The Model 2500 3-Phase Monitor is designed to continuously monitor 3-phase power lines for abnormal conditions. This device features solid-state voltage and phase-angle sensing circuits, which drive a SPDT electromechanical output relay.

When the correct voltage and phase sequence is applied to a specified Model 2500, the output relay will not energize. An under voltage, phase reversal, phase unbalance or phase loss condition will cause the output relay to energize, even if regenerated voltage is present. Complete power loss will not cause Model 2500 to trip. The 2501 version of this unit operates in fail-safe mode, and the contacts de-energize on a fault condition. A neutral connection is not required, allowing the Model 2500 or 2501 to be used with either Wye or Delta system configurations.