Which two relays are used to start a single-phase hermetic compressor?

Which two relays are used to start a single-phase hermetic compressor?

• A. Magnetic relay and solid-state relay
• B. Potential relay and current relay
• C. Thermal relay and pressure relay
• D. Pneumatic relay and vacuum relay

Answer: (B)

Starting a single-phase hermetic compressor needs a brief energizing of the start winding and then a quick removal of that winding once the motor is turning. To achieve this reliably, two relays work together: a potential relay and a current relay. The potential relay senses the line voltage and helps energize the start winding when the voltage is applied, creating the needed rotating field to get the compressor moving. The current relay watches the current in the circuit and, as the motor speeds up and the start winding current naturally falls, it opens to remove the start winding from the circuit. This coordinated action lets the compressor start smoothly and then run on the run winding alone. Other options don’t provide this two-stage start control in standard hermetic compressors.

Starting a single-phase hermetic compressor needs a brief energizing of the start winding and then a quick removal of that winding once the motor is turning. To achieve this reliably, two relays work together: a potential relay and a current relay. The potential relay senses the line voltage and helps energize the start winding when the voltage is applied, creating the needed rotating field to get the compressor moving. The current relay watches the current in the circuit and, as the motor speeds up and the start winding current naturally falls, it opens to remove the start winding from the circuit. This coordinated action lets the compressor start smoothly and then run on the run winding alone. Other options don’t provide this two-stage start control in standard hermetic compressors.