The Model 153 Reverse Phase Relay is designed to continuously monitor phase rotation of 3-phase lines. This device should be used in applications where proper phase rotation is critical, such as fan motors, compressors, grinders, elevators, etc. The solid-state sensing circuit drives an internal electromechanical relay which energizes when power, with correct phase rotation, is applied. The relay will not energize if the applied phases are reversed. It will de-energize if phase rotation is reversed while the motor is running. An LED indicator will illuminate with correct ABC phase rotation.