The Siemens SIRIUS 3RH1921-1CA01-ZX95 is a front-side auxiliary switch block carrying one normally-closed (NC) contact, terminated with screw-type terminals, and designed to snap onto 3RT1 contactors and contactor relays. Its 10 mm width and 51 mm depth fit the standard SIRIUS footprint, so it mounts flush alongside the contactor without stealing extra DIN-rail space.
The contact is rated 10 A maximum, but the real-world switching capacity depends on voltage and duty. At 24 V it handles 10 A (resistive) or 6 A (AC-15 inductive); at 230 V it still carries 6 A, dropping to 3 A at 400 V. The AC-15 rating at 690 V is 1 A — that governs the inductive load curve for contactor coils and small solenoid valves at higher voltages. For DC switching, the 24 V rating is 6 A, 110 V drops to 1 A, and 220 V to 0.3 A. The 6 kV surge voltage resistance and 690 V rated insulation voltage (pollution degree 3) mean this block is rated for the same panel voltage class as the 3RT1 contactor it mounts on.
Panel integration
Snap-on mounting to the 3RT1 contactor — no DIN rail required for the switch itself, though the contactor occupies the DIN rail. The 10 mm width means a full auxiliary block stack (up to four blocks) adds only 40 mm to the contactor's width. Screw 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 front protection is standard for the panel interior.