A current magnetic relay opens and closes its contacts based on the ________.

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Multiple Choice

A current magnetic relay opens and closes its contacts based on the ________.

A current magnetic relay uses the current in the run winding as its control signal. At startup, the run-winding current is high, which keeps the relay energized and the starting circuit (start winding or capacitor) in place to provide the needed torque. As the motor speeds up, back-EMF reduces the current in the run winding, and once that current drops to a set level, the relay de-energizes and disconnects the starting circuit. This behavior makes the run-winding current the best indicator for when to open or close the contacts. Frequency of the supply isn’t the controlling factor, and starting current in the start winding wouldn’t reliably reflect the motor’s speed once running.

A current magnetic relay uses the current in the run winding as its control signal. At startup, the run-winding current is high, which keeps the relay energized and the starting circuit (start winding or capacitor) in place to provide the needed torque. As the motor speeds up, back-EMF reduces the current in the run winding, and once that current drops to a set level, the relay de-energizes and disconnects the starting circuit. This behavior makes the run-winding current the best indicator for when to open or close the contacts. Frequency of the supply isn’t the controlling factor, and starting current in the start winding wouldn’t reliably reflect the motor’s speed once running.

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