The Siemens SIRIUS 3RH2122-2KF40 is an S00-size coupling relay designed for switching auxiliary circuits in control panels. It carries two instantaneous normally-open contacts and a 110 V DC coil with an integrated suppressor diode, so no external flyback diode is needed across the coil terminals. Rated switching current varies by voltage: 10 A at 24 V and 230 V, 3 A at 110 V and 400 V, 1.2 A at 220 V, and derated further at higher voltages down to 0.26 A at 600 V. The AC-15 / DC-13 duty class governs these numbers — use the 230 V 10 A figure for typical pilot-duty lamp or contactor coil loads, and the 24 V 10 A for DC solenoid valves in the same panel. The S00 footprint (73 mm deep, 45 mm wide, 70 mm tall) matches the standard SIRIUS contactor grid, so it shares the same rail pitch as the 3RT2 contactor line. Clearance of 10 mm upwards and forwards, 6 mm at the side keeps heat rise manageable in a dense cabinet.
Integration Notes
The built-in suppressor diode clamps the DC coil flyback; no external snubber required.