Auxiliary contactor for control-circuit switching
The Siemens 3RH2122-2AP00 is a SIRIUS auxiliary contactor in size S00, carrying 2 normally-open instantaneous contacts.
The 2 NO contacts are rated for 10 A at 24 V and 230 V AC (50/60 Hz), but the continuous current drops significantly at higher voltages: 3 A at 400 V, 1.2 A at 220 V DC, and 0.26 A at 600 V DC. This derating curve means the part is primarily a control-circuit device for 24 V or 230 V AC pilot duty — not a power-switching contactor. The instantaneous contact design means no intentional delay — the contacts close and open with the coil state. For the coil, the operating range is 0.8 to 1.1 times rated voltage at 50 Hz and 0.85 to 1.1 at 60 Hz, giving a 20% undervoltage tolerance at 50 Hz that helps ride through brief sags without dropping out.