A lock-out relay should drop out when which condition occurs?

A lock-out relay should drop out when which condition occurs?

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

Answer: (B)

A lock-out relay functions as a safety interlock that prevents restarting after a fault by latching the control circuit. It stays energized under normal, fault-free conditions, and when a fault occurs, protective devices interrupt the circuit, causing the lock-out to release or drop out. In this case, when the overload relay opens, it breaks the current path that powers the lock-out coil. With the coil de-energized, the lock-out drops out, allowing the system to reset only after the fault is cleared. The thermostat being satisfied just stops demand and doesn’t directly affect the protective interlock. Likewise, short-cycling or the compressor contactor opening are separate behaviors and don’t cause the lock-out to drop out in this protection scheme.

A lock-out relay functions as a safety interlock that prevents restarting after a fault by latching the control circuit. It stays energized under normal, fault-free conditions, and when a fault occurs, protective devices interrupt the circuit, causing the lock-out to release or drop out. In this case, when the overload relay opens, it breaks the current path that powers the lock-out coil. With the coil de-energized, the lock-out drops out, allowing the system to reset only after the fault is cleared. The thermostat being satisfied just stops demand and doesn’t directly affect the protective interlock. Likewise, short-cycling or the compressor contactor opening are separate behaviors and don’t cause the lock-out to drop out in this protection scheme.