much time in designing the case and globe equipment and supply their lamps in most attractive forms which would add to the decora- tion in any building. A special feature of one of these lamps is that it is provided with a terminal so that it may be screwed into an incandescent lamp socket. These lamps may be procured for 110 volt D. C. and A. C. and for 220 volt D. C. circuits. GLOBE AND REFLECTOR EQUIPMENT. This will naturally be governed by general conditions. The stand- ard equipment consists of a light opal inner and clear outer globe. The advantage of the light opal inner globe is that the opal globe becomes luminous and forms a secondary source of diffused light which eliminates shadows, and at the same time gives a more effective light due to the better distribution. For interior work, there is the further advantage that the violet rays are partly absorbed, thus making a whiter light. Two clear globes should not be used except for photo- graphic work where a light is required which is high in actinic value. Special conditions sometimes call for other combinations, such as clear inner and opal outer, etc. In a number of cases no outer globe is needed. For A. C. lamps a reflector is usually used, either with or without an outer globe. A considerable portion of the light from an A. C. arc is thrown upward, and if no reflector were used, this light would be lost. 12 General Rules for Operation and Care of Enclosed Arc Lamps Only those rules which apply to all types of arc lamps can be given. Further information on any particular type can be obtained from the instruction books of the manu- facturers. CARBONS. In order to obtain satisfactory operation of enclosed arc lamps, only high grade carbons should be used. They should be straight, round and of uniform diameter, being free from blisters and dirty spots. Should these spots be present, they should be removed with sand paper before the carbons are inserted in the lamp. COLUMBIA carbons, manufactured by the National Car- bon Company, Cleveland, Ohio, have given excellent satis- faction in practically all cases where they have been tried. Their manufacture is closely watched and controlled by an elaborate testing system which eliminates the possi- bility of crooked, blistered, or dirty carbons reaching the trimmers 7 hands. The raw materials used are of the highest obtainable purity and are constantly kept at this standard by frequent chemical analyses. Carbons should be stored in a dry place. Do not place boxes of carbons for any length of time on a cement floor having an earth foundation. If they must be stored in such a place, put boards under them so as to allow free circulation of air. Trimmers should use a covered bag to protect the car- bons from dust and dampness. Burned carbons, cleaning cloths, or other material should not be allowed to come in contact with the carbons. For D. C. lamps solid carbons should be used almost invariably, with the exception of the miniature and other small lamps, which use as a rule two cored carbons. Most enclosed arc lamps are designed to burn upper carbons 12 inches long and in practically all cases the stub left over from the upper carbon is used for the lower of the 13 next trim. This should be from 4^ to 6 inches long, as specified by the manufacturer. About 3 to 4 inches of lower carbon is consumed per trim, so it is evident that the number of hours burning per inch of lower carbon is high. To a trimmer cutting off carbons, ^-inch will not appear of much importance, but in a lamp burning 150 hours it will mean a life of about 10 to 12 hours. Some arrangements should be made for cutting off carbons the proper length. This can readily be done at the station. If the lower carbon is too long it is liable to cause break- age of the inner globe or melting of the gas cap. A large percentage of inner globe breakage occurs during the first 15 minutes of burning after retrimming. This is when the lower carbon is at its maximum length, with the arc near the top of the globe, and at the same time the globe is undergoing a large temperature change. On the other hand, if the lower carbon is too short, it will burn down into the carbon holder. In cutting the old upper carbon for the lower of the next trim, the end which has been in the upper holder should be cut off and the carbon placed in the lamp with the burned end to the arc. This brings the lamp to full candle power in a minimum length of time and sometimes prevents flaming and possible globe breakage. In the D. C. lamp the upper carbon should always be positive, since it is consumed more rapidly. If the lower carbon were positive, it would be consumed in a short time, the carbon holder would be destroyed and the globe melted. With the positive carbon at the bottom, most of the light is thrown upward and not downward. To test for the polarity of a lamp, allow it to burn for a few minutes, then turn it off. The hotter carbon, i. e., the one remaining red longer, is the positive. For A. C. lamps one cored and one solid carbon are used, but on circuits where the voltage and frequency vary considerably, two cored carbons will often give better results. The lower carbon should be from 5% to 7 inches long. In this type of lamp both carbons are consumed at about the same rate. The A. C. lamp, as a rule, uses a Q 1 /^ or 12 inch upper carbon. In trimming an arc lamp the upper carbon should be pushed up as far as it will go in order to make good contact with the holder. Carbons with slightly beveled ends will facilitate this operation. The carbon should slide through the clutch and the bushing of the gas cap freely. After trimming, the clutch should be able to separate the carbons, about 1 inch in the case of the multiple lamps and ^ inch in the series. If the carbons cannot be separated far enough, it will cause high cur- rent in the multiple lamps, which may blow the fuse or possibly burn out a coil, while the series lamps will operate with a short arc which will cause globe blacken- ing. To test a lamp after trimming lift the clutch by pushing on the rod leading to the magnets. Lifting the carbons is only half a test. GLOBES. The inner globe should be thoroughly cleaned at every trimming. Most of the large operators of arc lamps are doing this work at a central globe cleaning plant. Duplicate sets of inner globes and, with lamps with detachable holders, of lower holders are provided. All globes are washed at the station. Soap is not required and, if it is used, the globes should be thoroughly rinsed in clean water. The grease from the soap if left in the globe may cause blackening. If the number of globes to be washed each day is large, the work can be facilitated by the use of a revolving brush, running under water, or with a continuous stream of water supplied to it. The lower carbons are cut to size at the station and when- ever possible the lower carbon and inner globe are assembled in the holder. The globes are then packed in partitioned baskets or boxes, which the trimmer carries around in a wagon. In trimming he has simply to sup- ply a new upper carbon and replace the dirty globe with 15 a clean one. If the lower carbon holders are not detach able, the lower carbon and the clean globe must be fitted into the holder at the lamp. Central station globe clean- ing is advisable whenever the size of the installation allows it. When globes are cleaned on the street, two cloths should be used, one wet for washing the globes and the other for drying. The wet cloth should be rinsed fre- quently in clean water. If the deposit sticks to the globe it can be readily removed by a weak solution of muriatic acid. GAS CAPS. Gas caps should be kept clean. Other- wise the deposit from the gas caps will form on the inner globe. Corrosion or dirt on the gas cap always produces short life, since it is impossible to seat the inner globe properly. Gas checks or vents should be kept clean at all times. If possible, blow out this dust. A small pair of bellows may be used to advantage in cleaning gas checks. If an attempt is made to clean the vents with a stick, the deposit is more likely to be packed into the vent than to be removed from it. In lamps with removable gas caps, it is well to replace the caps at regular intervals of a month or more and return the used caps to the station for a thorough clean- ing. With this type of gas cap, trouble has resulted due to the supporting hook being bent or becoming loose. This forces the cap out of place, causing the carbons to bind. This same trouble is caused by the lower lamp frame springing. Considerable trouble is encountered due to warped or cracked gas caps. CAEBON LIFE. In order to obtain long life, it is necessary that the inner globe should be air tight. Open base globes as a rule will give longer life than closed base by about 20 to 25 hours. This is due to the fact that the open base globe is smaller, and therefore con- ic tains less air, initially. The tendency for leakage in the two types is about the same, for while the open base globe has two openings, the closed base has a larger leakage surface at the top. When using open base globes care should be taken to set the globe properly to exclude the air. The globe rests on an asbestos washer in the lower carbon holder. An old, hard washer keeps out the air better than a new one, so it should be renewed only when worn out or torn. If the edge of the globe is kept free from chips, a washer should last for years. When replacing washers, the old one should be removed and the holder cleaned before a new washer is inserted. In setting globes supported by a bail, turn the globe until it will not rock. If such a position cannot be found, the seat of the gas cap must be cleaned and trued up before normal carbon life can be obtained. A nicked or cracked globe will reduce the carbon life materially. Leaks at the bottom may be easily tested for by blowing into the top of the globe. Leaks at the top of the globe are not so injurious as those at the bottom, but will materially reduce the life of the carbon. They may be caused by any of the following reasons: a chipped globe, small carbons, worn gas cap bushing, gas caps not setting squarely against the globe, or warped gas caps. The gas cap bushings should be renewed as soon as they begin to show signs of wear. Other causes which may produce short carbon life are: (a) loose dash pots, causing the lamp to jump; (b) high arc voltage or any condition that produces flaming; (c) excessive fluctuations in voltage or current; (d) plugged gas check, causing direct ventilation; (e) frequent starting and stopping of lamps; (f) excessive humiditV; (g) the lamp subjected to strong draught. Globes have been founq in which the ground edge were \ 17 not perpendicular to the. axis of the globe. This may cause the carbons to bind in the