The Siemens 3RH1921-1FE31 is a SIRIUS auxiliary switch block designed for mounting on 3RT1 contactor relays and power contactors. It provides three instantaneous contacts: two normally open (encapsulated) and one normally open plus one normally closed (not encapsulated). Snap-on mounting onto a DIN rail or directly onto the contactor makes it a straightforward addition to a panel build. Rated at 0.3 A at both 24 V and 60 V, this block handles low-current signaling and control loads common in auxiliary circuits. The screw-type terminals accept solid or stranded wire: 2x (0.5 to 1.5 mm²) and 2x (0.75 to 2.5 mm²), or AWG equivalents 2x (20 to 16) and 2x (18 to 14). Contact reliability is rated at one faulty switching per 100 million operations at 17 V, 1 mA — a solid figure for dry-circuit logic. The front face carries IP20 protection, suitable for enclosed panel environments. Insulation voltage is 690 V AC at pollution degree 3, with a surge voltage resistance of 6 kV. Operating temperature range is -25 to +60 °C; storage range is -55 to +80 °C. Mechanical service life is 5 million switching cycles typical.
Panel Integration
Snap-on mounting onto 35 mm DIN rail or directly onto the contactor. Dimensions: 44 mm wide, 38 mm high, 51 mm deep — fits within the standard S0 to S12 contactor envelope. No additional wiring harness or adapter needed; the screw terminals match the existing control-circuit wiring practice.