Ques. How is the four pole main switch wired?
Ans. Its two central terminals which connect directly with the line wires, are joined together by a conductor, and from this point one wire is led off. This wire, together with the two outside wires, form the feeders of the system.
Ques. How many voltmeters are required for the two phase system?
Ans. One voltmeter is sufficient on the board if a proper switching device be employed to shift its connections across either of the two circuits; otherwise, two voltmeters will be necessary, one bridged across each of these respective circuits.
The same reasoning holds true in regard to ground detectors, so that one or two of these will be required, depending upon the aforementioned conditions.
Ques. What are the essential points of difference between the single phase switchboard wiring as shown in [fig. 2,820], and that required for a three wire three phase system?
Ans. The three phase system requires the use of a three pole switch in place of the two pole switch; the insertion of an ammeter, a circuit breaker, and a compensator in each of the three wires of the system; the presence of two ground detectors instead of one, and the addition of a voltmeter switch if but one voltmeter be provided, or else the installation of two voltmeters, connected the one between the middle wire and outer right hand wire, and the other between the middle wire and outer left hand wire.
Fig. 2,830.—Diagram of switchboard connections for General Electric automatic voltage regulator with two exciters and two alternators.