It is the principle of the C^2R loss, which the farmer must apply in determining the size of wire he is to use in transmitting his current from the generator switchboard to his house or barn. The wire table on page 159, together with the formula to be used in connection with it, reduce the calculations necessary to simple arithmetic. In this table the resistance of the various sizes of wire is computed from the fact that a wire of pure copper 1 foot long, and 1/1000 inch in diameter (equal to one circular mill) offers a resistance of 10.6 ohms to the foot. The principle of the C^2R loss is founded on Ohm's Law, which is explained in Chapter V. The formula by which the size of transmission wire is determined, for any given distance, and a given number of amperes, is as follows: Distance ft. one way × 22 × No. of amperes circular ------------------------------------------ = mills. Number of volts lost In other words, multiply the _distance in feet_ from mill to house by 22, and multiply this product by the _number of amperes_ to be carried. Then divide the product by the _number of volts_ to be lost; and the result will be the diameter of the wire required _in circular mills_. By referring to the table above, the B. & S. gauge of the wire necessary for transmission, can be found from the nearest corresponding number under the second column, entitled "circular mills area." COPPER WIRE TABLE --------+----------+-----------+-----------+-----------+------------ | | _Area in | _(R) Ohms | | _B.& S. | _Feet | circular | per 1,000 | _Feet | _(R) Ohms Gauge_ | per Lb._ | mills_ | feet_ | per Ohm_ | per pound_ --------+----------+-----------+-----------+-----------+------------ 0000 | 1.561 | 211,600 | .04904 | 20,392.90 | .00007653 000 | 1.969 | 167,805 | .06184 | 16,172.10 | .00012169 00 | 2.482 | 133,079 | .07797 | 12,825.40 | .00019438 0 | 3.130 | 105,534 | .09829 | 10,176.40 | .00030734 1 | 3.947 | 83,694 | .12398 | 8,066.00 | .00048920 2 | 4.977 | 66,373 | .15633 | 6,396.70 | .00077784 3 | 6.276 | 52,634 | .19714 | 5,072.50 | .00123700 4 | 7.914 | 41,742 | .24858 | 4,022.90 | .00196660 5 | 9.980 | 33,102 | .31346 | 3,190.20 | .00312730 6 | 12.58 | 26,250 | .39528 | 2,529.90 | .00497280 7 | 15.87 | 20,816 | .49845 | 2,006.20 | .00790780 8 | 20.01 | 16,509 | .62840 | 1,591.10 | .01257190 9 | 25.23 | 13,094 | .79242 | 1,262.00 | .01998530 10 | 31.82 | 10,381 | .99948 | 1,000.50 | .03178460 11 | 40.12 | 8,234.0 | 1.26020 | 793.56 | .05054130 12 | 50.59 | 6,529.9 | 1.58900 | 629.32 | .08036410 13 | 63.79 | 5,178.4 | 2.00370 | 499.06 | .12778800