gas cap. The effect of rapid burning is to produce points on the carbons like those obtained in the open arc lamp. The globe and its handling has more effect on the life of the trim than any other factor. For this reason the life of a brand of carbons should not be judged by less than ten complete burn-out tests. POOR LIGHT. When a lamp is furnishing poor light the trouble may lie in any of the following points: (a) fresh trim; (b) low voltage or current; (c) lamp not lined up, causing carbons to burn with heavy diagonal faces and cast heavy shadow to one side; (d) dirty globe. Low voltage may be caused by: (a) low line voltage this will affect all the lamps on the circuit; (b) improper adjustment of lamp mechanism for operat- ing conditions; (c) carbon, dash pot or clutch binding; (d) failure of clutch ring or tongue to grip carbon; (e) excessive vibration of lamp, causing carbons to slip through holder. GEAPHITIZATION. Graphitization is caused by low line voltage. Graphitized points occur in any interme- diate stage between soft, greasy graphite and hard, lava- like beads. When graphitization occurs with cored car- bons, the cores are stopped up and the lamp will operate as if two solid carbons were being used, i. e., it will jump badly. If these points are broken off, the lamp will operate properly until new points are formed. This trouble is very apt to occur in the D. C. lamp if the arc voltage falls below 75 and in the A. C. if below 70. With low arc voltage the clutch operates badly and allows the carbon to slip, causing poor burning and excessive globe 18 deposit. Small or flat carbons will cause graphitization with normal arc voltage. Graphitization never occurs in lamps operated on normal voltage with carbons of the correct size. JUMPING-. Carbons should always be kept dry. Damp carbons cause the lamp to jump badly when the current is first turned on. In damp, cored carbons steam will be formed, which is liable to blow out the coring material and give the same effect as an A. C. lamp operating with solid carbons. Oil and grease on the carbons cause the lamp to jump badly and will also cause globe blackening. Most manu- facturers of arc lamps direct that no oil should be used on their lamps and certainly it should not be used where there is any danger of its getting on the carbons. At the present time most lamps use graphite dash pot plungers and these require no lubrication. If the dash pot plunger is too loose the lamp will jump badly when it is first turned on, but it will soon become quiet. If it is too tight, the lamp starts quietly, but the arc voltage will vary considerably and the arc will break more or less frequently. Intermittent jumping may be caused by a poor -contact in the lamp circuit. To locate this examine the lamp parts, fuses, switches, etc., for signs of heating or arcing. A. C. lamps will jump badly if two solid carbons are used. FLAMING. Flaming is usually caused by the presence of air in the inner globe. It is, therefore, likely to occur when a lamp is first started. In A. C. lamps it may be lessened by digging out the core of the new cored carbon for about % inch. High arc voltage will cause flaming. This large power consumption at the arc\ will cause excessive heat, which will blacken and sometimes even melt the globe. The product of the arc combustion is a white powder, iron sul- phate, which is deposited on the gag cap and top of the 19 globe. The intense heat of the arc when it is flaming converts this white powder to a brown or red substance and will finally burn it into the glass. This seriously inter- feres with the light of the arc. SLIPPING. Worn clutches will cause the carbons to slip badly. In such cases new clutches should be supplied. BUENED OUT SHUNT COILS. Burned out shunt coils are a frequent cause of trouble in series arc lamps. If the carbons stick and the cut-out fails to work, the current through the shunt coil becomes excessive and a burn-out is sure to result. The mechanism may wedge and hold the contact open after the arc has broken and the same thing will occur. The cut-out contacts should be kept in good condition and, if burned or oxidized, should be cleaned with sand paper. If there is improper adjustment, it may cause the lamp to burn with an abnormally long arc. This causes high current in the shunt coil, but usually not sufficient to cause a burn-out. In the multiple arc lamp, improper adjustment may cause overheating and possible burning out of the series coils. If the carbons wedge together in the multiple lamp, the current drawn from the line will be excessive and the regulating resistance will be burned out if the fuse does not blow. This high current may damage the insulation of the series coil. LAMP ADJUSTMENT. If an individual lamp gives short life for several trimmings, it is probable that it is out of adjustment and is operating at a high arc voltage. An examination of the carbons will usually tell if this is the case, high arc voltage producing pointed carbons. The lamp should be readjusted to operate at the correct arc voltage and current. For this work an ammeter and a voltmeter are necessary. It is advisable to test and to properly adjust all lamps for actual working conditions before they are connected on the line. All lamps are thoroughly tested by the manu- facturer before they are shipped, but the conditions under 20 factory test and actual operating conditions may be decidedly different. A careful inspection should also be made before the lamps are placed in service, and afterwards at regular intervals to see that no screws are loose and that all parts are in good condition. There is a continual tendency, especially in the A. C. lamp, for the connections to become loose, causing arcing and throwing the lamp out of adjust- ment. OPERATING TROUBLES. A lamp may fail to start for the following reasons: (a) open circuit, external or internal; (b) grounded circuit; (c) dash pot stuck; (d) carbon bound in trolley tube, clutch or gas cap; (e) joints of clutch fail to work. When trouble occurs with a lamp, the most effective method is to replace it and send the defective lamp to the shop where it should be thoroughly inspected and repaired. A small number of extra lamps should always be kept in stock to replace the lamps under repairs. A lamp should never be kept in service when it is not operating properly, for in a short time it will be ruined and in the meanwhile will give unsatisfactory service. Eeeords of operation and repairs should always be kept on suitable blanks to be filled out by trimmers. Such a system can be kept with little expense and the actual operating conditions noted. A Few Pointers Trim lamps regularly and carefully. See that lamps are adjusted for the proper voltage and current. Keep globes and gas caps clean. Use high grade glassware. Use COLUMBIA carbons. 21 Flame Arc Lamps When flame arc lamps were introduced into this country several years ago, they were considered useful only for spectacular advertising, but they soon proved themselves to be practical units for lighting large areas, such as streets, parks, or industrial plants, their immense candle power and high efficiency allowing a much higher standard of illumination than could be obtained by any other means. A flame arc lamp consuming 550 watts will pro- duce between five and six times as much light as the ordinary enclosed arc consuming 660 watts. The orange yellow color of the light has been found to be extremely well suited for lighting shops and railways yards where a large amount of smoke is liable to be present in the air. Flame lamps may be divided into two general classes, the inclined carbon lamp in which both carbons are mounted side by side inclined toward each other at an angle of about 30 and the vertical carbon lamp in which one carbon is superimposed above the other as in the ordinary enclosed arc. The first is probably the most popular type. INCLINED CARBON LAMPS. In these lamps there are three distinctly different regulating mechanisms used, clock feed, motor feed and gravity feed. In the clock feed lamp the carbon holders are suspended by chains or flexible wires wound on a drum. The downward move- ment of the carbons is controlled by a ratchet operated by shunt and series coils. This mechanism was formerly used on D. C. lamps only, but recently several manu- facturers have applied it to their A. C. lamps. The motor feed is used on A. C. lamps only. The carbons are sus- pended just as in the clock feed lamps. The drum instead of being controlled by a ratchet has an aluminum disc attached to it, which rotates between the poles of shunt H D- K and series magnets. The gravity feed lamp does not employ any electrical method of control for feeding the carbons. The carbon holders are rigidly connected . together and one of the carbons is supported at its lower end on a projection of the economizer or some device attached to it. The carbons are fed downward as they are consumed. To steady the arc and hold it in a bowed position at the ends of the carbons, a magnetic blow down coil connected in series with the arc is used in most inclined carbon lamps. All inclined carbon lamps use an arch-shaped porcelain plate called an economizer. The carbons pass through holes in the top and the arc is situated directly under the bowl: The economizer partly encloses the arc and reduces the con- sumption of the carbons. It soon becomes covered with a white ash deposit and serves as an excellent reflector. It also protects the arc from draughts and thus greatly improves the burning qualities. A clock feed lamp with its casing removed is shown in Fig. 7. H is the series and K the shunt coil operating the armature E, which controls the drum supporting the carbons. Eaising the armature releases the ratchet and allows the carbons to feed downward. When the lamp is first turned on, the carbons are separated and no current can flow through the series coil. The shunt coil, Fi S- however, is excited and pulls up the armature, allowing the carbons to feed downward. At the same time, a shoe, situated on the top of the economizer and operated from the armature E by a rod at the back of the lamp, pushes f ^ ~*J over the right hand carbon until it touches the left, clos- ing the circuit through the lamp. Current then passes through the series coil pulling down the armature. This stops the feed and removes the shoe, allowing the right carbon to fall back to its position to form the arc. As the carbons are consumed, the strength of the shunt coil increases and the carbons are fed downward. This increases the strength of the series coil which stops the feeding. The dash pot D is used to steady the movement of the armature. R is the regulating resistance to cut down the line voltage to that of the arc. B is the blow down coil in series with