The Siemens 3RN1012-2GB00 is a thermistor motor protection evaluation unit from the SIRIUS 3RN1 family, designed to monitor motor winding temperature via PTC thermistors.
The 24 V AC/DC supply is the control voltage for the internal electronics and relay coil — it must match your panel's control bus. The two CO contacts (no NC or NO contacts) are the only output; each CO can be wired as normally-open or normally-closed, giving flexibility for trip alarms or motor starter interlocks.
The 22.5 mm width matches standard single-module DIN-rail devices — it occupies one slot in a panel. Depth of 91 mm and height of 103 mm are within typical enclosure depth allowances.