The Siemens 3RN1012-1BB00 is a thermistor motor protection evaluation unit from the SIRIUS 3RN1 series. It monitors motor winding temperature via PTC thermistors and trips the control circuit when the motor overheats, preventing winding damage. The unit provides two CO (changeover) contacts for auxiliary signaling — one for the alarm/trip, the other for a fault indication or remote reset. That covers standard panel voltages across regions without needing a separate power supply variant. The screw-type terminals are straightforward for panel wiring, and the 22.5 mm width fits a standard single-module DIN-rail slot — no extra space needed.
The reclosing lockout function prevents automatic restart after a trip — important for motor protection where manual reset is required by code or safety procedure. If your application needs auto-reset, the successor 3RN2012-1BA30 has a selectable mode for that.