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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. 
 

 
 
 
 
 
 
 
 
 
 
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