The Siemens 3RH2122-1BM40-ZW97 is a size S00 contactor relay from the SIRIUS family, fitted with two normally-open instantaneous contacts and a 24 VDC coil that draws 4 W both on closing and holding. The 73 mm depth and 45 mm width keep it compact inside a crowded enclosure, and the mounting position is flexible: you can rotate it ±180° on a vertical surface or tilt it ±22.5° forward and backward, which helps when routing wires around other gear.
The contacts are rated for DC switching across a range of voltages: 10 A at 24 V, 4.7 A at 60 V, 3 A at 110 V, 1.2 A at 220 V, and 0.5 A at 440 V. These numbers define the resistive load curve the relay can break without excessive arcing — the arcing time sits between 10 and 15 ms for AC and 7 to 13 ms for DC, so you need that clearance around the relay to avoid flashover to adjacent components. Clearances: 10 mm upwards, forwards, downwards; 6 mm at sides. Pollution degree 3. Surge voltage resistance rated at 6 kV. For DC-12 duty the maximum operating frequency is 1,000 operations per hour — the lower figure reflects the longer arc extinction time on DC.
Terminals accept solid or stranded conductors: 2 × (0.5 to 1.5 mm²), 2 × (0.75 to 2.5 mm²), or 2 × 4 mm². The product extension for auxiliary switches is supported — you can add more contact blocks on the side if the two built-in NO contacts aren't enough for your logic. Relative humidity minimum is 10%, so no special climate control is needed for typical panel environments.