What it is and what it does
The Siemens 3RH1131-2KF40 is a SIRIUS coupling relay designed for switching auxiliary circuits in control panels. It carries three instantaneous normally-open (NO) contacts and a 110 V DC coil. The size S00 footprint (45 mm wide, 60 mm tall, 73 mm deep) fits standard DIN-rail enclosures alongside contactors of the same frame class. The coil draws 2.3 W for both closing and holding, so the thermal load on the control transformer is predictable — no inrush spike to size for. A built-in varistor suppresses the switching surge across the coil, which extends the life of downstream PLC outputs driving it. Rated for pollution degree 3, this relay handles the conductive-dust and humidity conditions typical of industrial control cabinets without conformal coating. The IP20 front protection means it's safe for finger access in enclosed panels but not for washdown areas.
Switching capacity — what the ratings mean for your circuit
The contact ratings are given per voltage, not as a single blanket ampacity. At 24 V it switches 10 A; at 110 V it switches 1 A; at 230 V it switches 6 A; at 400 V it switches 3 A; at 500 V it switches 2 A; at 690 V it switches 1 A. These are thermal current ratings (Ith) for AC loads — the actual make/break capability for inductive DC loads will be lower. For a 110 V DC control circuit, the 1 A rating is the hard limit; don't assume the 10 A at 24 V carries over. Contact reliability is specified as one incorrect switching operation per 100 million cycles at 17 V, 1 mA. That's the low-energy switching floor — if your circuit runs dry contacts at logic levels, this relay will hold up. The mechanical life of the contactor typical is 30 million operations, so the electrical endurance at rated load will be the limiting factor in high-cycle applications.
Mounting and integration
Mounts via screw or snap-on onto 35 mm DIN rail. The mounting position allows +/-180° rotation on a vertical surface and +/-22.5° tilt forward/backward, so it fits in tight swing-panel layouts. Wire termination accepts 2x (0.25 to 2.5 mm²) solid or stranded conductors — no ferrule required for solid wire, but stranded should use ferrules for reliable cage-clamp grip. Shock resistance is rated at 10g for 5 ms and 5g for 10 ms, which covers most industrial vibration environments short of direct hammer-mill mounting. The storage and transport temperature range of -55 to +80 °C exceeds the operating range of -25 to +60 °C — the relay can sit in an unheated warehouse or truck without issue.