單項選擇題An accidental path of low resistance, allowing passage of abnormal amount of current is known as a/an（）.

A.open circuit
B.short circuit
C.polarized ground
D.ground reference point


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1.單項選擇題Which of the following statements represents the main difference between a relay and a contactor?（）

A.Contactors control current and relays control voltage
B.A relay is series connected and a contactor is parallel connected
C.Contactors can handle heavier loads than relays
D.Contactors are made from silver and relays are made from copper

2.單項選擇題Any electric motor can be constructed to be（）.

A.short proof
B.ground proof
C.explosion proof
D.overload proof

3.單項選擇題The output voltage of a 440 volt, 60 hertz, AC generator is controlled by the （）.

A.prime mover speed
B.exciter output voltage
C.load on the alternator
D.number of poles

4.單項選擇題A ground can be defined as an electrical connection between the wiring of a motor and its（）.

A.shunt field
B.circuit breaker
C.metal framework
D.inter-pole

5.單項選擇題Brushless generators are designed to operate without the use of（）.

A.brushes
B.slip rings
C.commutators
D.all of the above