How do IEC overload relays protect against single phasing?
A6 Single phasing occurs when power is lost in one of the three legs supplying a motor. Instantly the current through the two remaining phases jumps significantly. Unless promptly disconnected, the two powered windings can soon be destroyed from over-current. IEC overload relays detect single phasing and react before motors can be damaged. The bimetal strips in these devices monitor the current drawn through each of the three phases, bending a proportionate distance. If a phase is lost, the bimetal strip will straighten and, using a double slide-bar ripping mechanism, instantly disconnect the motor from power.
