When a UVR is installed in a circuit breaker does it provide complete 3-phase under-voltage protection?
No it does not. A UVR is a single-phase device and provides only basic under-voltage protection. The UL489 requirements are: (a) the UVR must NOT drop out at 70% or higher applied voltage (b) it must drop out at 35% or lower voltage (c) the coil must pick up at 85% voltage. The UVR must be energized before the circuit breaker can be closed. The requirement for full under-voltage protection generally means, 3 Phase sensing and acting to trip the circuit breaker at about 70 to 80% voltage. An external relay must be provided for this type of protection.
