Hawkins Electrical Guide v. 04 (of 10) / Questions, Answers, & Illustrations, A progressive course of study for engineers, electricians, students and those desiring to acquire a working knowledge of electricity and its applications

by N. Hawkins

or using the usual symbols

E = I × feet × 10.8 circular mils . . . . (3)

or expressed in words, formula (3) means that the volts lost or drop between the beginning and end of a circuit is equal to the current flowing through the circuit multiplied by the product of the conductors' length in feet multiplied by the resistance of one mil foot of wire, divided by the area of the conductor in circular mils.

LAMP TABLE FOR WEATHER PROOF WIRES

Showing the maximum number of 16 candle power 120 to 240 volt lamps in parallel that may be carried by various sizes of weather proof wire without violating the underwriters' rules.

Wire size B. & S. gauge	Amperes.	3.1.watt lamps.		3.5.watt lamps.		4.watt lamps.
		110 V.	220 V.	110 V.	220 V.	220 V.	230 V.	240 V.
0000	312	686	1372	612	1225	1072	1121	1170
000	262	576	1152	514	1029	900	941	982
00	220	484	968	432	864	756	790	825
0	185	407	814	363	726	636	665	693
1	156	343	686	306	612	536	560	585
2	131	288	576	257	514	450	470	491
3	220	242	484	216	432	378	395	412
4	92	202	404	180	361	316	330	345
5	77	169	338	151	302	264	276	288
6	65	143	286	127	255	223	233	243
8	46	101	202	90	180	158	165	172
10	32	70	140	62	125	110	115	120
12	23	50	101	45	90	79	82	86
14	16	35	70	31	62	55	57	60

Now, since the length of the circuit is given as the "run" or distance one way, that is, one half the total length of wire in the circuit, formula (3) must be multiplied by 2 to get the total drop, that is:

E = I × feet × 10.8 X 2 circular mills = I × feet × 21.6 circular mills . . . . (4)

Solving the last equation for the unknown quantity, the following equation is obtained for size of wire:

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