The Siemens 3RH2122-2LB40-1AA0 is a SIRIUS coupling relay — a size S00 contactor-style relay for switching auxiliary circuits in control panels. The 24 VDC coil draws 2.8 W closing power, and a built-in varistor handles surge suppression — no external snubber needed for most PLC or relay logic outputs.
Rated at 10 A at both 24 V and 230 V, this relay handles typical auxiliary loads — contactor coils, indicator lamps, solenoid valves — across common control voltages. At 60 V it carries 4.7 A, at 110 V it carries 3 A, and at 400 V it carries 3 A. The 690 V rating drops to 1 A, which still covers most pilot-duty circuits in 690 V panels.
The relay measures 45 mm wide, 70 mm high, and 116 mm deep — the depth matters when the panel door or gland plate is tight. These are the numbers to check if you are packing relays into a crowded enclosure.