The 84873220 (H3US) is a three-phase monitoring relay designed to control overvoltage and undervoltage conditions between phases on 3-phase networks, with integrated phase failure detection. It features True RMS measurement with a measuring range of 194 to 528 V~ and operates on a rated control supply voltage of 3 × 220 to 3 × 480 V AC. The relay provides two changeover outputs rated at 6 A each, with adjustable voltage thresholds ranging from -2 to -20% for undervoltage and +2 to +20% for overvoltage, plus independent time delays from 0.3 to 30 seconds. In the event of phase failure, both relay outputs open instantaneously without waiting for the time delay, and LED status indicators display the fault condition. This relay is ideal for protecting industrial equipment and systems on 3-phase networks by preventing damage from voltage anomalies and phase loss conditions.