the arc. Fig. 8 shows another clock feed lamp of different con- struction. The carbon holders C and C' are rigidly connected together and supported on the vertical rod B. This rod has a spiral groove cut into its side Fig. 8. and as this rod turns the car- bons are fed downward. The rod is controlled by the series coil H and a shunt coil K at the back of the lamp. R is the regulating resistance and D the dash pot. Fig. 9 shows the mechanism of a motor feed lamp. The aluminum disc D is connected to the shaft of the drum on which the chains supporting the carbon holders C and C' are wound. This disc rotates between the poles of the series magnet H and the shunt magnet K. The current induced in the disc by the series mag- n e t rotates the drum in the direction to raise the car- b o n s, while that induced by the shunt tends to rotate it in the other direction low- ering them. When the lamp is turned on the shunt mag- net is excited and the car- bons are lower- ed until they touch. Current then fl o w s through the Fig. 9. Fig. 10. series coil which raises the carbons forming the arc. As the carbons are separated the strength of the series coil decreases, while that of the shunt increases until when they are of the same strength the disc is held in equilibrium. As the carbons are consumed the arc volt- age increases and the shunt coil becomes the stronger and lowers the carbons. R is the regulating resistance and B the blow down coil. This type of lamp uses no dash pot, the magnetic forces on the disc acting as dampers. The mechanism of a gravity feed lamp is shown in Fig. 10. The carbons are supported by a projection on the economizer and are fed downward as the carbon resting on the support is burned away. The carbons are held apart by the series coil operating the rod and, as soon as the current ceases to flow through this coil, the unsupported carbon falls into contact with the other. The carbon holders are rigidly connected together and slide on the center vertical rod. When the lamp is switched on, the carbons are in contact and the current flowing through the series coil separates the carbons and forms the arc. This lamp burns one round carbon. The other has a rib, which rests on the support. Many attempts have been made to increase the burn- ing period of flame lamps by the use of more than one pair of carbons. These are usually called magazine lamps. One type uses two pair of carbons, the second pair being switched into the circuit after the first is consumed. In another type the carbons are burned alternately, the arc changing from one pair to another every few minutes. As many as eight or ten pairs of carbons are used in some lamps. The carbons are usually held in a vertical rack or magazine. One of the recent forms of magazine lamps uses two pairs of flat carbons with bridged cores, as shown in Pig. 11. The two carbons of the same polarity are inclined toward each other I and touch at their lower ends, thus supporting them- selves, and feeding down- ward by gravity as they are I consumed. While the lamp is in service the positive and negative electrodes are held apart by magnet coils at the top of the lamp. When these coils are not energized all four carbons are in contact. The arc wanders across the ends of the carbons consum- ing them evenly. This lamp may be procured to give burning periods up to 100 hours. VERTICAL CARBON LAMPS, in a way, are nothing but modifications of the open and enclosed arcs burning flaming carbons. In most cases the regulating mechanism is very similar to that of the multiple enclosed arc lamp already described. In most cases no economizer is used, but one of the well known types uses an economizer with a focusing arc, i. e., both carbons are fed, the upper one downward and the lower one upward, in this way keep- ing the arc directly below the bowl of the economizer. This lamp uses a clock-work feed. Another form, called the regenerative fl a m e arc lamp, is an enclosed lamp with suitable condensing tubes at the sides to col- lect the mineral fumes from the arc and prevent their deposit on the inner globe. The arc chambers and condensing tubes are shown in Fig. 12. The heat of the arc causes a circu^ lation of the gases through the tubes as indicated by the arrows. Condensation takes place on the cooler walls of the tubes. The inner globes and tubes are prac- tically air-tight, so a long burning period of from 60 to 70 hours is obtained. This lamp uses a star- shaped lower carbon, open- ings between the ribs being filled with flaming material. 12. The upper carbon is round, with six small cores contain- ing flaming material. In the D. 0. lamp the lower carbon should be positive. The distribution of the light given by the inclined car- bon and the vertical trim lamps is shown in Fig. 13 by the curves A and B. The inclined carbon gives its maxi- mum intensity directly downward, as shown by A, so that to properly illuminate a large area, it is necessary that the lamps be hung high. One company manufacturing inclined carbon lamps uses an inner prismatic globe to improve the distribution, as shown in curve C. The vertical carbon lamp gives a distribution with its maxi- mum intensity 15 20 below the horizontal (curve B). This kind of a distribution curve is more suitable for street lighting than the other because it throws out more of its light toward the point of minimum illumination, i. e., half way between the lamps, consequently the difference between maximum and minimum illumination will not be so great. Operation and Care of Flame Arc Lamps Flame arc lamps are made for operation on both direct and alternating current circuits. They are usually con- nected two in series across 110 or four in series across 220 volt circuits. However, there are lamps on the market which may be connected three in series across 110 volt circuits and others which may be placed directly across 110 volts. A. C. lamps are sometimes operated from constant potential circuits of 110 to 550 volts through a compensator or transformer hung directly above the lamp. In most cases the lamps connected in series multiple are not provided with a compensating resistance, so if one lamp goes out, the others in series with it go out also. A. C. flame lamps may be operated on circuits of any frequency from 25 to 140 cycles. ARC VOLTAGE. The arc voltage of most of the inclined carbon lamps varies between 42 and 48. If it falls below 40 the lamp is liable to flicker, or rises over 50 the carbons will be consumed too rapidly and the lamp does not burn steadily. The arc voltage of the vertical carbon lamp varies widely with the form of lamp. One type uses arc voltage of 38-42, while the regen- erative type burns with 68-72 volts across the arc. It is most important that a lamp should burn with the correct value of arc voltage as specified by the manufacturer. A high arc voltage will cause rapid consumption of the carbons and consequent decrease in burning period. A low arc voltage will cause a weak light. CARBONS. Only the very highest grade of carbons should be used. They should be straight, have a smooth surface, and be of uniform diameter and composition. SILVEETIP CARBONS, manufactured exclusively by the National Carbon Company, satisfy all the demands of the flame lamp. They are made of the highest grade of materials and are accurately gauged, both for size and 29 straightness. In addition, they have that important mechanical feature the Silver Tip which does away with the loose end of wire found in other flame carbons. This makes trimming easy and always insures a good contact between the carbon and holder. Another impor- tant advantage of the SILVERTIP is that there is no necessity of throwing away any carbons because of broken wires. The, carbons should be kept dry; damp carbons cause the lamp to flicker badly and the steam formed when the lamp is turned on is liable to blow out the cores. When trimming a flame arc lamp with carbons contain- ing metallic cores, care should be taken that the wires in the carbons are placed on the side away from the ajc, otherwise the arc will operate badly and cause flickering. When the carbon holders are rigidly connected, as in the gravity feed and some clock feed lamps, it is extreme- ly important that the carbons should be exactly the same length. Otherwise, the longer carbon must be cut off before inserting it into the lamp. In most cases the A. G. lamp uses carbons of the same size, but the D. C. takes a slightly larger positive than negative. D. C. lamps must always be connected to the line with the polarity correct, otherwise they will burn with a weak white light and the carbons will be consumed unevenly. Any lamps connected in series will also be affected and burn unsteadily. The polarity can be found by allowing the lamp to burn a few minutes and then turning it off, the hotter carbon is the positive. The positive carbon has a larger incandescent area. The terminals of most D. C. lamps are marked P or N for positive or negative. In the vertical carbon lamps the positive carbon should be the lower, which is the reverse of enclosed arc practice. Most inclined carbon lamps are made in two sizes, the ten-hour lamp burning carbons 400 mm. long and the 30 seventeen-hour lamp burning carbons 600 mm. long. There is a twenty-hour lamp on the market burning carbons 650 mm. long. The color of the light of the flame arc depends on the chemicals with which the carbons are impregnated. The yellow light is usually the most efficient and for that reason is most widely used. The red is next, giving an efficiency of 10 to 20 per cent, lower than that of the yellow, while the white is still lower 25 to 40 per cent, lower than the yellow. STRIKING- POINT. To obtain a long life from flame arc carbons the arc should always burn within the bowl of the economizer. To obtain this the carbons must have the correct striking point. For adjusting this, the lamp manufacturers furnish steel rods with squared ends of the exact size of the carbons. These are placed in the lamp and fed downward until they touch. This position for clock feed lamps should be in line- with the lower edge of the economizer, as shown in Fig. 14. For the motor feed lamps the striking point should be % inches below the lower edge of the economizer, as in Fig. 15. If the rods are not available, carbons whose ends have been squared with a file may be used. When the lamps operate poorly and whenever new lamp parts are supplied, the striking point should be adjusted. BURNED-OUT ECONOMIZERS. If the arc is allowed to burn too near the top of the economizer, or with too high an arc voltage, the economizer is liable to be burned out. This trouble may also occur if both carbons stick and the arc travels up the carbons. 