What this part is and what it does
The Siemens SIRIUS 3RH1921-1FA22-ZW98 is an attachable auxiliary switch block designed to snap onto 3RT1 series power contactors and contactor relays. It adds four poles of auxiliary contacts — 2 normally open and 2 normally closed — to the base contactor, following the EN 50005 terminal numbering standard. The block mounts via snap-on fastening onto a 35 mm DIN rail alongside the contactor, occupying a 44 mm wide footprint. Rated for a maximum current of 10 A, the auxiliary contacts carry a range of switching capacities across different voltage levels: 6 A at 24 V, 6 A at 125 V, 6 A at 230 V, 6 A at 250 V, 3 A at 400 V, and 0.3 A at 220 V. The contacts are rated for AC-15 duty at 690 V at 1 A, which covers solenoid and electromagnetic load switching typical in control circuits. Mechanical service life is 10 million switching cycles typical, with a contact reliability of one faulty switching per 100 million operations at 17 V and 1 mA — suitable for PLC-level signal integrity.
Lifecycle and sourcing reality
This part is a phased-out product. The manufacturer lists it as current but with a clear successor: the SIRIUS 3RH2 series. The 3RH1921-1FA22-ZW98 is sold in multi-unit packaging of 40 pieces. For new designs or BOM lines that need a long-term supply commitment, the 3RH2 series is the official replacement path. Existing installations using 3RT1 contactors with this auxiliary block can continue to source the 3RH1921-1FA22-ZW98 through the surplus and broker channel — it is quoted to order against an RFQ, not stocked as a production-run item.
Integration and mounting
The block snaps onto the front of a 3RT1 contactor and also onto the DIN rail via the contactor's own mounting foot. Dimensions are 44 mm wide, 51 mm deep, and 38 mm high — it adds minimal depth to the contactor assembly. Screw-type terminals accept 2x (0.5 to 1.5 mm²) or 2x (0.75 to 2.5 mm²) with core-end processing, or 2x (20 to 16) and 2x (18 to 14) AWG. IP20 protection on the front means it is suitable for enclosed control panels where no washdown or dust ingress is expected. Operating temperature range is -25 to +60 °C; storage range is -55 to +80 °C. Surge voltage resistance is rated at 6 kV, with an insulation voltage of 690 V at pollution degree 3.