SIRIUS auxiliary contactor for signal switching and control logic
The Siemens 3RH2122-1BM40 is a SIRIUS auxiliary contactor in size S00, designed to switch control signals, interlock circuits, and feedback loops in motor starter assemblies and PLC output slices. Its 2 NO instantaneous contacts handle rated operational currents from 10 A at 24 V and 230 V AC down to 0.26 A at 600 V AC, covering the voltage range typical of 24 VDC control buses and 230/400 VAC line-level signaling. The DC coil draws 4 W on pick-up and 4 W holding, a steady-state load that a 24 VDC power supply or PLC output card must budget for per contactor.
Ratings and what they mean for fit
The switching capacity table tells the real story: at 24 V rated value the contacts carry 10 A, at 230 V rated value also 10 A, but at 440 V rated value that drops to 0.5 A and at 600 V rated value to 0.26 A. This derating follows the arc-quenching limits of the S00 air gap — for a 480 V control circuit, verify the load current against the 440 V column. The mechanical life of 30,000,000 cycles is the theoretical limit; electrical life will be lower and depends on the switched load, but the figure confirms the contactor is rated for high-cycle applications like pick-and-place or packaging lines. Pollution degree 3 means the contactor is rated for conductive pollution environments typical of industrial control panels without conformal coating — normal for a DIN-rail enclosure in a factory floor cabinet. The operating temperature range of -25 to +60 °C covers most indoor installations; storage from -55 to +80 °C handles shipping and warehouse extremes.
Mounting and integration
Fastening method is screw and snap-on mounting onto 35 mm DIN rail. The S00 footprint — 45 mm wide, 57.5 mm tall, 73 mm deep — fits standard 45 mm slot spacing. Mounting position allows +/-180° rotation on a vertical surface and +/-22.5° tilt forward/backward, so the contactor can be oriented to suit wire routing. Clearance distances: 10 mm upwards, 10 mm forwards, 10 mm downwards, 6 mm at the side — maintain these to adjacent metalwork or grounded surfaces for arc flash and creepage compliance. Terminals accept 2x (0.5 to 1.5 mm²), 2x (0.75 to 2.5 mm²), or 2x 4 mm² solid or stranded copper. The product extension auxiliary switch is available, meaning additional contact blocks can be ganged onto this base unit without replacing the coil assembly.