Digitally Adjustable Line Monitor for Phase and Voltage Integrity
The Siemens 3UG5618-2CR21 is a digitally adjustable monitoring relay covering phase failure, phase sequence, asymmetry, frequency, and over- and under-voltage on three-phase supplies from 90 to 690 V AC at 15–70 Hz. Two changeover contacts with spring-loaded terminals give you a clean break for control logic, and the SIL 1/PL c rating means it slots into safety-related signal paths without a separate safety relay for basic fault detection.
The 90–690 V AC input range covers standard low-voltage motor feeds (400 V, 480 V, 575 V) without a separate PT. Phase asymmetry detection is adjustable, letting you set the trip threshold to match motor sensitivity—tight for critical spindles, looser for general pump duty. The phase sequence correction feature means the relay can swap its own internal logic to maintain correct output signaling even if the incoming phase rotation is reversed, saving a panel rewire.