The Siemens 3RH2122-2KF40-0LA0 is a SIRIUS auxiliary contactor in size S00, carrying 2 normally-open instantaneous contacts and a 110 VDC coil with an integrated suppressor diode.
The contact ratings are given at multiple voltage levels, and the right one to look at depends on your load voltage. At 24 V the contacts are rated 10 A, at 110 V it's 3 A, at 230 V it's 10 A, and at 400 V it's 3 A. These are thermal current ratings for the contact block — they tell you the continuous current the contacts can carry at that voltage level. For DC switching, the ratings drop significantly: 4.7 A at 60 V, 1.2 A at 220 V, 0.5 A at 440 V, and 0.26 A at 600 V. That steep derating curve is typical for DC because DC arcs are harder to extinguish than AC arcs. If you're switching a DC control circuit, size the load against the DC column, not the AC one.
Coil and Switching Dynamics
The 110 VDC coil draws 13 W closing power and includes a suppressor diode. Pickup voltage is 0.7 x rated; dropout is 1.25 x rated. Mechanical life is 30 million operations, switching frequency 10,000 1/h for AC, DC on-time 7 to 20 ms.
Mounting and Environmental Specs
Operating temperature range is -40 to +70 °C, storage is -55 to +80 °C, with 10% minimum relative humidity.