DIRECT FEEDING SYSTEMS. 59 
the total drop is that in the principal feeder up to the sub- 
feeder controlling the section in question plus the drop in 
the subfeeder and the trolley wire up to the load. 
The advantage gained by cutting the trolley wire into 
short, independent sections isa certain amount of immunity 
from breakdowns. The subfeeders a, &, ¢, etc., are usually 
provided with fuses or switches or both, so that while in 
case of a break in the trolley wire the cars on the adjacent 
sections are not deprived of current any more than in the 
ladder system, there is no longer the danger of stopping 
traffic by blowing fuses at the station, since the subfeeder 
fuse immediately acts to stop an excessive flow of current. 
In addition, in case of fire or flood affecting any part of 
the system, the disturbed region can be very promptly 
isolated by opening the circuit at the subfeeders. In cities 
A B 
g ] e e il EE 
C D 
= Street Ry. Journal 
F1G. 39. 
  
  
where fires are of frequent occurrence such an arrangement 
is highly necessary, although it is generally desirable to use 
a far more complete feeding system in connection with it. 
Both the arrangements just shown are entirely without 
special provisions for holding up the voltage at distant 
parts of the line, depending practically on the conductivity 
of the principal feeder. 
3. A true feeding system corresponding in a general 
way with Fig. 38 is shown in Fig. 40. Here A B is the 
trolley wire while in multiple with it are feed wires 
tapped into the trolley wire at a, b and o These feeders 
are generally quite independent of each other up to their 
respective junctions with the trolley wire. A load at any 
point, as &, receives its current in both directions through 
the trolley wire, which in turn draws current from the ad- 
jacent feeders. 'The conductivity available at the load & is 
that of the trolley wire from A to 4, reinforced by the feed- 
ers @ and ; in parallel with that of the trolley wire section