The Siemens 3RN2012-1BW30 is a SIRIUS 3RN2 thermistor motor protection relay — the standard evaluation unit with ATEX approval, open-circuit and short-circuit detection in the sensor circuit, and non-volatile error memory. It accepts a rated supply of 24 to 240 V AC/DC (50/60 Hz) and mounts on a 35 mm DIN rail via screw or snap-on. The 22.5 mm wide housing fits standard control-panel density; the IP20 enclosure is suited for inside-cabinet installation.
The 22.5 mm width leaves room alongside contactors or overloads in a motor starter cell. Terminals accept solid or stranded wire: 1x 20–12 AWG or 2x 20–14 AWG solid. The relay has a manual/auto reset selectable (auto-RESET = Yes) and an external reset input, so it can be wired into a remote reset pushbutton without opening the panel. The LED display version gives local status of trip and supply.