31 SLIPPING. Trouble is sometimes experienced due to carbons slipping. This may be caused by some part of the lamp mechanism sticking or by projections on the carbon. Care should be taken to see that the carbons are smooth before inserting them in the lamp. When one carbon hangs, the other will be fed downward to the end of its travel and if it is long enough to strike the ash pan, it will connect one side of the line to the frame of the lamp. This may develop a short circuit at some weak spot in the lamp. This trouble could only occur in lamps using independent carbon holders. CLEANING. At each retrimming, the globe equipment and all lamp parts on which the products of combustion have condensed should be cleaned thoroughly with a brush or with a dry cloth. The condensing tubes of the regenerative lamp should be cleaned with a brush. The manufacturers give the following rules for cleaning: Insert the brush into the lower opening of the regenera- tive chamber; the brush can then be passed up into both tubes and also through the globe, taking special care to clean deposit from the portion over the globe, and leave the tubes unobstructed. Obstruction in the tubes will prevent the lamp burning. Before inserting the lower cone holder, care should be taken to clean off all traces of white powder from the cone surface, both on the lamp frame and holder. An occasional application of graphite will entirely prevent sticking of the cone in its seating. Deposit in the outer globe is caused by the inner globe cap not seating tightly upon the inner globe. With the regenerative lamp, care should be taken in seating the globes properly as it is necessary to secure air-tight joints in order to obtain a maximum life from the carbons. Heavy globe deposit will cause a decided decrease in the light. Flickering may be caused by wet or greasy carbons, or by a wet globe. 32 Jumping is caused by high arc voltage and by damp or greasy carbons. Intermittent jumping may be caused by a loose connection in the circuit. One of the large manufacturers of flame arc lamps gives the following rules for operation. If lamp fails to operate satisfactorily, open case and carefully inspect the follow- ing parts: Dashpot Must be quite clean and plunger slide easily in same; if it does not, wipe carefully with clean cloth. On no account use ordinary emery paper or oil in the dashpot. Examine the screws holding the dashpot to its seat and see if they are tight and hold the dashpot firmly. Armature See if this works smoothly and freely with- in the solenoid tube throughout its range of motion. If necessary, clean the inside of solenoid tube with a clean cloth. Upper Holder See that the slotted end of the holder grips the carbon firmly. Be sure that the carbon requires a perceptible pull to come out of holder, or it may drop out accidentally and short-circuit the lamp. Use a full length carbon, pushing it upwards to its full movement, and allowing it to fall by its own weight, with; fingers supporting it. This will show that it is free from friction and all danger of binding or sticking when lamp is burn- ing. Clutch See that this rises smoothly on its guide rod. Note that it grips carbon promptly and firmly, and that the carbon when gripped by clutch cannot slip through, even when pulled downwards by hand. Try if the clutch is easily released by the weight of the mechanism; the mechanism when moving as slowly as possible (guide this with a finger) should be able to press the clutch flat on its seat. Chips off upper carbon will sometimes collect under clutch and should be removed. 33 TABLE 1 Light Reflected by Various Colors Per Cent. White blotting paper 82 White cartridge paper 80 Ordinary foolscap 70 Ordinary newspaper 50 to 70 Chrome yellow paper 62 Orange paper 50 Plain boards, clean 45 Plain boards, dirty 20 Yellow wall paper 40 Light pink ! 36 Blue 25 Yellow painted wall, clean 40 Yellow painted wall, dirty 20 Emerald green paper 18 Dark brown 13 Vermilion 12 Blue-green 12 Cobalt blue 12 Black 0.5 Deep chocolate 0.4 French ultramarine 3.5 Black cloth 1.2 Black velvet 0.4 Table shows how important it is to have light colored walls and ceilings. TABLE 2 Interior Illumination The desirable intensity of illumination for various classes of interior service has been given as follows: Auditoriums 1 to 3 ft. candles Theatres 1 to 3ft. Churches 3 to 4 ft. Beading 1 to 3 ft. Eesidences (General) 1 to 2 ft. Desks , 2 to 5 ft. Bookkeeping 3 to 5 ft. Postal service 2 to 5 ft. Stores (General) 2 to 5 ft. Stores (Clothing) 4 to 7ft. Drafting .5 to 10 ft. Engraving 5 to 10 ft. 34 fl.C SUPPLY IA/VWWWV\! Station Equipment Multiple arc lamps require no special equipment, but are connected directly across incandescent lighting or power circuits. The series lamps, however, require special apparatus to hold the line current at a constant value at all times, no matter how many lamps are cut out of the circuit. Series lamps may be operated on either D. C. or A. C., but at the present time very few D. C. series carbon lamps are being installed. CONSTANT CURRENT APPARATUS. Constant cur- rent D. C. may be supplied by a special arc dynamo, or from a mercury arc rectifier. These dynamos are series wound and, in most cases, use a solenoid regulator connected in series with the line for controlling the current. In one type of machine the brushes are shifted on the commutator, increasing or decreasing the line voltage as may be necessary. In another, a resist- ance is shunted across the field winding. By varying this resistance the strength of the field and con- sequently the voltage of the machine is varied. The armatures are some- times made with several independent windings for supplying separate lamp circuits. The voltage that can be obtained from each of these cir- cuits is 3000 to 5000 and usually about 50 enclosed lamps are connected in series on a single circuit. A mercury arc rectifier is sometimes used to obtain con- stant current. It is connected on the secondary winding 35 of a constant current transformer, which will be described later. The transformer supplies constant current A. C. to the rectifier, which delivers constant current D. C. to the line. These elementary con- nections are shown in Fig. 16. For obtaining constant cur- rent A. C. a special trans- former, or a choke coil regu- lator, is used. The operation of the transformer depends on the fact that the current induced in a secondary coil by a primary varies inversely as the distance between the two coils; that is, as this distance increases, the current induced decreases. A constant current transformer is shown in Fig. 17. It consists of a laminated iron core C around which the stationary coil A is placed. Above A suspended from the pivoted lever I) is the movable coil B. The weight of the coil is counterbalanced by the adjustable weight G. The currents in the primary and secondary coils cause them to repel each other so that by properly adjusting the weight G the secondary may be regulated to give the desired current. When the current exceeds this value the coils will be separated further, reducing the current to its proper value. The movable coil is usually the second- ary and the stationary the primary. These transformers are made in sizes up to 100 lamps on a single circuit. On the larger sizes, one type has two primary and two secondary coils, the primaries usually being fixed at the top and bottom, while the secondaries move between them. In this case the counterbalance mentioned above is con- 36 VVWVWVV 1 fi^.18. VWWWV\/V J siderably smaller. In the first case the counterbalance is equal to the weight of the moving coil less the electrical repulsion, while in the second case the two moving coils are balanced against each other, and the counter-weight simply balances the repulsive force. Therefore, in adjusting ^ p] these transformers the current is Q increased by decreasing the counter-weight in the small sizes, and by increasing it in the larger sizes. In another type a single primary coil is placed in the center of the core with a secondary coil suspended on each side. A separate weight is used to counterbalance each secondary coil. Most constant current trans- formers are air-cooled, and a dash pot is supplied to prevent the moving coil from see-sawing every time a variation in cur- rent occurs. If this oscillation were not checked, the lamps on the circuit would flicker. Some transformers are oil-cooled, and in these the dash pot is not necessary as the resistance which the oil offers to the motion of the coil is sufficient to prevent flickering. A simple wiring diagram for a constant current trans- former and the necessary instruments is shown in Fig. 18. When switching on a lamp circuit using a constant cur- rent transformer, the movable coil should be raised to its highest position before the switch is closed to avoid the heavy flow of current caused by the carbons of all the lamps being in contact. Where there are two mov- able coils, these should be in the central position when 37 starting, that is as far away from the stationary coils as possible. Instead of a transformer a single coil regulator or choke coil is sometimes used. When an alternating current passes through a coil of wire, it reacts on itself and a counter e. m. f. is induced, which opposes the flow of the current. This counter e. m. f. is greatly increased by inserting an iron core in the coil. One type regulator operates on this principle. It con- sists of a movable coil A (Fig. 19) connected in series with the lamps. It is sus- pended and counterbalanced just as the movable coil in the transformer. When the cur- rent rises above the desired value, it strengthens the mag- netic effect of the coil and pulls it up further into the core. This increases the chok- ing effect of the coil and the current is reduced. A dash pot is usually provided to steady the movement of the coil. This dash pot is objec- tionable for small variations, but is desirable when a large movement of the coil is necessary, as when several lamps cut out at the same time. This difficulty is overcome in one type of regulator by supplying a dash pot with a certain amount of lost motion. In another type of regulator the coil and core are both movable, and suspended in such a way as to counterbalance each other. The elementary wiring diagram for a regulator is shown in Fig. 20. A step-up transformer is used between the supply circuit and the lamps. This is not necessary 38 when the supply circuit is of the proper voltage, but it is always advisable to use the transformer no matter what the supply voltage may be as it separates the arc lamp circuits from the supply mains. This trans- former should preferably be supplied with taps to give various voltages, so that the number of lamps installed may be changed at any time without decreas- ing the efficiency of the system. When starting an arc lamp circuit