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the size of wire to carry 400 16 candle-power 52 volt lamps, each using 1.06 amperes, a distance of 2500 feet, on a loss of 5 per cent, with an initial electro-motive force of 1040 volts. A loss of 5 per cent on a 52-volt lamp is 2.6 volts, and the ratio of conversion is 1949 = 20, whence i_21 x 2500 x 400 x 1.06 2.6 x (20 x 20)

= 21404 = No. 7 wire. SECONDARY CIRCUITS.

The formula for this is A = 21 x D x NxC

1.04

For example: A house is to be connected with secondary mains 110 feet distant, and have current for 23, 52 volt 16 candle-power lamps. Each lamp requires 1.06 amperes, and a loss of 2 per cent is permitted. Then A=21 x Then _21 x 110 x 23 x 1.06

100=54151=No. 3 wire. To accommodate different percentages of loss for both primary and secondary mains the following tables have been inserted. The numbers opposite the figures, indicating the different percentages, are constants which are to be multiplied by the number of lamps, and by the distance (in feet) to get the circular mills of the wire necessary to use.

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EXAMPLES OF PRECEDING TABLE OF

CONSTANTS. .

PRIMARY MAINS. 1. Required size of line wire for 450 52-volt : 16 c. p. lamps, 1200 feet from dynamo; 5 per

cent allowed for loss, on 2080 volts at brushes of dynamo. 450 X 1200 X.005 = 2700 circular mills = No. 16

wire.

(While this size would fill the theoretical requirements, it would be inadvisable to employ such a small size, as the tensile strength would be insufficient to resist the mechanical strains that pole lines are subject to.)

2. Required size of line wire for 1300 52volt, 16 c. p. lamps, 3 miles (15840 feet) from station, with 12 per cent loss. 1300 X 15840 x .008 = 164736 cir. mills = 000 wire.

3. Required size of wire for 280 104-volt lamps, 3400 feet distance, 1040 volts; 8 per cent loss.

280 X 3400 X.15 = 142800 cir. mills = 00 wire.

SECONDARY AND HOUSE MAINS. 1. Required size of wire for 36 52-volt lamps, 106 feet from transformers, 3 per cent loss. 36 x 106 x 13.5 = 51516 cir. mills = No.3 wire.

2. Required size of wire for 2 104-volt lamps, 60 feet from transformer, i per cent loss.

2 X 60 X 12.1 = 14520 cir. mills = No. 9 wire.

3. A cluster of 16 52-volt lamps is 148 feet from transformer; allowing 2 per cent loss, what size of wires to use.

16 X 148 x 20.2 = 47833 cir. mills = No.3 wire.

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21.68 x (100-- per cent. loss in Lanu ps.)

(Resistance of one Lamp)x(per cent. loss in wire.) Circular mils.=K * (mean distance) x (No. of Lamps.)

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