SIRIUS coupling relay for auxiliary circuit switching
The Siemens 3RH1122-2VB40 is a SIRIUS coupling relay designed for switching auxiliary circuits in control panels. It carries 2 normally open instantaneous contacts and is rated for 10 A at AC-12 duty, which covers resistive and lightly inductive loads typical in PLC output isolation or signal-level switching. The 24 VDC coil draws a constant 1.4 W for both closing and holding, so the power supply budget is predictable — no inrush spike to size around.
Mounting and integration
Mounts via screw or snap-on onto a DIN rail, with zero side clearance required, so you can pack it tight against adjacent devices in a crowded panel. The size S00 footprint (45 mm wide, 60 mm high, 73 mm deep) is the standard compact relay-contactor format for this class. Mounting position is flexible: +/-180° rotation on a vertical surface, plus +/-22.5° tilt forward/backward, which helps when routing wires in tight enclosures.
Environmental and electrical ratings
Operates from -25 to +60 °C and stores from -55 to +80 °C, with a maximum altitude of 2 000 m. Pollution degree 3 means it's rated for conductive pollution environments — typical for industrial control panels without climate control. The front face is IP20, so finger-safe but not sealed against moisture. Shock resistance is 10g / 5 ms and 5g / 10 ms, adequate for machine-mounted applications with moderate vibration.
Contact ratings and switching capability
The contacts are rated for switching at multiple 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 at 10 A is the headline figure for resistive loads. Mechanical service life is 30 million operations typical, so it's built for high-cycle applications like conveyor interlocking or machine-tool sequences. The built-in diode surge suppressor across the coil means you don't need an external flyback diode for DC switching — just verify polarity matches the circuit.
Wiring and termination
Terminals accept solid conductors from 0.25 to 2.5 mm², which covers standard control wiring up to 14 AWG. The screw terminals are straightforward for panel builders — no special tooling needed beyond a standard screwdriver.