S0 auxiliary switch for contactor front-mount
The Siemens SIRIUS 3RH1921-1CA10-ZW95 is an auxiliary switch block designed for snap-on mounting to the front of S0-size contactor relays and power contactors. It carries one normally open instantaneous contact and is rated as a mirror contact per IEC 60947-4-1 when used with 3RT1 contactors — meaning the NO position mechanically mirrors the main contact state, critical for safety circuits that need positive feedback of contactor weld or dropout. The switch block measures 10 mm wide, 51 mm deep, and 38 mm high, fitting the standard S0 footprint without consuming extra DIN rail space. Snap it onto the contactor front, wire the terminals — 2x (0.5…1.5 mm²) solid or 2x (0.75…2.5 mm²) stranded, or 2x (20…16) AWG / 2x (18…14) AWG — and it's live. IP20 on the front face keeps fingers out but expects enclosure protection beyond that.
AC-15 / DC-13 load ratings — what they mean for your circuit
The auxiliary contact is rated for AC-15 (solenoid/contactor coil) and DC-13 (electromagnet) loads at multiple voltages. At 230 V AC, it switches 6 A; at 400 V AC, 3 A; at 690 V AC, 1 A. For DC circuits, it handles 10 A at 24 V, 4.7 A at 60 V, 1.2 A at 220 V, and 0.26 A at 600 V. These are the operational currents — match them to your coil inrush or holding load, not the main contactor's motor current. Contact reliability is specified at 1 faulty switching per 100 million operations at 17 V, 1 mA — relevant for PLC-level dry circuits where oxide films on silver contacts can cause intermittent opens. Mechanical life is 10 million operating cycles typical.
Compliance and approvals
The switch carries a surge voltage resistance of 6 kV. Substance prohibitance date is July 1, 2006, indicating RoHS compliance from that point. It is designed as a mirror contact per IEC 60947-4-1, which implies the manufacturer has submitted it to the relevant type tests under that standard.