The Siemens 3UG5512-2AR21 is a line monitoring relay from the SIRIUS family, purpose-built for three-phase networks. It detects phase failure, incorrect phase sequence, and asymmetry across a supply range of 3x 160-690 V AC at 15-70 Hz, outputting a single changeover contact via spring-loaded terminals. The SIL 1/PL c rating means it can be used in basic safety-related control circuits up to Performance Level c per ISO 13849-1.
The 160-690 V AC operating range covers standard low-voltage motor supplies (400 V, 480 V, 575 V) without needing a separate voltage tap. Spring-loaded terminals accept 0.2-2.5 mm² conductors — no screwdriver needed for wiring, which speeds panel assembly. The single changeover contact (1 CO) is enough to signal a PLC digital input or drop out a contactor coil; if you need two isolated signals, you'll need an auxiliary relay.