ABB CM-SRS.21 Over Under Current RMS Monitoring Relay 220-240V

ABB CM-SRS.21S Over and Under Current RMS Monitoring Relay is a true RMS measuring device for single-phase circuits that triggers control signals when the monitored current falls outside preset limits, delivering reliable overcurrent and undercurrent protection. It runs on 220–240 V AC (50/60 Hz), belongs to ABB’s CM-SRS family of measuring and monitoring relays, and provides two changeover contacts (2 c/o) for signaling and interlock purposes. The current-sense range is 3 mA to 1 A RMS, enabling accurate monitoring across typical loads, and the tripping delay is configurable (0 s or 0.1–30 s) to suit different protection schemes. This relay uses a true RMS measuring principle to maintain accuracy even with non-sinusoidal waveforms and is designed for electrical distribution and machine-control applications where maintaining current within specified limits is critical. Two changeover contacts enable independent signaling or interlocks with other protection devices, aiding integration into standard control circuits.