Motor controlsQuestion 7 of 1506

Large breaker trip and close coils are often powered from a 125 V DC battery bank. What is the main reason?

  1. The breaker can still be operated if the AC power fails completely
  2. DC coils pull in with less current than AC coils
  3. DC power removes the need for protective relays
  4. The battery holds the monitored current steady so the relay readings stay accurate
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Correct answer: The breaker can still be operated if the AC power fails completely

A battery bank keeps close and trip power available during an AC power failure.

Source: Lessons in Electric Circuits IV: Digital (Kuphaldt), 5.4: Protective Relays

Practice motor controls

Questions last reviewed: 18 October 2026