CM-SRS.21S Current Monitor for Overload and Phase Loss
The ABB 1SVR730840R0400 is a CM-SRS.21S current monitoring relay in the ABB CM family, used to detect overcurrent, undercurrent, and phase loss conditions on three-phase motor loads. It sits in the Phase & Voltage Loss Monitors subcategory, meaning it's wired into the control circuit of a motor starter or contactor to trip on fault conditions — a common fit in compressor, pump, and conveyor panels where unmonitored single-phasing would burn out a winding.
The CM-SRS.21S uses screw-clamp terminals; the current transformer input passes through the relay body, and the output contacts are rated for switching the coil of a contactor or PLC input module.