Red Seal Electrician Practice
Motor controlsQuestion 111 of 1506

What is interlocking in a motor control circuit?

  1. Using a seal-in contact to keep the contactor on after the start
  2. Using overload heaters to cool the contactor during a long run
  3. Connecting both contactors in parallel to share the load
  4. Energizing one contactor prevents the other from being energized
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Correct answer: Energizing one contactor prevents the other from being energized

It is done with auxiliary contacts on each contactor.

Source: Lessons in Electric Circuits IV: Digital (Kuphaldt), 6.3: Permissive and Interlock Circuits

Practice motor controls

Questions last reviewed: 18 October 2026