The Siemens SIRIUS 3RN2012-2BW31 is a thermistor motor protection relay from the 3RN2 family, designed to evaluate PTC thermistor sensors embedded in motor windings.
Rated supply voltage spans 24-240 V AC/DC. The relay accepts solid and stranded conductors from 20-12 AWG. Output contacts are rated 1 A at 24 V, 0.2 A at 125 V, and 0.2 A at 240 V. These are signal-level ratings for driving a PLC input or contactor coil, not motor-level switching. The 0.2 ms at 240 V entry likely refers to a switching frequency or pulse rating — treat the contacts as low-power signal outputs. The relay includes auto-reset and error memory functions, selectable via internal settings. Auto-reset allows the motor to restart automatically after a thermistor cools, useful for pumps or fans. Error memory latches the trip until manually reset, preferred for conveyors or mixers where unexpected restart is unsafe.