What it is and where it fits
The Siemens 3RH1122-2KF40 is a SIRIUS coupling relay designed for switching auxiliary circuits in control panels. It's a size S00 contactor relay, meaning it shares the same compact footprint as the S00 contactor family — 45 mm wide, 60 mm tall, 73 mm deep — so it slots into the same DIN-rail layout without stealing extra panel real estate. Mounts via screw or snap-on onto a DIN rail, and the mounting position is flexible: ±180° rotation on a vertical surface, plus ±22.5° tilt forward/backward. That's a lot of freedom for tight enclosures where you're working around existing wiring.
What the ratings mean for your circuit
The coil is rated 110 V — that's the pull-in and hold voltage. Closing power is 2.3 W DC, and holding power is the same 2.3 W DC, so the coil doesn't waste extra energy once it's sealed. A varistor is built in for surge suppression, which saves you from adding an external snubber on the coil. Contact ratings are given at multiple voltages, which tells you the switching capacity across common control 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. At 110 V — the coil voltage — the contact rating is 1 A. These are thermal current ratings for the auxiliary contacts; the actual making/breaking capacity depends on your load type (resistive vs. inductive), but these numbers give you the thermal limit. The relay carries 2 normally-open and 2 normally-closed instantaneous contacts — no delayed, lagging, or make-before-break options on this variant. Contact reliability is specified as one incorrect switching operation per 100 million cycles at 17 V, 1 mA, which covers dry-circuit (low-energy) switching where oxide films can cause trouble.
Environmental and compliance
IP20 on the front — that's finger-safe but not washdown-rated, so keep it inside a closed panel. Operating temperature range is -25 to +60 °C; storage and transport range is -55 to +80 °C. Pollution degree 3 means it's suited for industrial environments with conductive pollution (condensation, dust). Shock resistance is 10g / 5 ms and 5g / 10 ms — fine for most industrial machinery but not extreme shock applications. Substance prohibitance date is July 1, 2006 — that's the RoHS compliance cutoff. The part is designed to meet RoHS requirements for substances like lead, mercury, and cadmium.
Wiring and termination
Terminals accept solid wire from 0.25 mm² up to 2.5 mm², two conductors per terminal. That covers standard control wiring (1.5 mm² is typical for 24 V DC circuits). The screw terminals are standard for the SIRIUS family — no special tooling needed.