The Siemens SIRIUS 3RH1122-1KB40 is a coupling relay purpose-built for switching auxiliary circuits in control panels. Rated 24 V DC coil with a contact rating of 10 A at 24 V, it provides two normally-open and two normally-closed instantaneous contacts (no make-before-break or delayed switching). The size S00 footprint — 45 mm wide, 57.5 mm tall, 72 mm deep — fits standard DIN-rail enclosures with screw and snap-on fastening.
The 10 A at 24 V rating governs resistive switching at the coil voltage; for higher AC voltages the contact current derates sharply — 6 A at 230 V, 3 A at 400 V, 1 A at 690 V. That derating curve means the part is sized for control-level loads (pilot lights, contactor coils, PLC inputs), not power circuits. The 2.3 W DC holding power keeps heat dissipation low inside a crowded enclosure — no forced cooling needed for a single unit. The built-in varistor surge suppressor snubs the DC coil's flyback voltage — no external free-wheel diode needed. Contact reliability is rated at one incorrect operation per 100 million cycles at 17 V, 1 mA, which matters for low-energy signal switching where oxide films can block conduction.
Shock resistance is 10g for 5 ms and 5g for 10 ms, adequate for most industrial machinery but not heavy impact zones. The S00 contactor size is the smallest Siemens SIRIUS frame; it shares the same DIN footprint as the matching contactor 3RT2015, simplifying bus-bar and wiring planning.