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Electrician Red Seal · Question

During a routine inspection, a technician notices that the shading coil on an AC magnetic contactor's armature is broken. What is the likely operational consequence of this fault?

The shading coil in an AC contactor creates a phase lag in a portion of the magnetic flux, preventing the magnetic force from dropping to zero during the AC cyc

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Question: During a routine inspection, a technician notices that the shading coil on an AC magnetic contactor's armature is broken. What is the likely operational consequence of this fault?

Answer options:

  • The contactor will fail to close its main contacts. ✅ The contactor will hum or chatter excessively when energized.
  • The contactor will operate silently but with reduced pulling force.
  • The contactor's coil will draw excessive current and overheat.

Correct answer: The contactor will hum or chatter excessively when energized.

Explanation: The shading coil in an AC contactor creates a phase lag in a portion of the magnetic flux, preventing the magnetic force from dropping to zero during the AC cycle. A broken shading coil causes the contactor to hum or chatter as the armature attempts to hold in with an inconsistent magnetic field.

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