The Siemens 3RN1012-2CK00 is a thermistor motor protection evaluation unit from the SIRIUS 3RN1 series. It monitors PTC thermistor sensors embedded in motor windings and trips the contactor when the winding temperature exceeds the threshold, protecting against overload or cooling failure. The unit operates on 230 V AC at 50 or 60 Hz and provides one normally-open and one normally-closed auxiliary contact (1 NO + 1 NC) for control and alarm signaling.
The 3RN1012-2CK00 is marked as 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 the same contact configuration (1 NO + 1 NC) at 230/110 V AC. For new designs or line-down replacements, the 3RN2012-2BW30 is the direct drop-in replacement.
Rated for 230 V AC at both 50 and 60 Hz, this unit is a straight swap in panels using standard European line voltage. The 1 NO + 1 NC contact arrangement covers the basic motor protection scheme: the NO contact drops the contactor coil on over-temperature, and the NC contact signals the fault to a PLC or alarm lamp.
The 22.5 mm width matches the standard single-module DIN-rail footprint, so it fits into any 35 mm rail panel without crowding adjacent devices. Screw and snap-on mounting lets you either fasten it with a screw or clip it directly onto the rail — handy when retrofitting into an existing panel where the rail is already populated.