What it is and what it does
The Siemens 3RH1911-1NF02 is a SIRIUS auxiliary switch block designed for use with contactor relays and power contactors in the size S00 frame. It provides two normally-closed (NC) instantaneous contacts wired through screw-type terminals, and snaps onto a 35 mm DIN rail per EN 50022. Rated insulation voltage is 690 V at pollution degree 3, with a surge voltage resistance of 6 kV. The front face carries IP20 protection, meaning it is finger-safe once installed inside an enclosure. Contact reliability is specified as one incorrect switching operation per 100 million cycles at 17 V and 5 mA — this matters when the block is used to switch low-level electronic signals (e.g., PLC inputs) where oxide films on dry contacts can cause intermittent faults. Mechanical service life is rated at 5 million switching cycles typical, which is the expected endurance before mechanical wear-out under no-load conditions.
Lifecycle and sourcing reality
For buyers with a BOM line locked to the 3RH1911-1NF02 order code, the part is sourced through surplus and broker channels against an RFQ. The successor 3RH2911-1NF02 is the recommended drop-in for new builds or panel retrofits.
Integration notes
The block measures 36.5 mm wide, 37.5 mm high, and 41.5 mm deep — compact enough to fit on a crowded DIN rail alongside the base contactor. Snap-on mounting onto a 35 mm rail per EN 50022 means no tools are needed for installation or removal. Screw terminals accept two conductors per clamp: 0.5 to 1.5 mm² or 0.75 to 2.5 mm² with core-end ferrules, or 20 to 16 AWG and 18 to 14 AWG solid/stranded. This covers most control-circuit wiring in panel builds. Operating temperature range is -25 to +60 °C; storage range is -55 to +80 °C. The block is rated for use in electronics applications, meaning it is optimized for low-energy switching where contact oxidation is a concern.