Red Seal Electrician Practice
Motor controlsQuestion 228 of 1506

One line to a running three-phase motor opens. What is this destructive condition called?

  1. Jogging duty
  2. Plugging in reverse
  3. Rotor cogging
  4. Single-phasing
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Correct answer: Single-phasing

With one phase lost, the motor keeps trying to run on the other two, which can quickly damage it.

Source: Lessons in Electric Circuits IV: Digital (Kuphaldt), 5.2: Contactors

Practice motor controls

Questions last reviewed: 18 October 2026