The Siemens 3RH2122-2LV40 is a coupling contactor relay built for railway applications. It carries 2 normally-open and 2 normally-closed contacts, with a 36 V DC coil that picks up from 0.7 to 1.25 times the rated control supply voltage. A varistor is integrated across the coil to suppress switching transients — no external snubber needed on the DC side. The relay is housed in frame size S00 and terminated with spring-loaded terminals, so wiring is a push-in job, no screwdriver required.
What the Ratings Mean for Fit
The 36 V DC coil with a 0.7 to 1.25 times US operating range means the relay picks up reliably anywhere from about 25 V to 45 V DC — important if your DC bus sags under load or floats high on a floating battery bank. The integrated varistor clamps inductive kickback at the source, which keeps the EMI off the rest of the control loop. Spring-loaded terminals accept 0.2 to 2.5 mm² solid or ferruled stranded wire; strip length is 8 mm. Frame size S00 snaps onto a standard DIN rail, so it fits right into a railway control cabinet alongside other S00 contactors and relays.