Undervoltage Relays

Perhaps the application to which you refer is simply a single phase circuit. There are also three phase voltage monitors. You can buy as many features as you desire for those devices. That includes under voltage, over voltage, phase loss or imbalance, phase reversal, over frequency, under frequency, and ground fault. I hope that gives you enough ideas.

And sometimes people use a type of relay that monitors only one phase, but is set up so that an imbalance caused by a loss of either of the other two will be something the relay will detect and trip on. It works, but the relay has to be very sensitive and thus prone to nuisance tripping from disturbances caused by normal operations. I prefer to monitor all 3 phases for both voltage and current.

Pls anybody can provide more insight into this?

The most obvious reason I can think of is cost savings. Nothing else. It would be more prudent to use at least two undervoltage relays - one connected across 'R' & 'Y' and the other connected across 'Y' & 'B'. Still better would be to connect three relays rated at 240 V, connected between each phase & neutral - provided your network source is star connected.

Check out this link.

Anybody pls...........those relays were of english electric make VAGM.....

Jeez... quit begging.

***** you....You forced me to tell this