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ELECTRICAL CONDUCTORS
65
wire of one mil cross-section area has a resistance of 10.5 ohms, then 400 feet will have 400 X 10.5 = 4200 ohms resistance. However, the resistance of a wire of given length decreases as its diameter increases. Table
TABLE NO. 4 RESISTANCE OF COPPER WIRE AT NORMAL TEMPERATURE
Resistance at 75° F., Internationa
Units
Ohms
Ohms
Feet
Am. Gauge,
per
Per
per
B. & S. No.
1000 Feet
Mile
Ohm
Ohms per Lb.
0000
0.04964
0.2621
20147.
0.00007758
000
0.06261
0.3306
15972.
0.0001234
00
0.07894
0.4168
12668.
0.0001962
0
0.09945
0.5251
10055.
0.0003114
1
0.1255
0.6627
7968.
0.0004960
2
0.1583
0.8360
6316.
0.0007894
3
0.1966
1.054
5010.
0.001254
4
0.2516
1.329
3974.
0.001994
5
0.3174
1.676
3150.
0.003173
6
0.4002
2.113
2499.
0.005043
7
0.5044
2.663
1982.
0.008013
8
0.6361
3.358
1572.
0.01274
9
0.8026
4.238
1246.
0.02029
10
1.011
5.340
988.8
0.03220
11
1.277
6.743
783.1
0.05135
12
1.609
8.496
621.5
0.08154
13
2.026
10.70
493.6
0.1293
14
2.556
13.50
391.2
0.2058
15
3.221
17.01
310.4
0.3268
16
4.070
21.49
245 7
0.5216
17
5.118
27.02
195.4
0.8249
18
6.466
34.14
154.6
1.317
19
8.151
43.04
122.7
2.092
20
10.26
54.15
97.51
3.312
21
12.93
68.26
77.35
5.263
22
16.41
86.62
60.95
8.476
23
20.56
108.6
48.63
13.32
24
26.00
137.3
38.47
21.28
25
32.78
173.1
30.51
33.84
26
41.54
219.4
24.07
54.35
27
52.09
275.0
19.20
85.44
28
66.17
349.4
15.11
137.9
29
82.27
434.4
12.15
213.1
30
105.1
554.7
9.519
347.6
31
131.7
695.4
7.592
546.3
32
166.2
877.4
6.018
869.6
33
209.5
1106.
4.772
1383.
34
264.6
1397.
3.779
2205.
35
333.7
1762.
2.996
3507.
36
420.1
2218.
2.380
5558.
37
530.4
2801.
1.885
8860.
38
669.9
3537.
1.493
14131.
39
843.0
4451.
1.186
22378.
40
1065.
5625.
0.9387
35734.
No. 2 shows that a No. 6 wire is 162 mils in diameter and has a cross section area of 26,250 C. M. (circular mils). It follows that the resistance of our 400 feet of No. 6 wire would be equal to the resistance of 400 feet of 1-mil wire (4,200 ohms) divided by the cross-section