Re: Phase Control
Protecting a motor with a phase montitor is commonly done, especially on more expensive motors. I always use a phase monitor on submersible motors. I have seen pump stations loose a phase, but the lights would still work, for the operator, its not clear why the pump does not run as the "lights work". I wire a white LED pilot light to the phase monitor, label it CONTROL POWER NORMALLY ON.
A three phase motor may run when single phased, depending the load, with one phase lost, only 57% normal load can be driven, so lightly loaded motors will run.
However, an IEC motor over will offer much better protection from single phasing as the overloads have a differential trip mechanism, such that when a phase is lost, the other two overloads are more responsive to motor current - the motor will draw more current when the phase is lost.
Remember when a phase is lost, the motor will regenerate the missing phase, its hard to find this with a voltmeter, as the voltage will be there, but be off a bit. the only way to know for sure is to deenergize and check incomning power, or use a phase rotation meter.