using a regu- lator, care should be taken that the regulator is in the "no load" position before the switch is closed. In some regulators a latch is provided to hold the coil in this position. After the current is turned on, the latch should be loosened and the regulator slowly moved to the run- ning position. In another regulator, a reactance coil is connected directly across the lamp circuit through the lower terminals of the starting switch. When the cur- rent is turned on, the line is short-circuited through this reactance coil and the regulator moves to its no-load position. The starting switch should now be closed. This short-circuits the reactance coil and opens the circuit across the line. The switchboards used for series arc lamp circuits are of a distinct type. It is sometimes advisable, in cases where a number of arc lamp circuits are used, to be able to connect a transformer on any one of several circuits and to have several transformers available for each cir- cuit. This is accomplished by using two sets of bus bars. The transformers are connected to a vertical set, while the lamp circuits go to the horizontal. Plug switches are provided where the bars cross to connect any transformer to any lamp circuit. The wiring for a switchboard for three lamp circuits is shown in Fig. 21. The black circles k show where the plug switches are inserted, while the light ones indicate the position of the other switches. The vertical bars at the right of the diagram are not con- nected to any transformer, but are used for inter- connecting circuits in various ways. For instance, in the diagram as shown, circuits 1 and 2 are both connected in series to transformer 1, while circuit 3 is connected to transformer 3. It is advisable, but not necessary, to use a current transformer for the ammeter in the lamp circuit. It should always be done in circuits of over 35 lamps. It is customary to use a voltmeter and wattmeter in the primary circuit of the transformer. All outgoing lines should be protected with lightning arresters, Line Work For outside series arc lamp circuits weatherproof wire should be used. The line should be designed not only for carrying capacity, but should have sunicient tensile strength to withstand a high wind when the wire is covered with ice. The voltage of the circuit is high, so care should be taken to insulate it properly and allow sufficient clearances. Outside lamps may be suspended in three ways: 1, placed on the top of the pole; 2, suspended from brackets at the side of the pole or building; 3, suspended on a wire stretched across the street. The first method does not allow the lamp to be lowered and steps must be pro- vided to allow the trimmer to climb the pole. The second and third methods are practically the same, in one case the lamp is suspended from an arm on the pole and in the other from a steel cable. In both cases the lamp is arranged to be lowered to the street. A y 2 inch or % inch hemp or cotton rope is used to raise and lower the lamp. A flexible wire or chain may be used, but it should always contain a strain insulator for the trimmer's protection. Enough rope may be provided to allow the lamp to be lowered, or it may be cut short and have a loop in the end, in which case the trimmer carries a short rope which he hooks to the end of the lamp rope when the lamp is being lowered. The pulley should be provided with a clutch which will support the lamp in case the rope breaks or becomes untied. Pulleys with hoods to protect them from snow and sleet should be used. A short cross-arm insulator should be fastened directly above the lamp to which the wires are connected. Each multiple lamp should be provided with a suitable 41 fuse to protect it from being burned out and to protect the other lamps on this line from disturbances due to a single lamp. The height a lamp should be hung above the street depends on local conditions. In open streets where there are no trees to interfere lamps may be hung fairly high 25 to 30 feet. In shaded streets this should be less. For inside work the wire for series arc lamp circuits should have approved rubber covered insulation. The wires should be arranged to enter and leave the building through an approved double contact service switch mounted in a non-combustible case free from moisture and easily accessible in case of fire or other emergency. By a double contact switch is meant one which first short-circuits the loop and then disconnects it from the main circuit. The wires should be in plain sight and never encased except when required by the inspection department. The insulators supporting the wires should separate them at least 1 inch from the surface wired over. The wires should be held rigidly at least 8 inches from each other. Lamps should be hung from insulated supports other than their conductors. 42 Locating Troubles on Series Arc Lamp Circuits The three chief causes of trouble which may occur on series arc lamp circuits are breaks, grounds and crosses. When the whole wire is broken the trouble can easily be detected, but it frequently happens that the conductor breaks and the insulation supports the wire, giving no visible indication of trouble. This is liable to occur where the wire is dead ended to the insulator at the lamp. Grounds are of two kinds. The dead ground in which the circuit has permanent connection to the earth; and the arcing ground, such as is caused by the wet branch of a tree being blown against the wire where the insula- tion is poor. This gives an intermittent ground, which is liable to burn the wire. Crosses occur when the two sides of the line come into contact with each other, short- circuiting part of the lamps. This trouble should not occur on a well constructed line. In testing for grounds and open circuits an ordinary magneto is about the best thing to use. A portable Wheat- stone bridge is also very useful and a high reading volt- meter can often be used to good advantage. Arc lamp circuits should be tested during the day while the power is off for grounds and open circuits. To test for grounds connect one terminal of the magneto to the line and the other to a water pipe or some other good ground. If the line is all right the bell should not ring. To test for an open circuit connect the magneto across the line. If the circuit is closed the bell will ring. An open circuit may be located as follows: A lamp circuit supposed to be open at O is shown in Fig. 22. A and B represent the terminals of the circuit at the 43 station between which the first test indicating that the line was open was made. These two points are then con- n e c t e d together and grounded. j c The tester goes to ,vj /*** about the center U j / I (2) B'/ \ of the line or j^ I @- @ @ @ I some other con- venient point where he disconnects both wires from a lamp and tests the two halves of the circuit for grounds, i. e., connects one terminal of the magneto to the line and grounds the other. The half of the circuit which is closed will show up the ground at A, but the other half will give no indication. By proceeding along the grounded part of the circuit and repeating this test at intervals the broken place can be located between narrow limits, after which the break can usually be found by inspection. Grounds may be located in very much the same way as shown in Fig. 23, where the line is supposed to be grounded at G. In this case the terminals of the cir- cuit A and B are not grounded but left open. The tester goes to some point C where he disconnects a lamp and tests both sides for grounds. The side 011 which the ground exists will show up. By proceeding as before the position of the ground may be located. Locating grounds with a Whcatstone bridge obviates the tester's having to go out on the line. Suppose the circuit shown in Fig. 23 was ground- A ed at G. With the bridge measure the resistance between, the terminal A of the line and the ground; call it Ea. Also measure between B and the ground, calling it Eb. Then the distances from the sta- tion to the point G along the two lines are proportional to these resistances. A G : EG :: R a : Eb A simple modification of the "Wheatstone bridge method is to use a high reading voltmeter while the lamps are burning. Readings are taken between each side of the line and the ground and these are proportional to the distances along each side of the line to the ground. Care of Electrical Measuring Instruments Electrical measuring instruments should be handled carefully and not subjected to any jars or hammering. Portable instruments are often placed in positions where they are subjected to a strong magnetic field or to high temperatures. Both of these cause errors in the reading. In the permanent magnet type of direct current instru- ments if the temperature is increased the strength of the magnets will be decreased which tends to decrease the reading of the instruments, but at the same time the strength of the holding spring will be decreased and these two errors tend to neutralize each other. As a general rule, however, these meters will read low when they are hot. In the ammeters of this type with an internal shunt the heat from the shunt will usually cause the instru- ment to read low. Up to about 25 amperes these meters read correctly, but above that they should not be left in the circuit at all times. Direct current meters for read- ing large currents should be provided with an outside shunt. Errors will be caused by stray magnetic fields, the size depending upon the strength of the field. An alternating current field if weak will not affect a direct current meter, but if strong it will exert a de-magnetizing effect upon the meter and cause a low reading. These fields may be caused by any electric generator or motor, a conductor carrying current, or by other meters. Switchboard meters should be shielded from the effect of these fields by an iron case. Other causes of errors which may be mentioned are the friction of pivots, defective springs and lack of balance of moving parts. These faults, however, should not be found in well made meters. 