What it is and what it does
The Siemens 3RH1122-1BD40 is a SIRIUS auxiliary contactor in the compact S00 frame size, designed to switch control-circuit loads — think PLC digital outputs driving relays, contactor coils, or indicator lamps in a panel. Its 42 V DC coil pulls in at the rated voltage and holds at 3.2 W, typical for a 24–48 V DC control bus. The contact block carries 2 normally-open and 2 normally-closed instantaneous contacts, rated 10 A in AC-12 duty (resistive loads at up to 690 V). For DC switching, the 24 V rated current is 10 A, dropping to 1 A at 110 V and 0.27 A at 220 V — a curve that reflects the arc-quenching limits of a 4-contact block.
Mounting and integration
Mounts via screw or snap-on onto a DIN rail — the 45 mm width and 57.5 mm height fit the standard S00 footprint, with zero side clearance required. The mounting position allows ±180° rotation on a vertical surface and ±22.5° tilt forward/backward, so it fits tight enclosures. Terminal capacity accepts solid conductors up to 4 mm² or stranded with ferrule, covering typical control wiring from 0.5 to 2.5 mm². Front face is IP20 — safe for finger-probe access inside a closed panel.