Insulated wire for the purpose of winding magnet coils is termed magnet wire. Copper is the material almost universally employed for the conductor. Its high conductivity, great ductility, and low cost are the factors which make it superior to all other metals. However, in special cases, where exceedingly high conductivity is required with a limited winding space, silver wire is sometimes employed, and on the other hand, where very high resistance is desired within a limited winding space, either iron or German silver or some other high-resistance alloy is used.
Wire Gauges. Wire for electrical purposes is drawn to a number of different standard gauges. Each of the so-called wire gauges consists of a series of graded sizes of wire, ranging from approximately one-half an inch in diameter down to about the fineness of a lady's hair. In certain branches of telephone work, such as line construction, the existence of the several wire gauges or standards is very likely to lead to confusion. Fortunately, however, so far as magnet wire is concerned, the so-called Brown and Sharpe, or American, wire gauge is almost universally employed in this country. The abbreviations for this gauge are B.&S. or A.W.G.
TABLE III
Copper Wire Table
Giving weights, lengths, and resistances of wire @ 68° F., of Matthiessen's Standard Conductivity.
| A.W.G. B.&S. | DIAMETER Mils | AREA Circular Mils | RESISTANCE | LENGTH | WEIGHT | |||
| Ohms per Pound | Ohms Per Foot | Feet per Pound | Feet per Ohm | Pounds per Foot | Pounds per Ohm | |||
| 0000 | 460. | 211,600. | 0.00007639 | 0.0000489 | 1.561 | 20,440. | 0.6405 | 13,090. |
| 000 | 409.6 | 167,800. | 0.0001215 | 0.0000617 | 1.969 | 16,210. | 0.5080 | 8,232. |
| 00 | 364.8 | 133,100. | 0.0001931 | 0.0000778 | 2.482 | 12,850. | 0.4028 | 5,177. |
| 0 | 324.9 | 105,500. | 0.0003071 | 0.0000981 | 3.130 | 10,190. | 0.3195 | 3,256. |
| 1 | 289.3 | 83,690. | 0.0004883 | 0.0001237 | 3.947 | 8,083. | 0.2533 | 2,048. |
| 2 | 257.6 | 66,370. | 0.0007765 | 0.0001560 | 4.977 | 6,410. | 0.2009 | 1,288. |
| 3 | 229.4 | 52,630. | 0.001235 | 0.0001967 | 6.276 | 5,084. | 0.1593 | 810.0 |
| 4 | 204.3 | 41,740. | 0.001963 | 0.0002480 | 7.914 | 4,031. | 0.1264 | 509.4 |
| 5 | 181.9 | 33,100. | 0.003122 | 0.0003128 | 9.980 | 3,197. | 0.1002 | 320.4 |
| 6 | 162.0 | 26,250. | 0.004963 | 0.0003944 | 12.58 | 2,535. | 0.07946 | 201.5 |
| 7 | 144.3 | 20,820. | 0.007892 | 0.0004973 | 15.87 | 2,011. | 0.06302 | 126.7 |
| 8 | 128.5 | 16,510. | 0.01255 | 0.0006271 | 20.01 | 1,595. | 0.04998 | 79.69 |
| 9 | 114.4 | 13,090. | 0.01995 | 0.0007908 | 25.23 | 1,265. | 0.03963 | 50.12 |
| 10 | 101.9 | 10,380. | 0.03173 | 0.0009273 | 31.82 | 1,003. | 0.03143 | 31.52 |
| 11 | 90.74 | 8,234. | 0.05045 | 0.001257 | 40.12 | 795.3 | 0.02493 | 19.82 |
| 12 | 80.81 | 6,530. | 0.08022 | 0.001586 | 50.59 | 630.7 | 0.01977 | 12.47 |
| 13 | 71.96 | 5,178. | 0.1276 | 0.001999 | 63.79 | 500.1 | 0.01568 | 7.840 |
