What it is and what the ratings mean for fit
The Siemens 3RH2122-1BG40-Z W97 is a SIRIUS contactor relay with a 125 V DC coil, 2 normally-open and 2 normally-closed main contacts, and screw terminals in frame size S00. The 125 V DC coil voltage is the critical fit parameter — it determines whether this relay picks up and seals in your DC control circuit. The 2 NO + 2 NC contact arrangement gives you two independent form-A and two form-B contact sets for interlocking, auxiliary switching, or logic feedback in a motor starter or control scheme. Frame size S00 is the smallest in the SIRIUS contactor family, meaning the relay occupies minimal DIN-rail space in the panel — roughly 45 mm wide per unit. The screw terminals accept solid or stranded copper up to 2.5 mm², per the standard S00 terminal spec. Multi-unit packaging (40 pieces per pack) is intended for OEM builds or scheduled panel production, not single-unit replacement.
Lifecycle and sourcing reality
The active status means no last-time-buy pressure. The part is quoted to order against an RFQ; confirm the 125 V DC coil variant matches your control voltage before specifying.
Where it is used
This contactor relay is used in motor control centers, panel builder assemblies, and industrial automation cabinets where a DC-operated auxiliary relay is needed for contactor coil switching, PLC output interposing, or signal isolation. The S00 frame size snaps onto standard 35 mm DIN rail per EN 60715, and the screw terminals simplify field wiring without special tooling.