What it is and what it does
The Siemens SIRIUS 3RT1024-3BW44 is a Size S0 power contactor rated for motor switching duty. It handles 7.5 kW at both 500 V and 690 V, with an AC-2 rating of 5.5 kW at 400 V and an AC-4 rating of 12.5 A at 400 V. That means it's built for squirrel-cage motors where the starting current is moderate (AC-2) or for reversing/inching duty where the contactor breaks full-load current (AC-4). The magnet coil draws 5.4 W for both closing and holding, so the coil suppression circuit sees a steady load. Operating temperature spans -25 to +60 °C, and the front face carries IP20 protection — fine for a closed panel, but not for washdown areas.
Mounting and wiring
Mounts via screw or snap-on onto a 35 mm DIN rail per EN 50022. The 45 mm width and 85 mm height fit the S0 footprint; side-by-side mounting is allowed with a 6 mm gap at the side for heat dissipation. Main circuit connections use screw-type terminals accepting 2x (0.25 to 2.5 mm²) solid or 2x (1 to 6 mm²) stranded, up to 10 mm² max. AWG equivalents are 2x (16 to 12) solid and 2x (14 to 10) stranded. For short-circuit coordination, Type 1 requires a 63 A gL/gG fuse; Type 2 requires a 25 A gL/gG fuse. That's a key spec for panel builders — Type 2 keeps the contactor usable after a fault, Type 1 lets it be sacrificial.