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.
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.
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.