单项选择题
A.neutralize armature reaction B.conduct electric current to an outside circuit C.convert DC current to AC current D.provide excitation to a DC generator
A.Open the machine on both ends so as to allow the air and dust to escape B.Be certain that the circuit breaker is opened and tagged on the feeder panel C.Be certain that the air is clean and as dry as possible D.All of the above
A.higher than that of copper B.lower than that of copper C.equal to that of copper D.reached when the conductor it is protecting becomes "white hot"