82 POWER DISTRIBUTION FOR ELECTRIC RAILROADS. 
various values of the constant K which allows for the con- 
ductivity of the track. The distances herein are lengths 
of feeder. =—12 is to be used for continuous rails or the 
most perfect bonding, coupled with moderate service. 
K=13 applies to roads with very fine track and heavy serv- 
ice or to roads with good track and moderate service, 
while K=14 should be used for roads having only ordinary 
track and heavy service or poor track and ordinary traffic. 
K=r14 or 15 may be needed when the track return is un- 
usually poor, while K==11 is introduced for comparison. 
It should be noted that the amount of feed wire needed 
for the case in hand is very different from that indicated in 
the preliminary discussion. This is evidently due to 
the face that the actual wire is adjusted with reference to 
maximum rather than average drop. It is safe in looking 
into the question of distribution, therefore, to figure the 
approximate feeder copper for an assumed maximum load 
varying from twice the assumed average in large and level 
roads to three or even four times the average in small roads 
with heavy grades, 
As to the actual amount of drop to allow circumstances 
vary widely. In most cases the conditions of economy are 
theoretically met by losing five to ten per cent of the total 
energy in the distribution. ‘This means that the average 
drop over the whole system, figured on the average current 
during the hours of operation should be from five to ten 
per cent. Asa matter of fact the average loss is very often 
determined, just as in the case before us, by the condition 
that the maximum net drop shall not exceed a certain fixed 
amount. 'This condition must always be satisfied and it 
seldom leads to an excessive average drop. In the case 
before us the average loss on section 1 is about four per 
cent, on section 2 about six per cent, on section 3 about 
three per cent. ‘The average energy loss, therefore, is a 
  
trifle over 414 per cent. 
Including 42,000 ft. of trolley wire, weighing about 
17,000 1bs, and costing about $2380, the total cost of the 
copper to give the above loss would be, approximately,