A microcontroller-based universal 3-phase voltage band monitor for protecting 3-phase motors of any size from abnormal power conditions. The Model 20VB 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. The Model 20VB is UL Recognized in the U.S. and Canada.

Relay operation is fail-safe, i.e. the 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 20VB will auto-range to the appropriate scale. A trip delay adjustment for preventing nuisance tripping during power fluctuations and a restart delay adjustment for preventing short cycling in compressor applications have also been provided. Voltage unbalance trip point is fixed at 6%.

The Model 20VB does not require a neutral connection and can be used on either Wye or Delta systems. Operating power for the Model 20VB is drawn from phases A and B.