where
L = inductance of a loop of a three phase circuit in henrys.
Note.—The inductance of a complete single phase circuit = L × 2 ÷ √3.
A = distance between wires;
d = diameter of wire.
| Size B.&S. | Diam. (inches) | Distance d (inches) | Capacity C (μfarads) |
|---|---|---|---|
| 0000 | .46 | 12 | .0226 |
| 18 | .0204 | ||
| 24 | .01922 | ||
| 48 | .01474 | ||
| 000 | .41 | 12 | .0218 |
| 18 | .01992 | ||
| 24 | .01876 | ||
| 48 | .01638 | ||
| 00 | .365 | 12 | .0124 |
| 18 | .01946 | ||
| 24 | .01832 | ||
| 48 | .01604 | ||
| 0 | .325 | 12 | .02078 |
| 18 | .01898 | ||
| 24 | .01642 | ||
| 48 | .01570 | ||
| 1 | .289 | 12 | .02022 |
| 18 | .01952 | ||
| 24 | .01748 | ||
| 48 | .0154 | ||
| 2 | .258 | 12 | .01972 |
| 18 | .01818 | ||
| 24 | .01710 | ||
| 48 | .01510 | ||
| 3 | .229 | 12 | .01938 |
| 18 | .01766 | ||
| 24 | .01672 | ||
| 48 | .01480 | ||
| 4 | .204 | 12 | .01874 |
| 18 | .01726 | ||
| 24 | .01636 | ||
| 48 | .01452 | ||
| 5 | .182 | 12 | .01830 |
| 18 | .01690 | ||
| 24 | .01602 | ||
| 48 | .01426 | ||
| 6 | .162 | 12 | .01788 |
| 18 | .01654 | ||
| 24 | .01560 | ||
| 48 | .0140 | ||
| 7 | .144 | 12 | .01746 |
| 18 | .01618 | ||
| 24 | .01538 | ||
| 48 | .01374 | ||
| 8 | .128 | 12 | .01708 |
| 18 | .01586 | ||
| 24 | .01508 | ||
| 48 | .01350 | ||
| 9 | .114 | 12 | .01660 |
| 18 | .01552 | ||
| 24 | .01478 | ||
| 48 | .01326 | ||
| 10 | .102 | 12 | .01636 |
| 18 | .01522 | ||
| 24 | .01452 | ||
| 48 | .01304 |
Capacity.—In any given system of electrical conductors, a pressure difference between two of them corresponds to the presence of a quantity of electricity on each. With the same charges, the difference of pressure may be varied by varying the geometrical arrangement and magnitudes and also by introducing various dielectrics. The constant connecting the charge and the resulting pressure is called the capacity of the system.
All circuits have a certain capacity, because each conductor acts like the plate of a condenser, and the insulating medium, acts as the dielectric. The capacity depends upon the insulation.
For a given grade of insulation, the capacity is proportional to the surface of the conductors, and universally to the distance between them.
A three phase three wire transmission line spaced at the corners of an equilateral triangle as regards capacity acts precisely as though the neutral line were situated at the center of the triangle.