What it is and what it fits
The Siemens 3RH2911-2NF22 is a front-mounted auxiliary switch block for the SIRIUS 3RT2 contactor family and 3RH2 contactor relays. It provides two normally-open and two normally-closed contacts, with two of the NC contacts designated as solid-state compatible — meaning they are rated for reliable switching at low-level signals (5 V, 1 mA) where standard contacts might oxidize and fail to conduct. The note on the order code — "with 3RT2.2/3/4" — confirms it mounts directly onto the front of 3RT2 contactors in frame sizes S2, S3, and S4, as well as the corresponding 3RH2 contactor relays. No adapter plate or wiring harness needed; it snaps on.
Key ratings and what they mean for the panel
Rated insulation voltage is 690 V at pollution degree 3, which is the standard for industrial control panels where conductive dust or condensation may be present. Surge voltage resistance is 6 kV, matching the impulse withstand of most IEC 60947-4-1 motor starter circuits. The auxiliary contacts are rated for 0.3 A at both 24 V and 60 V — this is the continuous thermal current (Ith) for the contact path. For motor control circuits drawing 0.1–0.2 A per contact (PLC inputs, relay coils), this leaves headroom. The mechanical life is 5 million operating cycles, typical for a snap-on auxiliary block in a contactor that itself may see 1–2 million cycles before replacement. Contact reliability is specified as one incorrect switching operation per 100 million at 5 V, 1 mA. That is the figure that matters when the block is used with solid-state inputs or low-power PLC cards — standard contacts can fail to close at those levels. The two NC contacts marked as solid-state compatible are the ones that meet this spec.
Mounting and wiring
Snap-on mounting onto the contactor front face — no DIN rail space consumed. The block measures 36 mm wide by 47.7 mm deep by 41.5 mm high, so it adds minimal projection beyond the contactor envelope. Spring-loaded terminals accept 2 x 0.5 to 2.5 mm² without ferrules, or 2 x 0.5 to 1.5 mm² with ferrules. AWG equivalents are 2 x 20 to 14. No screw torque to verify — consistent with panel-builder preference for spring-cage terminations on auxiliary wiring. IP20 protection on the front face means it is finger-safe but not washdown-rated; suitable for enclosed panels, not for direct spray zones.