The Siemens 3RH2122-1BG40-Z X95 is a contactor relay from the SIRIUS family, built into the S00 frame size. It carries 2 normally-open and 2 normally-closed contacts, with a 125 V DC coil and screw terminals. This is the part you reach for when a control circuit needs a compact relay to switch pilot loads — signal lights, contactor coils, PLC outputs — on a 125 V DC bus. The S00 frame keeps panel density high; it snaps onto DIN rail alongside other SIRIUS gear.
The 125 V DC coil rating is the first gate: if your control voltage is 125 V DC, this relay pulls in cleanly; below that dropout threshold, it won't hold. The 2 NO + 2 NC contact arrangement means you get two isolated make contacts and two isolated break contacts in one package — enough to interlock a starter and signal back to the PLC without an auxiliary block. Screw terminals on the S00 frame accept wire up to the standard cross-section for this class. No spring-cage here — if your panel spec calls for screw-clamp terminations, this is the variant.
It is in standard production. RoHS compliance dates from October 2009; REACH candidate-list information is available per Article 33.
Panel integration
Frame size S00 clips onto 35 mm DIN rail. The 61.5 x 50.0 x 77.5 mm footprint leaves room for adjacent contactors or overloads in a motor-control row. No derating needed at standard panel ambient; just verify the 125 V DC supply is stiff enough for the inrush.