What it is and what it does
The Siemens SIRIUS 3RH1131-2MB40-0KT0 is a coupling relay for switching auxiliary circuits, part of the SIRIUS family. It provides 3 normally open instantaneous contacts, each rated for 10 A at AC-12 duty with a 24 VDC coil. This is a size S00 device, meaning it fits the smallest frame in the SIRIUS contactor range — useful for control panels where space is tight and you only need auxiliary switching, not main power. Mounting is flexible: screw fixing or snap-on onto a DIN rail, with a mounting position that allows +/-180° rotation on a vertical surface and +/-22.5° tilt forward/backward. This gives panel builders options when laying out a dense cabinet.
Key ratings and what they mean for fit
The 24 VDC coil draws 1.4 W for both closing and holding power — a steady-state load that matters when sizing a 24 VDC power supply for a multi-relay panel. At 1.4 W per relay, a string of ten adds 14 W to the supply budget. Contact ratings span the common control voltages: 10 A at 24 V, 6 A at 230 V, 3 A at 400 V, 2 A at 500 V, and 1 A at 690 V. The AC-12 rating (10 A) covers resistive and solid-state loads typical in auxiliary circuits — not motor starting. Surge voltage resistance is rated at 6 kV, which means it can handle transient overvoltages common in industrial environments without flashover. This is a key spec for panels near VFDs or welding equipment. The front face carries an IP20 rating — protected against finger contact but not water ingress. This is standard for panel-mounted control gear; keep it inside an enclosure rated for the environment. Operating temperature range is -25 to +60 °C, with storage and transport from -55 to +80 °C. The shock resistance of 10g for 5 ms and 5g for 10 ms covers most industrial vibration profiles without needing additional damping.
Wiring and integration
Terminals accept solid conductors from 0.25 to 2.5 mm² — standard for control wiring. The depth of 73 mm, width of 45 mm, and height of 60 mm mean it occupies about the same footprint as a typical ice-cube relay but with higher mechanical endurance (30 million operations typical). Side clearances are 0 mm, so relays can be mounted side-by-side without spacing — useful when packing multiple units on a DIN rail. Pollution degree 3 means it's rated for conductive pollution typical in industrial panels. Maximum operating altitude is 2,000 m without derating. Above that, you'd need to account for reduced dielectric strength in thinner air.
Sourcing and lifecycle
If you're cross-referencing against a panel originally built around a 3RT1015 series contactor, note that the 3RH1131 is a dedicated auxiliary contactor — it lacks main power contacts. It's designed to be driven by a PLC output or a larger contactor's auxiliary circuit, not to switch motor loads directly.