A lock-out relay should drop out when:

A lock-out relay should drop out when:

• A. The compressor short-cycles
• B. The compressor contactor opens
• C. The thermostat is satisfied
• D. An overload relay opens

Answer: (D)

A lock-out relay is a protective interlock that prevents the compressor from restarting after a fault. It stays energized during normal operation, but if the motor’s overload protector opens, that fault interrupts the control circuit. With the control power lost, the lock-out relay releases and drops out, keeping the compressor off until the fault is cleared and the circuit is reset. The other scenarios—short-cycling, the contactor opening, or the thermostat simply being satisfied—do not represent the fault condition that warrants a lock-out release and therefore do not cause it to drop out by design.

A lock-out relay is a protective interlock that prevents the compressor from restarting after a fault. It stays energized during normal operation, but if the motor’s overload protector opens, that fault interrupts the control circuit. With the control power lost, the lock-out relay releases and drops out, keeping the compressor off until the fault is cleared and the circuit is reset. The other scenarios—short-cycling, the contactor opening, or the thermostat simply being satisfied—do not represent the fault condition that warrants a lock-out release and therefore do not cause it to drop out by design.