What it is and where it fits
The Siemens 3RH1921-1XA22-0MA0 is a SIRIUS auxiliary switch designed to snap onto the front of S0-size contactors and contactor relays. It carries 2 normally-closed (NC) instantaneous contacts and is rated for AC-15 duty at 10 A at 230 V, with a surge voltage resistance of 6 kV. The snap-on fastening method means it mounts directly onto the contactor without tools, saving DIN-rail space and panel wiring time.
Key ratings and what they mean for the buyer
The AC-15 rating of 10 A at 230 V is the key switching capacity for solenoid and contactor coil loads — typical in control circuits. The 6 kV surge voltage resistance means it withstands transient overvoltages common in industrial panels without flashover. The mirror contact function per IEC 60947-4-1 (when paired with 3RT1 contactors) provides a positively driven NC contact that reflects the main contact position, critical for safety circuits where you need to detect welding or sticking of power contacts.
Integration notes
Snaps onto the front of any S0-size Siemens contactor or contactor relay (e.g., 3RT10 series). Dimensions are 44 mm wide, 38 mm high, 51 mm deep — it adds only 51 mm to the contactor depth. Wiring accepts 2x (0.5 to 1.5 mm²) solid or stranded, or 2x (0.75 to 2.5 mm²) with ferrules; AWG equivalents are 2x (20 to 16) and 2x (18 to 14). The IP20 front protection means it's safe for finger contact inside an enclosed panel but not for washdown environments.