46 For measuring A. C., current transformers and not shunts should be used. Care should be taken that no more meters are connected on the secondary of the trans- former than the number which it is designed to carry. At light loads the ratio of transformation is not accurate and small errors will be introduced. The secondary of both current and potential instrument trans- formers on high potential lines should be grounded. This not only protects the operator but prevents errors due to static electricity. In the A. C. induction meters the error due to small changes in frequency should be slight. Eattling and humming of meters is caused by loose parts. In the D. C. wattmeters the case may become per- manently magnetized and affect the reading. Wattmeters should be inspected at least once a year when they should be thoroughly cleaned and the pivot at the bottom oiled. The creeping of wattmeters is usually due to vibration of the wall on which they are fastened. The potential coil is connected to the line at all times and this in connection with the starting coil gives a small torque. Another cause is the connection of a meter on a higher voltage than that for which it is adjusted. A good wattmeter should give accurate read- ings on both light and heavy loads under a wide variation of power factor, frequency and wave form. The damping magnets should not lose their magnetism and the case should be moisture, bug and dust proof. Good electrical contact is extremely important with all measuring instruments. This is particularly important in the low reading milli-voltmeters when used for measur- ing current with external shunt. If the resistance of the meter is only a few ohms, a corroded or dirty terminal may introduce a large percentage of error. 47 Inside Wiring The Rules of the National Board of Fire Underwriters published in the National Electric Code for the installa- tion of light and power apparatus should be followed in all cases where no municipal ordinances are in effect. The following are some of the requirements: In all electric work conductors, however well insulated, should always be treated as if they were bare. To the end that under no condition, existing or likely to exist, can a short circuit occur and that all leakage from con- ductor to conductor, or between conductor and the ground, may be reduced to a minimum. In all wiring special attention must be paid to the mechanical execution of the work. In laying out an installation, except for constant current systems, every reasonable effort should be made to secure distribution centers located in easily accessible places, at which points the cut-outs and switches controlling several branch cir- cuits can be grouped for convenience and safety of opera- tion. The load should be divided as evenly as possible among all the branches and all complicated and unneces- sary wiring avoided. Wires must not be smaller than No. 14 B. & S. gauge, except for fixtures and flexible cords where No. 18 may be used. Tie wires must have an insulation equal to that of the conductors which they confine. Wires 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 con- ductors. Stranded wires must be soldered before being fastened under clamps or binding screws, and whether stranded or 48 solid, when they have a conductivity greater than that of No. 8 B. & S. gauge, they must be soldered into lugs for all terminal connections. The wires must be separated from contact with walls, floors, timbers or partitions through which they pass, by non-combustible, non-absorptive, insulating tubes, such as glass or porcelain, except at outlets where conduit is used. Wire should run over, rather than under, pipe upon which moisture is likely to gather. Where underground service enters a building through tubes, the tubes shall be tightly closed at the outlet by asphaltum or other non-conductor to prevent gases from entering the building through such channels. Overhead wires entering the basement of a house should do so through a conduit passing through the wall. When entering above ground, the wires should pass through insulating tubes slanting upward. Automatic cut-outs must be placed on all service wires, either overhead or underground, as near as possible to the point where they enter the building and arranged to cut off the entire circuit from the house. Cut-outs must be placed at every point where a change is made in the size of wire, unless the cut-out in the larger wire will protect the smaller. No set of incandescent lamps requiring more than 660 watts, whether grouped on one fixture or several, should be dependent upon one cut-out. Special permission may be obtained of the Inspection Department for departure from this rule in the case of large chandeliers. The rated capacity of fuses must not exceed the allow- able carrying capacity of the wire as given in Table No. 3. Circuit breakers must not be set more than 30% above the allowable carrying capacity of the wire unless a fusible cut-out is also installed in the 'Circuit. Switches 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. When possible, switches should be so wired that blades will be "dead" when the switches are open. They should not be placed so that they tend to fall closed. The ground wire in the D. C. three-wire system must not be smaller than No. 6 B. & S. gauge. In A. C. systems it must never be less than No. 6 B. & S. gauge and must always have a carrying capacity equal to that of the secondary lead of the transformer, or the combined leads where transformers are connected in parallel. On three-phase systems the ground wire must have a carry- ing capacity equal to any one of the three mains. FOR OPEN WORK. For open work approved rubber or "slow-burning weatherproof " insulated wire should be used. The rubber covered wire is used in cellars and in other places subjected to moisture or acid fumes. The wires 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: Vnltnp-P Distance from Distance between surface. wires. to 300 y 2 inch 2y 2 inches 301 to 550 1 inch 4 inches Where wiring runs along flat surfaces, supports at least every 4y 2 feet are required. If the wires are liable to be disturbed, the distance between the supports should be shortened. Wires should not be " dead-ended " at rosettes, but should be carried beyond them for a few inches and securely fastened with porcelain cleats. FOR MOULDING WORK. Moulding work should never be used 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 50 brick walls as they are likely to sweat and thus introduce moisture into the moulding. Approved rubber insulated wire should be used. CONCEALED KNOB AND TUBE WORK. This is allowed by the underwriters rules but prohibited by ordinances in a great many cities. Approved rubber covered wire should be used. The wire must be separated at least 1 inch from the surface wired over and must be kept at least 10 inches apart, and, when possible, should be run singly on separate timbers or studdings. They must be separated from contact with walls, floors, timbers, etc., through which they pass by insulating tubes, such as glass or porcelain. Eigid supports are required under ordinary conditions at least every 4^ feet, but a generous use of tubes, cleats, or knobs is advisable in places where the circuits are entirely concealed and where any derangement can not be observed. All outlets must be protected by insulating tubing or by conduit. In cases of combination fixtures the tubes must extend at least flush with the outer end of the gas cap. CONDUIT WIRING. Conduit wiring is the best and safest, and the only kind allowed in fireproof buildings. Iron pipes with galvanized or enameled interiors are most exclusively used. The smallest size conduit has an interior diameter of % inch. Care should be taken that the insides of the pipes are free from rough spots or projections. The entire system of conduit must be con- tinuous, and permanently and effectively grounded. The inside edge of bends should never have a radius of less than 3% inches, nor more than the equivalent of four quarter bends should be placed between two outlets. Eubber covered wire should be used. In A. 0. circuits it is necessary and in D. C. it is advisable that the two sides of the circuit should be contained in the same conduit. Calculation of Size of Wire The size of an electrical conductor is usually given in circular mils. A mil is one thousandth of an inch, and a circular mil is the area of a circle, the diameter of which is one mil. To obtain the area of a conductor in circular mils, knowing the diameter, all that is necessary is to multiply the diameter expressed in mils by itself, i. e., square the diameter. For example a ^-inch cable has a diameter of 250 mils and an area 250 X 250 62,500 circular mils. Every conductor offers some resistance to the flow of current. This resistance increases as the length increases and decreases as the cross section increases. For metal conductors this resistance increases as the temperature rises. The resistance of one foot of copper wire with a cross section area of one circular mil has been found to be 10.8 ohms at 75 F. For wiring calculations this is commonly taken; as 11. ohms. The resistance of any conductor is, therefore _ 11 X L ~K~ L = Length of the conductor in feet. A = cross section area in circular mils. For example 1,000 feet of %-inch cable with an area of 62,500 circular mils has a resistance of 11 X 1000 The voltage (E) consumed when current flows through a conductor is equal to the product of the current in amperes (I) and the resistance in ohms (R). E = IXR If the cable referred to above were carrying 100 amperes, the volts drop in the cable would be E = 100X0.176 = 17.6 volts. 52 From the two equations already given a third can be obtained by substituting the value of (R) from the first into the second _IX11 XL E ~ A" 11 XL XI A = E This equation is used for finding the size of wire (A) in circular mils necessary to carry a known current over a given distance with a certain allowable drop in voltage. For example: What size of wire will be necessary to carry 100 amperes over a distance of 300 feet with volt- age drop of 5? To carry the circuit over a distance of 300 feet will require 600 feet of wire. A = 11X6 ; OX10 =132,000 circular mils. t). Looking up in the table the nearest size is No. 00. The current values given in the table must not be exceeded and in cases where the allowable drop is large the values given in the table and not the drop will determine the size of the wire to be used. To calculate the drop it is necessary to know the cur- rent flowing in the circuit. In incandescent lamp circuits this depends on the efficiency of the lamps and on the voltage and may be calculated approximately from the following formula: __ N-Z-P ~E~ I = Current in amperes. N = Number lamps connected in parallel in the circuit. P = Candle power of lamps. Z = Watts consumed per c. p. in the lamps. E = Voltage of the circuit. The following values of Z will give fairly good results. 3.5 for 110 volt carbon filament incandescent lamps. 