Phase Failure and Reversal Monitor Relay

If two phases of the supply to a three-phase induction motor are interchanged, themotor will reverse its direction of rotation. This action is called phase reversal. In the operation of elevators and in many industrial applications, phase reversal may result in serious damage to the equipment and injury to people using the equipment.

In other situations, if a fuse blows or a wire to a motor breaks while the motor is running, the motor will continue to operate on single phase but will experience serious overheating. To protect motors against these conditions, phase failure and reversal relays are used.


A solid-state phase monitoring relay is shown This relay provides protection in the event of a voltage unbalance or a phase reversal. The unit automatically resets after the correct voltage conditions

return. An indicating light shows when the relay is activated.