What it is and what it does
The Siemens 3RN1012-2BM00 is a thermistor motor protection evaluation unit from the SIRIUS 3RN1 series, designed to monitor motor winding temperature via PTC thermistors and trip the contactor when the motor overheats. It operates on a 230 V AC supply at both 50 and 60 Hz, and includes a reclosing lockout function that prevents automatic restart after a fault — important for applications where a manual reset is required for safety.
Key ratings and what they mean for fit
At 22.5 mm wide, this unit snaps onto a standard DIN rail (screw and snap-on mounting) and occupies one slot in a control panel — the same footprint as a typical miniature circuit breaker or slim relay. The spring-loaded terminals (cage-clamp style) accept solid or ferruled stranded conductors up to 2.5 mm², so no screwdriver torque is needed; just strip 8–10 mm and push in. IP20 means it's protected against solid objects larger than 12.5 mm (fingers) but not against moisture — mount it inside a closed panel.
Lifecycle and sourcing reality
The 3RN1012-2BM00 is a phased-out product. The preferred successor is the 3RN2012-2BW30, which offers the same thermistor motor protection function with manual/auto/remote selection and 2 W power consumption. For existing installations or BOM lines that require the exact 3RN1012-2BM00, we source it through our supply network — submit an RFQ for current availability and pricing. No spare, no sleep: if you're holding a critical spare for a legacy motor starter, this is the one to keep in the cabinet.
Where it's used
This evaluation unit is part of the motor feeder protection chain in industrial control panels — typically paired with a contactor and overload relay to protect motors against overtemperature caused by overload, blocked rotor, or cooling failure. The reclosing lockout ensures that after a thermal trip, the motor cannot restart until the fault is acknowledged, which is standard for conveyors, pumps, and compressors in process lines.