What it fits and what the contacts handle
The Siemens 3RH2911-1NF20 is a front-mounted auxiliary switch block for the SIRIUS contactor family, specifically designed for the 3RT2.2, 3RT2.3, and 3RT2.4 sizes as well as 3RH2 contactor relays. It provides two normally open (NO) contacts rated for solid-state loads — meaning they switch cleanly at the low-voltage, low-current levels typical of PLC inputs and electronic modules, not just the higher currents of conventional pilot-duty circuits. Contact reliability is specified as one incorrect switching operation per 100 million operations at 5 V, 1 mA, so it's trustworthy for direct wiring to a 24 VDC digital input card without an interposing relay. Rated insulation voltage is 690 V AC at pollution degree 3, and surge voltage resistance is 6 kV — standard for industrial control panels where the auxiliary circuit shares the same cabinet as motor feeders.
Mechanical and environmental limits
The block snaps onto the contactor front via the standard SIRIUS clip — no tools needed, and it occupies 36 mm width, 37.5 mm height, and 43.7 mm depth, staying within the contactor's own envelope. Operating temperature range is -25 to +60 °C; storage range is -55 to +80 °C, covering most indoor panel environments. IP20 on the front means finger-safe but not sealed — fine for a clean, dry enclosure; not for washdown areas.
Wiring and lifecycle
Screw-type terminals accept 2x (0.5 to 1.5 mm²) or 2x (0.75 to 2.5 mm²) with core-end processing, or the AWG equivalents — standard for panel wiring with ferruled stranded conductors. Mechanical service life is 5 million operating cycles typical, which is the contactor's own mechanical endurance — the block won't wear out before the base unit.