why some contactor doesn’t trip even if a phase goes off
First, the Contactor only doesn’t contain any kind of protection, so, it’s normally do not trip if there’s a missing of a phase, but if the phase’s missing is the same that used to supply the Contactor’s coil, in this case only the Contactor will open.
By the way, if we want to open the Contactor when missing of any phase, we should use a ” Phase Failure Relay ” that can detect :
– Any phase’s missing
– Any phase’s undervoltage ( less than a pre-adjust level )
– Any phase’s overvoltage ( more than a pre-adjust level )
– Direction of 3 phases’ Rotation
and send an order to open the Contactor if any fault of those mentioned above appears.