The relays operate when all the phases are present and the phase sequence is correct. Contact but the motor starter or contactor will not energize until either a START pushbutton is closed or a two-wire control unit ie limit switch proximity switch relay contact etc is closed. In the above diagram I have shown the complete method of wiring or connection of phase failure relay diagram with circuit breaker cont actor overload relay push-button switches and electric motor however lets talk about this step by step.
There is a voltage failure and will pick up again as soon as voltage returns.
PAHA PAHI 4 wire. Reference to the diagram below will show how this occurs. The output relay is energized when all three phase voltages are present and the phase conditions voltage and phase sequence are correct. The phase failure relay monitors phase sequence phase break and undervoltage.