4.0 for 220 volt carbon filament incandescent lamps. Tungsten and Tantalum lamps are rated in watts, in which case this value is substituted for P Z, the formula becoming N X W ~!T W = watts consumed in one lamp. In most cases the distance to be used in calculating the size of wire should be an average, for example with a circuit 200 feet long with lamps distributed over the last 100 feet, the distance taken should be 100 + y 2 (100) -150 feet of circuit. The allowable drop is usually given in per cent, of the voltage. To obtain the actual volts drop, multiply the voltage by the per cent, drop, pointing off two places, i. e., a 2% drop on a 100 volt line would be 100 X .02 = 2 volts. What size of wire is necessary for a 110 volt incan- descent lighting circuit 400 feet long carrying 40 16 c. p. carbon filament lamps. The lamps are distributed over the last 50 feet and a 2% voltage drop is allowed. The distance to the center of distribution is: 350 + % X 50 = 375 feet. Therefore 375 X 2 = 750 feet of wire should be used in the calculations. 40 X 16 X 3.5 The current I = j^TT ~ 20<4 am P- The allowable drop D = 110 X .02 = 2.2 volts. 11 X 750 X 20.4 A= =76500 circular mils. 4.4 The nearest size to this is No. 1 B. & S. gauge. The carrying capacity is sufficient for the current. 54 TABLE 3 Carrying Capacity of Copper Wires The following table, showing the allowable carrying capacity of copper wires and cables of 98/ conductivity, 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 84% of that given in the following tables for copper wire with the same kind of insulation. B. & S. Gauge Circular Mils. Table A. Rubber Insulation. Amperes. Table B. Other Insulations. Amperes. 18 1,624 3 5 16 2,583 6 8 14 4,107 12 16 12 6,530 17 23 10 10,380 24 32 8 16,510 33 46 6 26,250 46 65 5 33,100 54 77 4 41,740 65 92 3 52,630 76 110 2 66,370 90 131 1 83,690 107 156 105,500 127 185 00 133,100 150 220 000 167,800 177 262 0000 211,600 210 312 Circular Mils. 200,000 200 300 300,000 270 400 400,000 330 500 500,000 390 590 600,000 450 680 700,000 500 760 800,000 550 840 900,000 600 920 1,000,000 650 1,000 1,100,000 690 1,080 1,200,000 730 1,150 1,300,000 770 1,220 1,400,000 810 1,290 1,500,000 850 1,360 1,600,000 890 1,430 1,700,000 930 1,490 1,800,000 970 1,550 1,900,000 1,010 1,610 2,000,000 1,050 1.670 The lower limit is 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. 65 TABLE 4 Properties of Copper Wire English system Brown & Sharpe gauge. Numbers . Diameters in mils. Areas in circular mils. C. M.=d 2 . Weights 10GJ ft. Pounds. Resistance per 1000 ft. in International ohms. At 75 F. 0000 460. 211 600. 641. .049 66 000 410. 168 100. 509. .062 51 00 365. 133 225. 403. .078 87 325. 105 625. 320. .099 48 1 289. 83 521. 253. .125 8 2 258. 66 564. 202. .157 9 3 229. 52441. 159. .200 4 4 204. 41 616. 126. .252 5 5 182. 33 124. 100. .317 2 6 162. 26 244. 79. .400 4 7 144. 20 736. 63. .506 7 8 128. 16 384 50. .641 3 9 114. 12 996. 39. .808 5 10 102. 10 404. 32. 1.01 11 91. 8 281. 25. 1.269 12 81. 6 561 20. 1.601 13 72. 5 184. 15.7 2.027 14 64. 4 096. 12.4 2.565 15 57. 3 249. 9.8 3.234 16 51. 2 601. 7.9 4.04 17 45. 2 025. 6.1 5.189 18 40. 1 600. 4.8 6.567 19 36. 1 296. 3.9 8.108 20 32. 1 024. 3.1 10.26 21 28.5 812.3 2.5 12.94 22 25.3 640.1 1.9 16.41 23 22.6 510.8 1.5 20.57 24 20.1 404. 1.2 26.01 25 17.9 320.4 .97 32.79 26 15.9 252.8 .77 41.56 27 14.2 201.6 .61 52.11 28 12.6 158.8 .48 66.18 29 11.3 127.7 .39 82.29 30 10. 100. .3 105.1 31 8.9 79.2 .24 132.7 32 8. 64. .19 164.2 33 7.1 50.4 .15 208.4 34 6.3 39.7 .12 264.7 35 5.6 31.4 .095 335.1 36 5. 23. .076 420.3 56 I ^. ^-OT- it^eoiOt-- '-I -l C<J CO Tt< O 00 gle Ph - r4 ^H C^ cvj 10 CO 00 C< T OiOCOi-Ht^ O IO l>- -J^ Force, Work and Power A force may be defined as an action which changes or tends to change the relative position of a body. It is usually expressed in pounds. Work is the exertion of a force through space. Work must always be accompanied by motion, and is measured by the product of the force and the distance through which it acts. Work = Force X Distance. The unit of work usually employed is the foot-pound, i. e., the work done when a force of one pound is exerted through a distance of one foot. Power is the rate of doing work. The unit, the horse- power,* is the amount of power required to lift 550 Ibs. at a uniform velocity of one foot per second. 1 H. P. = 550 ft. Ibs. per sec. = 33,000 ft. Ibs. per min. = 1,980,000 ft. Ibs. per hr. *United States standard. 58 Electrical Energy The power that is transmitted by any electric circuit depends on the current and the voltage. The unit, the watt, is the amount of power obtained from one ampere at one volt. This unit is too small for ordinary purposes and the kilowatt equal to 1000 watts is used. For D. C. circuits W = C X E. W = Power in watts. C Current in amperes. E = Electromotive force in volts. In A. C. circuits the entire current is not always avail- able for doing work. This calls for another term in the energy equation, the power factor, which is the ratio of the current available for power to the total current. For single-phase A. C. circuits the equation becomes W = G X E X P. P = Power factor of the circuit. For two-phase A. C. W = 2XCXEXP. For three-phase A. C. W = 1.73XCXEXP. Electrical and Mechanical Conversion Factors 1 H.P.= 746 watts = .746 kw. 1 kw. = 1.344 H.P. = approx. 1J^ H.P. 59 Measurement of Heat The British Thermal Unit (B. T. U.) is the unit usually employed in heat measurements. It is that quantity of heat required to raise one pound of pure water 1 F. at or near 39.1 F. This unit varies slightly as the density of the water changes, but for ordinary calnihit ions it is assumed to be constant. The Metric unit is the Calorie or quantity of heat required to raise one kilogram of water 1 ( '. at. its maximum density near 4 C. 1 B.T.U. = .252 calories. 1 Calorie = 3.968 B.T.U. The Small Calorie is the quantity of heat required to raise one gram of water 1 C. at or near 4 C. 1 Calorie = 1000 Small Calories. Mechanical Equivalent of Heat The Mechanical Equivalent of Heat is the number of units of mechanical energy equivalent to a unit of heat energy. This value has been found to be 1 B.T.U. = 778 ft. Ibs. 1 H.P. hr. = 2,545 B.T.U. 1 K.W. hr. = 3,412 B.T.U. The Thermal Capacity of a body is the amount of heat required to raise it one degree. The ratio between this amount and that required to raise an equal weight of water at its maximum density one degree is the Specific Heat of the substance. 60 Calculation of Temperature by the Rise in Resistance The resistance of metal conductors increases as the temperature rises. The change in resistance per ohm per degree rise in temperature is called the temperature co-efficient. If E is the resistance of a conductor at C and a, the temperature co-efficient for that conductor, then its resistance at tC is Rt=R (1 + at ) When the resistance of a conductor at tiC is known and the resistance at I^C is desired, the equation becomes R2=Ri (i + Itl) The A. I. E. E. temperature co-efficient for commercial copper wire is 0.0042 per C. Using this value the equa- tion for copper conductors becomes (1-f .0042 t 2 ) ?* *i (i + .0042 tj The most common application of the resistance formula is to calculate the temperature of a conductor knowing its resistance also the resistance and temperature of the conductor when cold. Solving for t 2 the equation becomes For copper conductors with a = 0.0042 t 2 = |* (238 + 0-238 The temperature co-efficient for aluminum is 0.0039 for 1 C. For steel it is 0.005 and brass 0.0038. Horse Power Calculations BOILER PRESSURE rid. 24. ATMOSPHERIC PRESSURE To measure the available horse power supplied to an engine, it is necessary to know the steam pressure on the face of the piston at all times during the forward stroke. Also the steam pressure opposing the piston on the return stroke. These pressures are measured by an instrument called an indicator which is connected on a pipe leading from the cylinder of the engine. This instrument makes a diagram a s shown in Fig. 24, representing the pressure in the cylinder during ZERO PRESSURE 'the complete forward and backward stroke. The average height of this figure represents the effective pressure available for doing work during one revolution of the engine. This is called the Mean Effective Pressure or M.E.P. The value of the horse power obtained by using the mean effective pressure is called the Indicated Horse Power or I.H.P. TTTP -PXLXAXN 33,000 P = Mean effective pressure in pounds. L = Length of the stroke of the engine in feet. A = Area of the piston head in square inches. N = Speed of engine in revolutions per minute. 33,000 = The number of foot-pounds per minute in a horse power. This formula gives the horse power on one end of the cylinder only, i. e., for a single acting engine. 62 The value of the mean effective pressure depends on the maximum steam pressure, the percentage of stroke which has taken place when cut off occurs and on the back pressure, i. e., whether the engine is exhausting into the air or if a condenser is used and if so on the amount of vacuum. The horse power available at the pulley is called the Developed Horse Power or D.H.P. and may be obtained from the following formula: D.H.P. =~ n G X A X N 33,000 ?r= 3.1416 G = Difference in pull on two sides of the belt. A = Eadius of the pulley in feet. N Speed of pulley in revolutions per minute. The mechanical efficiency of the engine is D.H.P. E = I.H.P. Atmospheric Pressure The pressure due to the atmosphere is 14.7 Ibs. per square inch at the sea level. This decreases as the eleva- tion increases until at one mile it is about 12 Ibs. For a rough approximation it may bei assumed that the pressure decreases one-half pound per 1,000 feet of elevation. The pressure 14.7 Ibs. per square inch corresponds to the pressure of a column of mercury 29.92 inches in height, or a column of water 33.9 feet. 63 Weight of Substances (Kent's Mechanical Engineer's Pocket Book.) Weight of Water The weight of a cubic foot of water varies with the temperature. The point of maximum density is 39.1 F. At 32 F freezing point 62.418 Ibs. 39.1 F maximum density 62.425 Ibs. 62 o F 62.355 Ibs. 212 F. boiling point under one atmos. . .59.76 Ibs. The boiling point of water depends on the pressure to which it is subjected rising as the pressure increases. Under a pressure of one atmosphere (14.7 Ibs. per square inch) it boils at 212 F. The specific gravity of a substance is the ratio of its weight to that of an equal volume of water at its maxi- mum density. 64 TABLE 6 Weight and Specific Gravity of Metals (Kent's Mechanical Engineer's Pocket Book.) Specific Gravity Approximate Mean Value used hi Calculation of Weight. Weight per Cubic Foot, Pounds. Aluminum 2 67 167 Antimony. . . 6 76 422 Bismuth 9 82 612 Brass: Copper + Zinc. 80 20 8 60 536 70 30 60 40 8.40 8 38 524 521 50 50 8 20 511 Bronze: Copper, 95 to 80 ( 8 85 552 Tin, 5 to 20 j Gold pure 19 26 1201 Copper . 8 85 552 Indium 22 38 1396 Iron cast . . 7 22 450 1 ' wrought 7 70 480 Lead . ... . . 11 38 710 Manganese 8 499 Magnesium. 1 75 109 ( 323 Mercury . < 60 13.62 13 58 849 847 / 212 Nickel. . . 13.38 8 8 834 549 Platinum 21 5 1347 Silver . 10 51 655 Steel... 7 85 490 Tin. . . 