This section is from the book "A Treatise On Architecture And Building Construction Vol3: Stair Building, Ornamental Ironwork, Roofing, Sheet-Metal Work, Electric-Light Wiring And Bellwork", by The Colliery Engineer Co.. Also available from Amazon: A Treatise On Architecture And Building Construction.
Feeders are conductors supplying current to single terminal points or distributing centers, running directly from the source of current to those points without any branches or other connections throughout their length.
Mains are conductors which are tapped at many points for supply of current to branch circuits. In Fig. 31 the heavy lines a b, c e are the mains, and m n, r p, ml n 1 , r1p1 are the feeders extending from the dynamos d, d1 to the mains. These latter are tapped at any desired points for the branch circuits l, l, l.
43. There must always be some drop in potential along the conductors, as has already been pointed out, but it is of the utmost importance that the drop from the dynamo or street mains to the lamps at any point of the system should be uniform, so that all the lamps may burn at the same degree of brilliancy. If the drop to one set of lamps were 2 volts, and to another set 5 volts, then when the first was burning brightly, the second would be 3 volts below its required voltage, and the lamps would appear quite dim. The amount of drop usually allowed is about 5 per cent., and this is divided over the feeders and mains and branches according to their length, or as special conditions may warrant.