What is the function of a potential relay in a compressor start circuit?

• A. Senses line voltage to disconnect the start winding
• B. Senses current to trigger protection
• C. Regulates refrigerant pressure
• D. Provides overload protection

Answer: (A)

A start device in a single-phase compressor uses a voltage-sensing relay to remove the start winding after the motor has started. The potential relay monitors the line voltage, and once the motor is running and full line voltage is present, it opens the circuit to the start winding. This provides the extra torque needed at start-up but avoids leaving the start winding energized—which would cause overheating and inefficiency. It’s not about regulating refrigerant pressure or providing overload protection, and it’s not the current-sensing type of relay that triggers based on current in the winding.