What it is and where it lands
The Siemens 3RH2122-1BM40-ZX95 is a Size S00 contactor relay with two instantaneous normally-open contacts, designed for screw and snap-on mounting onto 35 mm DIN rail inside a control panel. At 45 mm wide and 73 mm deep, it fits the standard S00 footprint — the same slot as the base contactor it extends. The product extension auxiliary switch flag confirms this is the add-on relay block, not the main contactor coil assembly — it mounts directly onto the contactor or stands alone on the DIN rail.
DC switching — what the ratings actually mean
DC ratings are voltage-dependent because DC arcs don't self-extinguish at zero-crossing. This relay carries 10 A at 24 V, drops to 4.7 A at 60 V, 3 A at 110 V, 1.2 A at 220 V, and bottoms out at 0.26 A at 600 V. The arcing time of 10 to 15 ms and DC operating frequency up to 1 000 1/h mean it handles frequent switching in DC control circuits — think PLC interposing relays or DC valve solenoids — but the load current must stay under the voltage-specific curve. At 400 V DC the rating is 3 A; at 690 V DC it drops to 1 A. If your circuit runs at an intermediate voltage, interpolate conservatively — the datasheet's discrete points are the only guaranteed values.
Mounting and clearances
Screw and snap-on onto 35 mm DIN rail. The mounting position allows +/-180° rotation on a vertical surface and +/-22.5° tilt forward/backward, so it fits odd panel orientations without derating. Clearance requirements: 10 mm upward, 10 mm forward, 10 mm downward, 6 mm at the sides. That's tight enough for dense S00 layouts — just watch the forward clearance if the panel door has components or wiring ducts. Terminal capacity accepts 2x 0.5 to 1.5 mm² solid/stranded, 2x 0.75 to 2.5 mm², or 2x 4 mm² — standard for control wiring up to 14 AWG.