The Siemens 3RH2122-2JB40 is a SIRIUS coupling relay — size S00 — designed to switch auxiliary circuits in control panels. It carries 2 instantaneous NO contacts rated 10 A at 24 V and 230 V, 3 A at 400 V, and 1 A at 690 V, so it handles mixed-voltage auxiliary loads from a single 24 VDC coil. The built-in diode surge suppressor clips the flyback spike on the coil, which keeps the DC supply clean and protects adjacent PLC outputs or safety relays.
The 45 mm width and 73 mm depth fit the S00 footprint — common in Siemens SIRIUS contactor assemblies. Mounting position is flexible: ±180° rotation on a vertical surface, plus ±22.5° tilt forward/backward.
Wiring and thermal limits
Terminals accept 2 x 0.5 to 4 mm² solid or stranded wire. Operating temperature range is -25 to +60 °C; storage range -55 to +80 °C. The 10 000 operations per hour at AC and 38–65 ms at DC switching frequency means it keeps up with fast-cycle auxiliary loads like valve position feedback or conveyor zone control.