单项选择题

The main difference between a motor control circuit containing low voltage protection and low voltage release is that the latter contains （）.

A.a magnetic operating coil
B.normally open line contacts
C.thermal-overload protection
D.a momentary-contact start button

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单项选择题

What will be the phase angle relationship of a six-pole, three-phase, rotating field generator （）.

A.60
B.120
C.180
D.360

单项选择题

The part of a fuse that melts and opens the circuit is made of （）.

A.copper and antimony
B.steel and babbitt
C.aluminum or beryllium alloy
D.zinc or an alloy of tin and lead

单项选择题

Time delayed or delayed action-type fuses are designed to （）.

A.prevent grounds in branch circuits
B.prevent opens in motor circuits
C.permit momentary overloads without melting
D.guard lighting and electronic circuits