A potential relay is an electromagnetic switching device that removes a motor start capacitor from the circuit once the motor reaches approximately 70% of full speed. This relay responds to voltage changes across the motor windings rather than current flow. Potential relays are commonly used in air conditioning compressors and heat pump systems to ensure efficient motor operation.
Operating Principle
As motor speed increases during startup, voltage across the run winding drops while voltage across the start winding decreases more rapidly. The potential relay coil senses this voltage differential and triggers contacts that disconnect the start capacitor. Most potential relays operate on voltage ranges between 250V and 600V, depending on system specifications.
Comparison to Current Relays
Potential relays provide more precise motor control than current relays because they respond to voltage rather than amperage. This design prevents start capacitor discharge during operation and reduces electrical stress on motor windings. Potential relays are preferred for capacity-modulating compressors where precise control improves efficiency and extends equipment lifespan.