What it is and where it fits
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.
Mounting and panel integration
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.