Fig. 821.—Diagram of an irregular circuit illustrating method of finding the center of distribution. Rule: Divide the sum of the lamp feet for each section by the number of 16 candle power lamps or equivalent in the circuit; the quotient gives the distance in feet from the fuse block to the center of distribution.
In such cases, as shown in [fig. 821], the electrical center can be determined by adding together the lamp feet of the several sections A, B, C, etc., of the main and dividing the result by the 16 c.p. units. Thus the lamp feet of
Section A = 10 lamps × 10 feet = 100 " B = 9 " × 5 " = 45 " C = 7 " × 6 " = 42 " D = 6 " × 4 " = 24 " E = 5 " × 5 " = 25 " F = 4 " × 10 " = 40 " G = 2 " × 5 " = 10 which added together gives a total of 286 lamp feet. This when divided by the ten 16 c.p. units comprising four 16 c.p. lamps and three 32 c.p. lamps, gives a little over 28½ feet as the distance from the fuse block to the center of distribution, the position of which is shown by the line M N in [fig. 821], while that of the geometrical center is shown by the line K L.
| Section | A = 10 | lamps | × 10 | feet | = 100 | |
| " | B = 9 | " | × 5 | " | = 45 | |
| " | C = 7 | " | × 6 | " | = 42 | |
| " | D = 6 | " | × 4 | " | = 24 | |
| " | E = 5 | " | × 5 | " | = 25 | |
| " | F = 4 | " | × 10 | " | = 40 | |
| " | G = 2 | " | × 5 | " | = 10 | |
| which added together gives a total of | 286 | lamp feet. | ||||
When the center of distribution is at a considerable distance from the supply circuit, and it becomes advisable to divide the wiring into two distinct elements—a feeder and one or more mains, the junction of the feeder and the mains should be located at the electrical center of the mains whenever possible. When this is done, it is obvious that the wire size of only one half the main needs to be calculated, as both halves of the main are identical.
Fig. 822.—Brown and Sharpe (B. & S.), or American Standard wire gauge. This gauge was adopted by the brass manufacturers Jan., 1858. The cut is full size, and therefore, shows the actual sizes corresponding to the gauge numbers.
Wire Gauges.—For the purpose of facilitating the measurement of wire, a number of gauges have been designed by various wire manufacturing concerns. The principal gauges used in the United States are the American or Brown & Sharp's gauge; the English standard or Birmingham gauge; Washburn & Moen's standard gauge; Imperial wire gauge; Stubs' steel wire gauge, and the U. S. Standard wire gauge.