Phase monitoring relay for 160–690 V AC lines
The Siemens 3UG4512-2BR20 is a SIRIUS phase monitoring relay that watches three-phase AC lines from 160 to 690 V at 50 or 60 Hz. It detects phase loss and incorrect phase sequence — the two most common supply faults that kill motors and drives — and drops its output contacts when the line condition goes out of spec. The relay has two changeover contacts rated 3 A at 250/400 V AC, enough to signal a PLC or drop out a contactor coil directly.
The 160–690 V AC range covers low-voltage networks from 208 V to 600 V class without needing a separate voltage variant — one SKU handles 230/400 V and 480/577 V supplies.