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單項(xiàng)選擇題

Ammeters and voltmeters used in sinusoidal AC power systems indicate which of the following values of the waveforms measured?（）

A.Peak value
B.Root-mean-square value
C.Average value
D.Maximum value

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單項(xiàng)選擇題

Fuses placed in series with a thermal trip-type circuit breaker are used for （）.

A.time-delay protection
B.short-circuit protection
C.short duration surge protection
D.sustained overload protection

單項(xiàng)選擇題

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