When does the coil in a magnetic motor starter de-energize?

In a magnetic motor starter, the coil de-energizes when an overload condition is detected. This mechanism is critical for protecting the motor from damage due to excessive current, which can occur during stalls or mechanical jams. The overload relay is designed to monitor the current flowing to the motor. If this current exceeds a predetermined limit for a specific duration, the relay will trip, removed the power from the coil of the magnetic starter. This action opens the starter contacts, disconnecting the motor from its power source and preventing overheating and potential failure of the motor.

Recognizing that overload protection is essential for motor longevity helps clarify why this specific condition is the trigger for de-energizing the coil. Other current types, such as short-circuit or ground-fault currents, have different protective responses and mechanisms that may engage other safety devices but do not directly influence the coil's operation in the same manner as an overload.