The Siemens SIRIUS 3RH1122-1WB40 is a coupling relay for switching auxiliary circuits — the kind of part that sits between a PLC output or pushbutton and the coil of a larger contactor, or that drives signal lamps, solenoid valves, and interlock loops in a control panel. It is not a motor-load contactor; its job is signal-level switching in the auxiliary circuit, not main power. The coil is rated 24 V DC with a pick-up threshold of 0.85 x rated value and a drop-out of 0.1 x rated value, and it draws a steady 1.4 W holding power — a fixed DC magnet, so no AC hum and no inrush spike beyond the initial pull-in. The built-in varistor across the coil suppresses the inductive kickback, which matters when a PLC or safety relay drives it: without that suppression the back-EMF can couple noise into the 24 V bus or damage the output driver. Contacts are 2 NO instantaneous (no delayed, lagging, or make-before-break variants), rated 10 A at 24 V, 6 A at 230 V, and derating to 1 A at 690 V.
Mounting and wiring in the panel
Size S00 footprint — 45 mm wide, 57.5 mm tall, 72 mm deep — and the fastening method is screw or snap-on onto a DIN rail. Terminals accept solid conductors: 2x 0.5 to 1.5 mm², 2x 0.75 to 2.5 mm², and 2x 4 mm². The dual-wire entry per clamp is useful for daisy-chaining the common rail without extra terminals — a time-saver on repetitive auxiliary circuits.