This device will only energize the relay if an unbalance exists. Zero volts on all three phases is considered a balanced condition. This allows the Model 2002Y to be used with shunt breakers, so that main power can be restored without resetting breakers.
The solid-state sensing circuit drives an internal electromechanical relay. Indicator lights on the monitor show when the voltage balance is within an acceptable range; when an unbalance exists; and when the relay is actually tripped.