What it is and where it fits
The Siemens SIRIUS 3RH2122-1KG40-0LA4 is an auxiliary contactor in the size S00 frame, designed for switching control and signal circuits rather than motor loads directly. It provides 2 normally-open and 2 normally-closed instantaneous contacts, rated for DC switching up to 125 V with a built-in suppressor diode across the coil. Mounts via screw or snap-on onto a 35 mm standard mounting rail, with a 45 mm width that fits two units per standard DIN-rail spacing. The mounting position allows ±180° rotation and ±22.5° tilt on a vertical surface, giving panel builders flexibility in tight enclosures.
Contact ratings — what they mean for your circuit
The contacts are rated for DC-13 duty (solenoid loads) at several voltage points: 10 A at 24 V, 4.7 A at 60 V, 3 A at 110 V, 1.2 A at 220 V, and 0.26 A at 600 V. For AC loads, the contacts handle 10 A at 230 V, 3 A at 400 V, and 1 A at 690 V. These are not motor-load ratings — they govern control-circuit switching of contactor coils, relays, and pilot devices. Mechanical life is rated at 30 million operating cycles, with a maximum switching frequency of 10,000 operations per hour at AC. Arcing time runs 10 to 15 ms, and the minimum off-time for DC loads is 7 to 20 ms.
Integration notes
The 45 mm width and size S00 footprint mean it occupies a single 45 mm DIN-rail slot, leaving space alongside a matching contactor or other S00 devices. Wiring accepts 2x 0.5–1.5 mm², 2x 0.75–2.5 mm², or 2x 4 mm² solid or stranded conductors. Clearance distances: 10 mm upwards, 10 mm forwards, 10 mm downwards, 6 mm to the side. The built-in suppressor diode eliminates the need for an external free-wheel diode across the coil, simplifying panel wiring.