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Connecting a capacitor across a motor that may be left to coast risks

  • A.self-excitation and a dangerous overvoltage
  • B.a permanent reduction in the motor's efficiency
  • C.the capacitor discharging into the supply
  • D.a rise in the motor's starting current

Answer: A

The still-rotating machine and the capacitor form a self-excited generator whose voltage can rise well above nominal and damage both. Sizing the capacitor below the motor's magnetising current, and switching it with the motor, prevents it.

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