單項(xiàng)選擇題The purpose of a main switchboard circuit breakers reverse-power trip is to （）.

A.prevent main circuit overload
B.protect the circuit breaker blowout coil
C.prevent alternator motorization
D.prevent low voltage tripout


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1.單項(xiàng)選擇題When you are making a high potential test on a piece of repaired electrical machinery, a rise in leakage current indicates （）.

A.good insulation
B.bad insulation
C.high insulation power factor
D.a high slot discharge factor

2.單項(xiàng)選擇題The sub-multiple prefix "milli" (m) means （）.

A.one thousandth (10 to the -3rd power)
B.one millionth ( 10 to the -6th power)
C.one billionth ( 10 to the -9th power)
D.one trillionth (10 to the -12th power)

3.單項(xiàng)選擇題A “dead front” switchboard is one （）.

A.without switches on it
B.with insulated switches and no exposed terminals
C.without circuit breakers
D.without safety hand nails nor rubber mats

4.單項(xiàng)選擇題The total resistance of a parallel circuit is always （）.

A.larger than the greatest branch resistance
B.smaller than the lowest branch resistance
C.equal to the sum of the individual branch resistances
D.one-half the sum of the individual branch resistances

5.單項(xiàng)選擇題Reduced voltage applied to a motor during the starting period will （）.

A.result in decreased acceleration time only
B.lower the starting current and increase accelerating time
C.cause a greater starting torque
D.increase the starting current and pump capacity