What it is and where it fits
The Siemens SIRIUS 3RH2911-2NE21 is a front-mounted auxiliary switch block designed specifically for 3RT2.2/3/4 contactors and 3RH2 contactor relays. Its snap-on mounting clips directly onto the contactor front without tools, saving DIN-rail space compared to side-mount blocks.
Contact configuration and solid-state compatibility
The contact set is 2 NO + 1 NC, but with a critical distinction: one NO and one NC are designated solid-state compatible. That means those two contacts are rated for the low-energy switching typical of PLC outputs or solid-state relays — 5 V, 1 mA with a contact reliability of one incorrect switching per 100 million operations. The remaining NO contact handles standard pilot-duty loads. If you're mixing a PLC input with a conventional relay load on the same block, wire the low-level signal to the solid-state compatible pair.
Electrical ratings and panel integration
Rated insulation voltage is 690 V at pollution degree 3, with a surge voltage resistance of 6 kV — adequate for 400 V line-to-line industrial panels with clearance to 480 V systems. The spring-loaded terminals accept 2x (0.5 … 1.5 mm²) with ferrule or 2x (0.5 … 2.5 mm²) solid/stranded, matching the typical control-wire gauges in a motor control center. Operating temperature range is -25 to +60 °C; storage range -55 to +80 °C. Mechanical service life is 5 million operating cycles typical.