The Siemens 3RH2911-1NE22 is a SIRIUS auxiliary switch block designed to snap onto the front of 3RT2 contactors and 3RH2 contactor relays. It provides 2 normally-open and 2 normally-closed instantaneous contacts, with two of those contacts (1 NO and 1 NC) rated as solid-state compatible — meaning they handle the low-voltage, low-current switching typical of PLC inputs and electronic modules without the contact oxidation that standard auxiliary contacts can develop in that range. The other two contacts (1 NO, 1 NC) are standard auxiliary contacts for general signal feedback. This block fits contactor frame sizes S00, S0, S2, and S3, which covers the full SIRIUS range from the smallest 3RT2 contactors up to the larger 3RT2 power contactors. The screw-type terminals accept 2x (0.5...1.5 mm²) or 2x (0.75...2.5 mm²) solid/stranded wire, or 2x (20...16) / 2x (18...14) AWG. The front-mount design adds 43.7 mm depth, 36 mm width, and 37.5 mm height to the contactor assembly.
Snap-on front mounting means no DIN rail space is consumed — the switch clips directly onto the contactor's front face. This is the typical arrangement for adding auxiliary contacts to a contactor that already occupies a DIN-rail position. The IP20 protection rating on the front means the terminals are finger-safe once wired, suitable for enclosed panel environments. The insulation voltage is rated 690 V AC at pollution degree 3, with a 6 kV surge voltage withstand — consistent with the contactor's own insulation coordination.
Compared to the 3RH2122-1BA40 — a DIN-rail-mounted auxiliary contactor rather than a front-mount switch block — the 3RH2911-1NE22 is a more compact, contactor-specific add-on. The 3RH2122-1BA40 measures 73 mm deep x 45 mm wide, requires its own DIN rail slot, and carries 10 A rated operational current at AC-12. The 3RH2911-1NE22 clips onto the contactor's front, adding only 43.7 mm depth and 36 mm width, and its contacts are rated for the signal-level switching that electronic controls demand. For a panel already using 3RT2 contactors, the front-mount block saves one DIN-rail position per contactor. If you are replacing a 3RH2122-1BA40 in an existing panel, the 3RH2911-1NE22 will not drop in directly — it requires the contactor's front-mount interface and rewiring to the contactor's coil terminals.
The mirror contact feature per IEC 60947-4-1 (applicable when used with 3RT2.2/3/4 contactors) means the NC contacts are mechanically linked to the NO contacts so that an NC mirror contact cannot close if the NO main contacts are welded. This is a safety requirement in applications where the auxiliary contact provides feedback to a safety circuit about the contactor's state. Contact reliability is specified as one incorrect switching operation per 100 million switching operations at 5 V, 1 mA — important for direct PLC input sensing without an interposing relay.