The Siemens 3RH2911-2NF02 is a front-mounted auxiliary switch block for the SIRIUS 3RT2 contactor and 3RH2 contactor relay family. It provides two normally-closed (NC) contacts, both rated for solid-state compatibility — meaning the contacts are designed for low-energy switching where oxide film on standard silver contacts can cause intermittent opens. The spring-loaded terminals accept 2x (0.5... 1.5 mm²) with ferrule or 2x (0.5... 2.5 mm²) solid, which matches the typical control-circuit wiring in a panel. Rated insulation voltage is 690 V at pollution degree 3, and surge voltage resistance is 6 kV, so it fits into 400/480 VAC control circuits without derating concerns.
The 'solid-state compatible' designation is the defining feature here. Standard auxiliary contacts rely on a minimum wetting current to punch through silver-oxide film — typically around 10-20 mA at 5-10 V. The 3RH2911-2NF02 is specified for one incorrect switching operation per 100 million operations at 5 V, 1 mA, which is two orders of magnitude lower than standard contacts. If your PLC input card or solid-state relay expects a dry signal at milliamps, this block prevents false opens. The two NC contacts are arranged as two separate current paths — labeled.1/.2 and.1/.2 in the description — so you can wire one to the safety circuit and one to the PLC feedback without sharing a common terminal.
Panel-fit notes
The block is 36 mm wide, 41.5 mm high, and 47.7 mm deep — front-mounted so it clips onto the contactor without adding depth behind the panel. Protection class IP20 on the front means it is finger-safe once installed; no additional cover required in a standard IP54 enclosure. The spring-loaded terminals release with a screwdriver push, which speeds up wiring changes during commissioning.