What it is and where it fits
The Siemens 3RH2911-1HA02 is a SIRIUS auxiliary switch designed to snap onto the front of contactor relays and power contactors in sizes S00, S0, S2, and S3. It adds isolated auxiliary contacts without increasing the contactor's panel footprint — the switch rides on the front face, not beside it. Rated AC-15 at 230 V for 6 A and at 400 V for 3 A, this switch handles typical control-circuit loads like PLC inputs, relay coils, and indicator lamps. The AC-1 resistive rating reaches 10 A at 24 V, covering heater or transformer circuits. The 3RH2911-1HA02 carries a mirror contact per IEC 60947-4-1 when paired with a 3RT2 contactor — meaning the normally-closed contact cannot close if the main contacts weld. That matters for safety circuits where you need positive break confirmation.
Ratings that decide the fit
The AC-15 switching current drops as voltage climbs: 6 A at 24 V, 6 A at 230 V, 3 A at 400 V, and 1 A at 690 V. That 690 V rating is the one to check if you're switching control transformers on a 690 V line — most auxiliary switches top out at 600 V. Contact reliability is spec'd at one faulty switching per 100 million operations at 17 V, 1 mA — dry-circuit performance that matters for low-energy PLC inputs where oxide films won't burn through. Surge voltage resistance is 6 kV. No external varistor needed for most industrial environments.
Mounting and wiring
Snaps onto the front of the contactor — no DIN rail space consumed. The 36 mm width and 43.7 mm depth keep it within the contactor envelope; height is 37.5 mm. Panel builders can pre-wire the switch before snapping it on, which speeds assembly. Terminals accept 2 x 0.5 to 1.5 mm² solid/stranded or 2 x 0.75 to 2.5 mm² with ferrules, or 2 x AWG 20-14. The spring-cage design (implied by the wire ranges) holds without retightening — set it and forget it. IP20 on the front means finger-safe when mounted in a closed panel. Operating temperature range is -25 to +60 °C; storage range extends to -55 to +80 °C.
Lifecycle and sourcing
RoHS compliance date is October 1, 2009, covering the EU RoHS directive. No REACH or UL listing is in the evidence, but the IEC 60947-4-1 mirror-contact claim implies the switch is designed to that standard.