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

TABLE OF WIRE EQUIVALENTS

GAUGE B. & S.	NUMBER OF WIRES
	2	4	8	1 6	3 2	6 4	1 2 8	2 5 6	5 1 2	1 0 2 4	2 0 4 8	4 0 9 6	8 1 9 2	1 6 3 8 4
0000	0	3	6	9	12	15	18	21	24	27	30	33	36	39
000	1	4	7	10	13	16	19	22	25	28	31	34	37	40
00	2	5	8	11	14	17	20	23	26	29	32	35	38	0+6
0	3	6	9	12	15	18	21	24	27	30	33	36	39	1+7
1	4	7	10	13	16	19	22	25	28	31	34	37	40	2+8
2	5	8	11	14	17	20	23	26	29	32	35	38	3+9	4+6
3	6	9	12	15	18	21	24	27	30	33	36	39	4+10	5+7
4	7	10	13	16	19	22	25	28	31	34	37	40	5+11	6+8
5	8	11	14	17	20	23	26	29	32	35	38	6+12	7+9
6	9	12	15	18	21	24	27	30	33	36	39	7+13	8+10
7	10	13	16	19	22	25	28	31	34	37	40	8+14	9+11
8	11	14	17	20	23	26	29	32	35	38	9+15	10+12
9	12	15	18	21	24	27	30	33	36	39	10+16	11+13
10	13	16	19	22	25	28	31	34	37	40	11+17	12+14
11	14	17	20	23	26	29	32	35	38	12+18	13+15
12	15	18	21	24	27	30	33	36	39	13+19	14+16
13	16	19	22	25	28	31	34	37	40	14+20	15+17
14	17	20	23	26	29	32	35	38	15+21	16+18
15	18	21	24	27	30	33	36	39	16+22	17+19
16	19	22	25	28	31	34	37	40	17+23	18+20
17	20	23	26	29	32	35	38	18+24	19+21
18	21	24	27	30	33	36	39	19+25	20+22
19	22	25	28	31	34	37	40	20+26	21+23
20	23	26	29	32	35	38	21+27	22+24
21	24	27	30	33	36	39	22+28	23+25
22	25	28	31	34	37	40	23+29	24+26
23	26	29	32	35	38	24+30	25+27
24	27	30	33	36	39	25+31	26+28
25	28	31	34	37	40	26+32	27+29
26	29	32	35	38	27+33	28+30
27	30	33	36	39	28+34	29+31
28	31	34	37	40	29+35	30+32
29	32	35	38	30+36	31+33
30	33	36	39	31+37	32+34
31	34	37	40	32+38	33+35
32	35	38	33+39	34+36
33	36	39	34+40	35+37
34	37	40	36+39
35	38	37+39
36	39	38+40
37	40

Ques. If the calculated size of wire be larger than any in the table how is the required area obtained?

Ans. By using two or more smaller wires in parallel, whose combined area is equal to the required area.

To facilitate finding the equivalent sizes the above table of wire equivalents has been prepared.

Ques. How is the table of wire equivalents used?

Ans. To use the table, find in the vertical column at left the size of conductor desired; then follow along horizontally until the size of wire that is desired to use for the strands, and the corresponding number at top of column will give the number of strands of that size wire required.

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Fig. 832.—Break down switch for use on three wire circuit, enabling it to be operated break down fashion with the two outers connected together and the neutral wire serving as one side of the resultant two wire circuit. Such circuits must be figured as two wire installations of one half the three wire voltage. The size of the neutral wire of a three wire circuit depends on conditions of operation. Three wire circuits for occasional two wire working, must have a neutral wire whose cross section is equal to the combined cross sections of the two outer wires. This plan is useful for buildings supplied from a central station, as it will be satisfactory for two wire operation in emergencies, and for three wire, two phase or three phase distribution should the central station ultimately be changed over to either of those alternating current systems. The expense for the extra copper in the beginning will not be nearly so great as that entailed by a change in the wiring later on should developments require it. It is permissible, however, to make the cross section of the neutral wire smaller than that of each outer wire, if one be reasonably sure that there will never be any changes such as those just mentioned, and if the drop in the two outer wires do not exceed 1½ per cent. Under such conditions, it will be found a very good rule to calculate the neutral wire of a principal feeder for a maximum unbalancing of 25 per cent, that is, a condition under which the current in one outer wire will be 75 per cent of the current in the other one, the current in the neutral being 25 per cent of that in the heavier loaded outer wire.

Ques. What is the significance of the zig-zag line?