The Siemens SIRIUS 3RH1921-1CA01-ZW97 is a front-side auxiliary switch block that adds one normally-closed (NC) contact to a 3RT1 contactor or contactor relay. It snaps onto the front of the contactor without extra tools or wiring changes — the contactor's own actuating mechanism drives the auxiliary contact. Rated at 10 A maximum (10 A at 24 V rated value, 6 A at 230 V, 3 A at 400 V), it handles typical control-circuit loads like PLC inputs, relay coils, and indicator lamps. The mechanical service life of 10 million switching cycles means this block outlasts most contactors it rides on.
Snap-on mounting onto the contactor front — no DIN rail needed for the switch itself. The block is 10 mm wide, 38 mm high, and 51 mm deep, so it adds negligible width to the contactor stack. Screw-type terminals accept 2x (0.5...1.5 mm²) or 2x (0.75...2.5 mm²) with core-end processing, or AWG 20–16 and 18–14. IP20 on the front face is standard for enclosed panels; keep the cabinet door closed for washdown areas.