NOTE.—In some cases where the capacity of the plant is not very great, the oil switch is mounted on the back of the panel, and the bus bars, current transformers, &c., on the framework, also just at the back of the panel, but under no circumstances, in good modern practice, is high pressure apparatus permitted on the front of the board. Where the capacity of the plant is very large, the oil switches are operated electrically by means of small motors, and in this case the small switch gear for starting and stopping this motor is mounted on the generator panel, also the lamp or lamps to indicate when the switch is open, and when closed.
CHAPTER LXV
ALTERNATING CURRENT WIRING
In the case of alternating current, because of its peculiar behaviour, there are several effects which must be considered in making wiring calculations, which do not enter into the problem with direct current.
Accordingly, in determining the size of wires, allowance must be made for
1. Self-induction;
2. Mutual-induction;
3. Power factor;
4. Skin effect;
5. Corona effect;
6. Frequency;
7. Resistance.
Most of these items have already been explained at such length, that only a brief summary of facts need be added, to point out their connection and importance with alternating current wiring.
Induction.—The effect of induction, whether self-induction or mutual induction, is to set up a back pressure of spurious resistance, which must be considered, as it sometimes materially affects the calculation of circuits even in interior wiring.