| 14 | 64.08 | 4,107. | 0.2028 | 0.002521 | 80.44 | 396.6 | 0.01243 | 4.931 |
| 15 | 57.07 | 3,257. | 0.3225 | 0.003179 | 101.4 | 314.5 | 0.009858 | 3.101 |
| 16 | 50.82 | 2,583. | 0.5128 | 0.004009 | 127.9 | 249.4 | 0.007818 | 1.950 |
| 17 | 45.26 | 2,048. | 0.8153 | 0.005055 | 161.3 | 197.8 | 0.006200 | 1.226 |
| 18 | 40.30 | 1,624. | 1.296 | 0.006374 | 203.4 | 156.9 | 0.004917 | 0.7713 |
| 19 | 35.89 | 1,288. | 2.061 | 0.008038 | 256.5 | 124.4 | 0.003899 | 0.4851 |
| 20 | 31.96 | 1,022. | 3.278 | 0.01014 | 323.4 | 98.66 | 0.003092 | 0.3051 |
| 21 | 28.46 | 810.1 | 5.212 | 0.01278 | 407.8 | 78.24 | 0.002452 | 0.1919 |
| 22 | 25.35 | 642.4 | 8.287 | 0.01612 | 514.2 | 62.05 | 0.001945 | 0.1207 |
| 23 | 22.57 | 509.5 | 13.18 | 0.02032 | 648.4 | 49.21 | 0.001542 | 0.07589 |
| 24 | 20.10 | 404.0 | 20.95 | 0.02563 | 817.6 | 39.02 | 0.001223 | 0.04773 |
| 25 | 17.90 | 320.4 | 33.32 | 0.03231 | 1,031. | 30.95 | 0.0009699 | 0.03002 |
| 26 | 15.94 | 254.1 | 52.97 | 0.04075 | 1,300. | 24.54 | 0.0007692 | 0.1187 |
| 27 | 14.2 | 201.5 | 84.23 | 0.05138 | 1,639. | 19.46 | 0.0006100 | 0.01888 |
| 28 | 12.64 | 159.8 | 133.9 | 0.06479 | 2,067. | 15.43 | 0.0004837 | 0.007466 |
| 29 | 11.26 | 126.7 | 213.0 | 0.08170 | 2,607. | 12.24 | 0.0003836 | 0.004696 |
| 30 | 10.03 | 100.5 | 338.6 | 0.1030 | 3,287. | 9.707 | 0.0003042 | 0.002953 |
| 31 | 8.928 | 79.70 | 538.4 | 0.1299 | 4,145. | 7.698 | 0.0002413 | 0.001857 |
| 32 | 7.950 | 63.21 | 856.2 | 0.1638 | 5,227. | 6.105 | 0.0001913 | 0.001168 |
| 33 | 7.080 | 50.13 | 1,361. | 0.2066 | 6,591. | 4.841 | 0.0001517 | 0.0007346 |
| 34 | 6.305 | 39.75 | 2,165. | 0.2605 | 8,311. | 3.839 | 0.0001203 | 0.0004620 |
| 35 | 5.615 | 31.52 | 3,441. | 0.3284 | 10,480. | 3.045 | 0.00009543 | 0.0002905 |
| 36 | 5.0 | 25.0 | 5,473. | 0.4142 | 13,210. | 2.414 | 0.00007568 | 0.0001827 |
| 37 | 4.453 | 19.83 | 8,702. | 0.5222 | 16,660. | 1.915 | 0.00006001 | 0.0001149 |
| 38 | 3.965 | 15.72 | 13,870. | 0.6585 | 21,010. | 1.519 | 0.00004759 | 0.00007210 |
| 39 | 3.531 | 12.47 | 22,000. | 0.8304 | 26,500. | 1.204 | 0.00003774 | 0.00004545 |
| 40 | 3.145 | 9.888 | 34,980. | 1.047 | 33,410. | 0.9550 | 0.00002993 | 0.00002858 |
In the Brown and Sharpe gauge the sizes, beginning with the largest, are numbered 0000, 000, 00, 0, 1, 2, and so on up to 40. Sizes larger than about No. 16 B.&S. gauge are seldom used as magnet wire in telephony, but for the purpose of making the list complete, Table III is given, including all of the sizes of the B.&S. gauge.
In Table III there is given for each gauge number the diameter of the wire in mils (thousandths of an inch); the cross-sectional area in circular mils (a unit area equal to that of a circle having a diameter of one one-thousandth of an inch); the resistance of the wire in various units of length and weight; the length of the wire in terms of resistance and of weight; and the weight of the wire in terms of its length and resistance.