The Siemens 3RH1122-2KV40 is a SIRIUS coupling relay — a size S00 auxiliary contactor designed for switching auxiliary circuits in control panels. It's the part that sits between a PLC output or pushbutton and the loads it drives: signal lamps, contactor coils, solenoid valves, or smaller motorized actuators. The 36 V DC coil means it's fed from a 36 VDC control supply, common in older or specific industrial installations where 24 VDC isn't the standard. Mounting is straightforward: screw it down or snap it onto a DIN rail. The IP20 front protection means it's intended for enclosed cabinets where no one's poking tools into live terminals.
For inductive loads like contactor coils, derate significantly: at 230 V AC the rating drops to 6 A, at 400 V AC it's 3 A, and at 690 V AC it's 1 A. These are the AC-15 / DC-13 switching capacities for auxiliary contactors, and they govern whether this relay can break the inrush of the load it's driving. The contact reliability spec — one incorrect switching operation per 100 million at 17 V, 1 mA — tells you it handles dry switching (low-energy signals from a PLC or sensor) without needing a wetting current. That's critical when this relay passes a 24 VDC digital input signal; you won't get intermittent opens from contact oxidation. Built-in surge suppression via a varistor means the coil's back-EMF is clamped when de-energized. No separate flyback diode needed across the coil terminals, which saves a wiring step and reduces panel clutter. The coil draws 2.3 W DC both during pickup and hold — a constant load on the 36 VDC supply that you need to budget for. Rated surge voltage resistance at 6 kV and pollution degree 3 means it's designed for industrial environments where transient spikes from motor starts or nearby lightning are a reality. It'll hold up in a panel next to VFDs or contactors without nuisance failure.
RoHS compliance is confirmed with a substance prohibitance date of July 1, 2006 — it meets the EU RoHS directive. No REACH or UL listing is explicitly stated in the available records, but as a Siemens SIRIUS component it typically carries CE and UL/CSA marks. Verify the nameplate markings against your local code requirements when the part arrives. For procurement: this is a quoted-to-order line. Submit an RFQ with your quantity and target lead time. The 73 mm depth, 45 mm width, and 60 mm height mean it fits standard S00 contactor footprints — no panel layout surprises if you're replacing an existing S00 auxiliary contactor.