What it is and what it does
The Siemens 3RH1131-2JB40 is a SIRIUS coupling relay designed for switching auxiliary circuits — think signal isolation between a PLC output and a contactor coil, or interposing between a safety relay and a motor starter. It is not a main power contactor; its job is switching control loads up to 10 A in AC-12 duty (resistive loads and solid-state outputs). The 24 VDC coil draws 2.3 W both on pickup and hold, which is useful to know for power supply budgeting in a panel with multiple relays.
Mounting and integration
Mounts via screw or snap-on onto a DIN rail — the size S00 footprint (45 mm wide, 60 mm tall, 73 mm deep) is the smallest SIRIUS contactor frame, so it packs tightly on a rail. The mounting position is flexible: ±180° rotation on a vertical surface, plus ±22.5° tilt forward/backward. Zero side clearance is required, meaning you can butt it against adjacent devices without derating. Screw terminals accept 2x 0.25 to 2.5 mm² solid or stranded wire.
Ratings and what they mean
The headline rating is 10 A at AC-12 (resistive loads and solid-state outputs). AC-12 is the category for switching resistive loads and optocoupler inputs — common in control panels. The relay also carries a 6 A rating at 230 V and 3 A at 400 V, so it handles a range of control voltages. The built-in diode surge suppressor across the coil means you don't need an external flyback diode for DC switching; just watch polarity. Three instantaneous NO contacts (no delayed or make-before-break) give you three isolated signal paths from one coil.