DIRECT FEEDING SYSTEMS. 57 
from time to time, but yet closely confined to that area; 
railway feeders must be so designed as to meet not only a 
load variable in amount from second to second, but shifting 
from place to place obedient to causes that follow no definite 
law. On the other hand not only are railway feeders 
absolved from the necessity of holding the voltage closely 
uniform, but by virtue of this they can the more easily be 
arranged to meet extreme shifting of the load. 
In early electric railways the trolley wire proper was 
rather small and the feeding was often relatively quite as 
complex as that in large modern systems. 
The conditions which must be met in planning a direct 
feeding system are roughly as follows: 
1. The maximum fall in voltage at any point in the 
system under all working conditions must not exceed a 
fixed amount. 
2. The average drop throughout the system under 
normal conditions must equal a certain predetermined 
amount. 
3. The feeders must be so connected that accidents 
to the working conductors shall interfere with traffic to as 
small an extent as possible. 
To meet these various conditions a large number of 
arrangements of feeders have been devised, many of which 
are in txtensive use. The following are some of the most 
usual, which have stood the test of experience. 
1. The so-called ladder system shown in Fig. 38. Here 
one pole of the dynamo is earthed as usual and the other 
is connected to the trolley wire C D, and also to the feeder 
A B. These are connected at intervals of a few hundred 
feet by subfeeders @, &, ¢, d, ¢, [, etc., which are generally 
hardly more than tie wires uniting the principal feeder to 
the trolley wire. ‘This arrangement was very common in 
early electric roads. It made possible the use of a very 
slender trolley wire merely large enough to carry conven- 
iently the current for cars running between the subfeeders, 
and made the system tolerably free from interruption by 
accidents to the trolley wire, which from its small size was