What it is and what it does
The Siemens 3RH2122-1FB40 is a SIRIUS auxiliary contactor, size S00, designed to switch control and signal circuits in motor starter and contactor assemblies. It carries 2 NO instantaneous contacts rated for 10 A at 24 V and 230 V, with a 24 VDC coil that draws 4 W closing power. The built-in diode surge suppressor handles the inductive kick from the DC coil, so you don't need an external flyback diode across the coil terminals.
Mounting and panel fit
This contactor mounts via screw or snap-on onto 35 mm DIN rail, per the standard EN 60715 profile. The 45 mm width and 73 mm depth fit the S00 footprint, which is the smallest in the SIRIUS contactor family. Mounting position allows ±180° rotation on a vertical surface and ±22.5° tilt forward/backward, so you can orient it to match existing wiring ducts. Clearance around the arcing zone: 10 mm upward, 10 mm forward, 10 mm downward, 6 mm to the side — these are the minimum free-air gaps for arc extinction at rated switching.
Contact ratings and switching capability
The 2 NO contacts are rated for AC-15 and DC-13 control-circuit duty. At 24 V they switch 10 A; at 230 V the same 10 A holds. For higher voltages the current derates: 4.7 A at 60 V, 3 A at 110 V, 1.2 A at 220 V, 3 A at 400 V, 0.5 A at 440 V, 2 A at 500 V, 0.26 A at 600 V, and 1 A at 690 V. The mechanical life is 30 million operations; the electrical life at rated AC load is 10,000 operations per hour. Arcing time runs 10 to 15 ms, and the DC switching time (including bounce) is 38 to 65 ms.
Environmental and compliance
Operating temperature range is -25 to +60 °C; storage range is -55 to +80 °C. The unit is rated for pollution degree 3 (conductive pollution or dry non-conductive that becomes conductive due to condensation) and relative humidity from 10% up to condensation. RoHS compliance date is 2009-10-01 per the substance prohibition date. The product extension auxiliary switch is available as an add-on, and the design uses a diode surge suppressor across the coil.