What it is and what it does
The Siemens 3RH1921-1CA10-ZX95 is a SIRIUS auxiliary switch block — a single-pole normally-open contact that snaps onto the front of a size S0 contactor or contactor relay, adding one auxiliary circuit without extra wiring or panel space. Rated for 10 A continuous in AC-12 duty (resistive loads) and 6 A at 230 V, it handles typical control-circuit switching for contactor coils, pilot lights, and PLC inputs across a range of voltages: 6 A at 24 V, 2 A at 48/60 V, 1 A at 110 V, 0.9 A at 125 V, 0.3 A at 220/250 V, and 3 A at 400 V. The contact is a mirror contact per IEC 60947-4-1 when used with a 3RT1 contactor, meaning its NO position mechanically mirrors the main contactor poles — critical for safety circuits where a welded main contact must not be masked by a false auxiliary feedback.
Mounting and panel fit
Snaps onto the front of a size S0 contactor (3RT1 series) — no tools, no DIN-rail space consumed. Dimensions are 51 mm deep, 10 mm wide, 38 mm tall, so it adds negligible depth to the contactor body. Terminals accept 2 x (0.5…1.5 mm²) or 2 x (0.75…2.5 mm²) solid/stranded, or 2 x (20…16) / 2 x (18…14) AWG. Front protection is IP20 — fine inside an enclosure, not for washdown zones.
Reliability and compliance
Rated for 10 million mechanical operating cycles typical, with a contact reliability of one faulty switching per 100 million operations at 17 V, 1 mA — suitable for low-level signal switching without stiction. Surge voltage withstand is 6 kV. The part carries a substance prohibitance date of 07/01/2006, indicating RoHS compliance from that date.