What it is and what it does
The Siemens SIRIUS 3RH1122-1JB40 is a coupling relay designed for switching auxiliary circuits in control panels. It carries a 24 V DC coil with a closing and holding power of 2.3 W, and is rated for 10 A at 24 V in AC-12 duty, meaning it handles resistive and lightly inductive loads in control circuits. Two instantaneous NO contacts give you the basic switching paths for interlocking, signaling, or pilot duty.
Mounting and integration
This relay mounts via screw or snap-on onto a DIN rail, fitting the standard S00 contactor footprint — 45 mm wide, 57.5 mm high, 72 mm deep. Zero side clearance is required, so you can pack it tight against adjacent devices without derating. The mounting position allows +/-180° rotation on a vertical surface and +/-22.5° tilt forward/backward, giving flexibility in crowded enclosures. Pollution degree 3 means it's rated for industrial environments with conductive pollution.
Key ratings and what they mean
The AC-12 rating of 10 A at 24 V is the headline figure for control-circuit switching — it's the maximum continuous current for resistive loads like relay coils or indicator lamps. For higher voltages, the current derates: 6 A at 230 V, 3 A at 400 V, 1 A at 690 V. The coil's 2.3 W holding power is low enough to keep heat down in a sealed panel. The built-in surge suppressor with a diode protects the coil driver from flyback voltage — essential when the relay is driven by a PLC output or solid-state switch. Operating temperature range is -25 to +60 °C, with storage down to -55 °C. Shock resistance of 10g for 5 ms and 5g for 10 ms covers most vibration in industrial machinery.
Wiring and termination
The screw terminals accept solid conductors: 2x 0.5 to 1.5 mm², 2x 0.75 to 2.5 mm², or 2x 4 mm². This covers standard control wiring from signal-level up to 4 mm² for short power runs. The IP20 rating on the front means finger-safe when installed in a closed panel, but not protected against moisture — keep it dry.