What it is and where it fits
The Siemens SIRIUS 3RH1911-1LA20-ZX95 is an auxiliary switch block that adds two normally-open (2 NO) contacts to a size S00 contactor or contactor relay. It snaps onto the front of the contactor — no tools, no extra wiring space — and connects via screw terminals sized for 2x (0.5…1.5 mm²) or 2x (0.75…2.5 mm²) conductors. Rated at 10 A at 24 V and 6 A at 230 V for AC-15 duty, it handles the typical pilot-duty loads — relay coils, contactor coils, indicator lamps — that a control panel throws at auxiliary contacts. The contacts are rated for a mechanical life of 10 million switching cycles and achieve a contact reliability of one incorrect switching per 100 million operations at 17 V, 5 mA. The block is IP20 front-protected, sized 36.5 mm wide by 37.5 mm high by 41.5 mm deep, and mounts on a 35 mm DIN rail via the contactor's own snap-on feature. Operating temperature range is -25 to +60 °C.
Lifecycle reality — phased out, successor ready
For new designs or replacement of a failed unit, the 3RH2 series (e.g., 3RH2122-1WB40) offers the same 2 NO contact arrangement, similar AC-15 ratings (10 A at 24 V, 3 A at 400 V), and adds a varistor surge suppressor. The 3RH2 also supports screw and snap-on mounting onto 35 mm DIN rail, but the larger depth may conflict with shallow enclosures.