7 35 458 Zinc 7 00 437 65 TABLE 7 Weight and Specific Gravity of Stones, Brick, Cement, Etc. (Kent's Mechanical Engineer's Pocket Book.) Pounds per Cubic Foot. Specific Gravity. Asphaltum 87 1 39 Brick, Common. 112 1 79 " Pressed 135 2 16 " Fire 140 to 150 2 24 to 2 4 Brickwork in mortar. . . . 100 1 6 " cement 112 1 79 Cement, Portland, loose . 92 in barrels 115 Clay 120 to 150 1 92 to 2 4 Concrete 120 to 155 1 92 to 2 48 Earth, loose 72 to 80 1 15 to 1 28 rammed 90 to 110 1 44 to 1 76 Gneiss i 160 to 170 2 56 to 2 72 Granite f Gravel ... 100 to 120 16 to 1 92 Lime, quick, in bulk 50 to 60 .8 to .96 Limestone 140 to 185 2 30 to 2 90 Marble 160 to 180 2 56 to 2 88 Masonry dry rubble 140 to 160 2 24 to 2 56 dressed ... 140 to 180 2 24 to 2 88 Mortar . 90 to 100 1 44 to 1 6 Pitch 72 1 15 Sand . . . 90 to 110 1 44 to 1 76 Sandstone. 140 to 150 2 24 to 2 4 Slate 170 to 180 2.72 to 2.88 Tile. . . 110 to 120 1 76 to 1 92 66 TABLE 8 Metric System Measures of Length 10 millimeters (mm) ... =1 centimeter cm. 10 centimeters =1 decimeter * dm. 10 decimeters =1 meter m. 10 decameters =1 hectometer Hm. 10 hectometers =1 kilometer Km. Measures of Surface (Not Land) 100 square millimeters . . =1 square centimeter . . sq. cm. 100 square centimeters . =1 square decimeter ...sq. dm. 100 square decimeters . . =1 square meter sq. m. Measures of Volume 1000 cubic millimeters . . =1 cubic centimeter . . .cu. cm. 1000 cubic centimeters . =1 cubic decimeter . . . .cu. dm. 1000 cubic decimeters . . =1 cubic meter cu. m. Measures of Capacity 10 milliliters (ml.) =1 centiliter cl. 10 centiliters =1 deciliter dl. 10 deciliters =1 liter 1. 10 liters =1 decaliter Dl. 10 decaliters =1 hectoliter HI. 10 hectoliters =1 kiloliter Kl. Measures of Weight 10 milligrams (mg) =1 centigram eg. 10 centigrams =1 decigram dg. 10 decigrams =1 gram g. 10 grams =1 decagram Dg. 10 decagrams =1 hectogram Hg. 10 hectograms =1 kilogram .Kg. 1000 kilograms =1 ton T. The gram is the weight of 1 cu. cm. of pure distilled water at 39.2 F. TABLE 9 Conversion Factors 1 mm = 0.03937 in. 1 cm = 0.3937 in. 1m = 39.37 in. = 3.281 ft. = 1.094 yds. 1 Km = 1093.6 yds. = .621 miles. 1 in = 25.4 mm = 2.54 cm. 1 ft = 30.5 cm - 0.305 m. 1 yd = 0.914 m. 1 mi = 1609 m = 1.609 km. 1 sq. mm = 0.00155 sq. in. 1 sq. cm 0.155 sq. in. 1 sq. m = 1550 sq. in. = 10.764 sq. ft. = 1.196 sq. yd. 1 hectom = 11959.9 sq. yds. = 2.471 acres. 1 sq. in = 645.2 sq. mm.. . . = 6.452 sq. cm. 1 sq. f t =s 929. sq. cm = 0.093 sq. m. 1 sq. yd = 0.836 sq. in. 1 acre = 4046.87 sq. m = 0.4047 hectare. 1 cu. cm = 0.061 eu. in. = 0.00211 pts. (U.S. liquid) 1 liter = 61.02 cu. in. = 1.057 qts. (U.S. liquid) 1 liter = 0.2642 gal. (U.S. liquid) 1 gal. (U.S.Liq.)= 3.785 liters. 1 bu. (U.S.) . . . .= 35.239 liters 1 gram = 15.43 grains. . = 0.0022 Ibs. avoird. 1 kilogram (kg.)= 2.205 Ibs. avoirdupois. 1 metric ton . ;= 2204.62 Ibs. avoirdupois. TABLE 10 Thermometer Scales There are two thermometer scales in general use in this country at the present time, the Fahrenheit and the Centi- grade. On the Fahrenheit scale the melting point of ice is 32 and the boiling point of water at sea-level is 212. On the Centigrade scale is the melting point of ice and 100 the boiling point of water. Another scale, the Absolute, is sometimes used. This takes its zero at a point assumed to be the lowest temperature that can exist. This point was calculated from the contraction of gases when cooled and found to be 273 C, i. e., 273 below zero Centigrade. The size of the degrees of the Centigrade and Absolute scales is the same, so to con- vert degrees Centigrade to Absolute all that is necessary is to add 273. To convert degrees Centigrade to Fahrenheit multiply by 1.8 and add 32. To convert degrees Fahrenheit to Centigrade, subtract 32 and divide the result by 1.8. Care should^ be taken that the sign of the result is correct when the temperature is below the freezing point of water. (The constant 1.8 is obtained as follows: Between the freezing and boiling points of water there are 100 C and 212 32 = 180 F. Therefore, 1 C = 1.8 F. The factor 32 arises from the fact that C corresponds to 32 F.) 69 /TJ Mensuration Area of triangle=base X % altitude=A X Area parallelogranu=base X altitude=A X B Area of trapezoid=:% (sum of parallel sides) X altitude^ % (A+C) X B Area of a trapezium Divide into triangles and find area of each separately. Diagonal of a 8quare=the square root of twice the square of one side=:1.414 A Diagonal of a rectangle^the square root of the sum of the squares of the adjacent sides. Circumference of a circle^Diameter X 3.1416 rr2 X radius X 3.1416 Area of a circle=The square of the radius X 3.1416 =the square of the diameter X .7854 A regular polygon, one whose sides and angles are all equal, areac=% sum of the sides X per- pendicular from the center to one of the sides. The surface of a sphere=4 X radius squared X 3.1416 Contents of a sphere=4/3 X radius cubed X 3.1416 70 Surface of a cylinder=:area of both ends + length X circumf erenc e. Contents of a cylinder=:area of one end X length. Surface of a cone^area of ..base + circumference of base X % the slant height. Contents of a cone=area of base X % altitude. To square a number multiply it by itself. To cube a number multiply it by itself and multiply the result by the number. INDEX Page Adjustment of Arc Lamps ........ 20 Arc Voltage Enclosed Lamps . . . . 6, 7, 8 Arc Voltage Flame Lamps 29 Striking Point 30 Aluminum. Carrying Capacity .55 Temperature Coefficient 61 Weight 65 Ammeters, Care of 46 Arc Lamp. Adjustment 20 Carbons 13 Connecting to line 14, 30 Dash Pots 19 Gas Caps 16 Globes 12, 15 Suspension . . . . . . . . .41 Wiring 42 See Enclosed Arc Lamps. See Flame Arc Lamps. See Miniature Arc Lamps. See Troubles. Arc Voltage. Enclosed Lamps 6, 7, 8 Flame Lamps 29 Areas, Geometrical Figures 70 Atmospheric Pressure 63 Brass. Temperature Coefficient 61 British Thermal Unit 60 Building Material, Weight of 66 Calorie 60 Carbons. Bridge Core 26 Care of 13, 30 Enclosed Arc Lamp 13 Flame Arc Lamp 29 Graphitization 18 Life 16, 30 Care of Arc Lamps. Enclosed 13, 15 Flame . . . 29, 32 Centigrade Thermometer Scale . . . . . . .69 Centigrade to Fahrenheit 69 Choke Coils 8 Clock Feed Flame Lamps .23 72 INDEX Continued. Clutches. Pa & e Arc Lamp 6, 33 Slipping 20 Colors, Reflecting Power of 34 Columbia Enclosed Arc Carbons 13 Constant Current Apparatus 35 Conversion Factors. Electrical-Mechanical ........ 59 Mechanical-Heat 60 Metric-English 68 Copper. Carrying Capacity . . . . . . . .55 Properties of Copper Wire 56 Temperature Coefficient 61 Weight of 65 Dash Pots, Arc Lamp 19, 33 Dynamos, Arc Lamp . . . . . . . . .35 Economizer 23 Burned out 31 Enclosed Arc Lamps. A. 0. Multiple 7 Carbons ........... 13 D. C. Multiple 5 Gas Caps .16 Series 9 Series-Multiple 10 Twin Carbon 7 Energy, Electrical 59 Fahrenheit Thermometer Scale . . . . . . .69 Fahrenheit to Centigrade ........ 69 Flame Arc Lamps . . . . . . . . .22 Clock Feed 23 Distribution 28 Economizer .......... 23 Efficiency 22 Gravity Feed 25 Magazine 26 Motor Feed 24 Regenerative .......... 27 Force, Work and Power ........ 58 G Gas Caps t 16 Globes. Arc Lamp 12 Cleaning 15 Graphitization of Carbons ........ 18 Gravity Feed Flame Lamp . . . . . . . .25 Grounds on Arc Lamp Circuits 43 78 I N D B X Continued. H Heat. Page Units ........... 60 Mechanical Equivalent of ....... 60 Horse Power Calculations . . . . . . . .62 I Intensified Arc Lamps .......... 11 Intensity of Interior Illumination ...... 34 Jumping of Arc Lamp Carbons . . . . . .19 L Light Reflected by Various Colors Table ..... 34 Line Work ........... 41 Locating Faults ......... 43 M Magazine Flame Lamp ...... . .26 Measuring Instruments, Electrical . . . . .46 Mechanical Equivalent of Heat ....... 60 Mensuration ........... 70 Mercury Arc Rectifier ......... 35 Metals, Weight of ......... 65 Metric System .......... 67 Conversion Factors ........ 68 Miniature Arc Lamps . . . . . . . . .11 Motor Feed Flame Lamp . . . . . . . .25 Motors, Current Required . . . . . . . .57 Multiple Arc Lamps . . . . . . . . . 5, 7 N National Electric Code ......... 48 O Open Circuit on Arc Lamp Circuits ...... 43 P Power Factor ......... . .59 Power, Force and Work ........ 58 Power H.P. Calculations ........ 62 B Regulator, Constant Current ........ 38 Resistance. Calculation of ......... 53 Compensating for Arc Lamps ...... 10 Regulating for Arc Lamps ....... 6 Starting for Arc Lamps ....... 9 S Series Arc Lamps ....... -. . . 9 Series-Multiple Arc Lamps . . . . . . . .10 Short-Life of Carbons ...... . . . 17 Silver Tip Flame Carbons ........ 29 74 I N D E X Continued. Page Size of Wire 52, 56 Station Equipment . . . . . . . . .35 Steel. Temperature Coefficient . . . . . . . .61 Weight 65 Striking Point of Flame Arc Lamps 30 Switch Boards 40 T Temperature. Calculating by Rise in Resistance 61 Thermometer Scales ......... 69 Three-Phase Circuits, Power of 59 Transformers. Auto, for Lamps ......... 8 Constant Current 36, 38 Instrument .......... 47 Trimming Arc Lamps 13 Troubles, Arc Lamp. Burned Out Coils 20 Burned Out Economizer . . . . . . .31 Dirty Carbons 13, 19 Flaming . . . . . . . . . ... 19 Globe Blackening '.15 Graphitization of Carbons . . . . . . .18 Jumping 19 On Arc Lamp Circuits . . . . . . .43 Operating . . . . . . . . . .21 Poor Light 17 Reversed Polarity 15, 30 Short Life 16 Slipping 20, 32 Twin Carbon Lamps 7 Two-Phase Circuits, Power of 59 V Voltmeters, Care of 46 Volumes of Geometrical Figures 70 w Water, Weight of 64 Wattmeters, Care of 46 Weights of Building Material 66 Metals 65 Water 64 Wheatstone Bridge, Use in Locating Faults . . 44 Wire. Calculations of Size 52 Carrying Capacity of Copper Table 55 Properties of Copper Table 56 Wiring. Calculations of Size of Wire 52 Constant Current Apparatus 37, 39 Inside ........... 48 Switchboard, Series Arc Lamp ...... 40 Work, Power and Force 58 75 NATIONAL CARBON COMPANY CLEVELAND, OHIO MANUFACTURERS OF Columbia Carbon Products COLUMBIA ARC CARBONS For open, enclosed and miniature lamps, projectors, headlights, searchlights and photo engraving. SILVER TIP FLAMING CARBONS For flaming arc lamps of all makes. ARC WELDING CARBONS CARBON AND GRAPHITE BRUSHES For all classes of generator and motor service. SPECIAL SHAPES IN CARBON For circuit breaker contacts, lightning arresters, car- bon packing rings for steam turbines, resister car- bons, carbon crucibles. CARBON FOR TELEPHONES Transmitter diaphragms, discs and back plates, granular and globular carbon. CARBON ELECTRODES For arc and resistance electric furnaces. DRY AND WET BATTERIES For all classes of open and closed circuit service. COLUMBIA MULTIPLE BATTERIES For automobile and motor boat ignition and lighting. I 14 DAY USE RETURN TO DESK FROM WHICH BORROWED LOAN DEPT. This book is ripe on the last date stamped below, or rf , ^H me date to which renewed. > I - CO II. P-: i o I >