What it is and what it fits
The Siemens 3RH1921-2FE22 is a SIRIUS auxiliary switch block designed to snap onto 3RT1 contactors and contactor relays. It provides one normally-open and one normally-closed instantaneous contact, wired through spring-loaded terminals that accept 2x (0.5... 1.5 mm²) with ferrule or 2x (0.5... 2.5 mm²) solid/stranded, plus 2x (20... 14) AWG. The front face carries IP20 protection, meaning it's safe for finger contact inside a panel but not for washdown environments.
Key ratings and what they mean for your panel
Rated at 0.3 A at both 24 V and 60 V, this switch is sized for low-current control signals — think PLC inputs, contactor coils, or indicator lamps. The contact reliability spec of 1 faulty switching per 100 million operations at 17 V, 1 mA confirms it's solid-state-compatible, meaning it won't bounce or fail to close on low-energy logic loads. Surge voltage resistance of 6 kV and an insulation voltage of 690 V at pollution degree 3 give it the clearance to sit on a 400 V contactor without tracking. Mechanical life is 5 million switching cycles typical, so in a conveyor line cycling once every 10 seconds it'll outlast the machine's overhaul interval.
Mounting and integration
Snap-on mounting onto the contactor's front face — no tools, no DIN rail. The block measures 44 mm wide, 38 mm high, and 51 mm deep, so it adds minimal depth to the contactor stack. Spring-loaded terminals mean no screw tightening; strip to 8 mm, push the wire in. Operating temperature range is -25 to +60 °C; storage from -55 to +80 °C.