The Siemens 3UG5514-2BR20 is an analog adjustment monitoring relay that covers four fault conditions on a three-phase line: phase failure, phase sequence reversal, phase asymmetry, and under-voltage. It accepts a wide supply range of 3x 160-690 V AC at 15-70 Hz, making it suitable for 50/60 Hz industrial networks across standard low-voltage distributions. The two changeover contacts (2 CO) are rated for the control circuit, and the spring-loaded terminals speed wiring in panel builds — no screwdriver torque check needed.
The 160-690 V AC input range covers 208 V, 400 V, and 690 V three-phase systems without needing a separate supply transformer. Phase asymmetry detection is a fixed percentage threshold set by the analog dial — useful for catching a blown fuse or a single-phase motor load imbalance before the motor protection trips. The two changeover contacts are typically wired to the PLC digital input or to a shunt-trip coil on the main breaker.
The housing dimensions are 127 x 111 x 38 mm (L x W x H) — fits a standard DIN-rail footprint with room for adjacent relays or terminal blocks. The analog adjustment potentiometer is on the front face, so set the threshold before snapping the relay onto the rail if the adjacent device clearance is tight.