The Siemens 3RH2911-4HA21 is a SIRIUS auxiliary switch block designed to snap onto the front of contactors in sizes S00, S0, S2, and S3. It provides two normally open (N/O) instantaneous contacts, with no normally closed (N/C) or delayed contacts on this variant. The connection method is ring terminal lug, which means you'll need to crimp ring terminals onto your control wiring — no cage clamps or screw terminals here. The part is rated for AC-12 operational current up to 10 A and carries a mechanical service life of 10,000,000 operating cycles typical.
Snap-on front mounting means this block clips directly onto the contactor's front face without tools. The footprint is 36 mm wide, 37.5 mm high, and 43.7 mm deep.
Mirror contact and safety circuit use
This auxiliary switch is listed as a mirror contact per IEC 60947-4-1 when used with 3RT2 contactors. That means the N/C contact position is mechanically linked to the main contact position — critical for safety circuits where you need to positively confirm the main contacts are open before allowing access or enabling a bypass. If your safety application requires mirror contacts, verify the mating contactor is a 3RT2 series.
For BOM freeze or compliance documentation needs, the manufacturer provides standard SIRIUS-series declarations. This order code is the exact variant with ring terminal lugs and 2 N/O contacts — confirm your panel wiring practice accepts ring terminals before substituting a different terminal-style variant.