Snap-on auxiliary switch for SIRIUS contactors
This is a Siemens SIRIUS auxiliary switch — order code 3RH2921-2HA22-0KT0 — designed to snap onto the front of SIRIUS contactors in sizes S00, S0, S2, and S3. It adds two instantaneous normally-open contacts to the contactor relay or power contactor assembly, giving you extra signal feedback or control logic without a separate relay block.
Current ratings across the voltage range
The thermal current rating is 10 A at 24 V, but the actual switching capacity depends on the circuit voltage. At 24 V it handles 6 A; at 48 V and 60 V it drops to 2 A; at 110 V it's 1 A; at 230 V it's 6 A again (note the AC-15 style curve); at 400 V it's 3 A. The rated operational current figures tell a similar story: 10 A at 24 V, 4.7 A at 60 V, 3 A at 110 V, 1.2 A at 220 V, 0.5 A at 440 V, and 0.26 A at 600 V. These numbers matter when you're sizing the auxiliary circuit — a 24 VDC pilot light pulls different current than a 400 VAC contactor coil.
Mirror contact and contact reliability
This auxiliary switch carries a mirror contact per IEC 60947-4-1 when used with 3RT2 contactors — meaning the normally-closed contact mechanically mirrors the main contact position, critical for safety circuits that need to verify the main contacts have opened. Contact reliability is specified at 1 faulty switching per 100 million operations at 17 V, 1 mA, which covers dry switching of PLC inputs without contact wetting.
Mounting and panel fit
Snap-on mounting to the contactor front — no tools, no DIN rail space consumed. The dimensions are 36 mm wide, 47.7 mm deep, and 41.5 mm high, so it adds about 48 mm to the contactor depth. The front face is IP20 rated, meaning finger-safe but not washdown. Surge voltage resistance is 6 kV, which covers most industrial control panel transient environments.