A protective relay that monitors three-phase power supply and disconnects the elevator if a phase is lost, reversed, or unbalanced.
Full Definition
Elevator traction motors require a correctly phased, balanced three-phase supply. A phase failure relay continuously monitors the supply for phase loss (one phase missing), phase reversal (incorrect sequence), and significant voltage imbalance between phases. On detection of any fault, it opens the main contactor, bringing the elevator to a controlled stop and preventing motor damage or incorrect motor rotation that could cause the car to move in the wrong direction. Phase failure relays are mandatory under EN 81-20 and IEC 60947 for three-phase elevator drives.
