A microcontroller-based universal 3-phase voltage band monitor for protecting 3-phase motors of any size from abnormal power conditions. The Model 22VB can detect under voltage, over voltage, voltage unbalance, reverse phase, and single-phasing even when regenerated voltage is present. Status of the 3-phase system is indicated by LEDs .

Relay operation is fail-safe, i.e. the two SPDT output contacts drop out when a fault condition or loss of power occurs. Under and over voltage trip points are both adjustable. The under voltage adjustment has two scales, 185-240VAC and 370-480VAC. The over voltage adjustment also has two scales, 208-264VAC and 416-528VAC. The Model 22VB will auto-range to the appropriate scale. Trip and restart delay adjustments are provided to preventing nuisance tripping during power fluctuations or short cycling in compressor applications. Voltage unbalance trip point is fixed at 6%.

The Model 22VB does not require a neutral connection and can be used on either Wye or Delta systems. Operating power for the Model 22VB is drawn from phases A and C.