The Siemens SIRIUS 3RT1025-1AN24 is a size S0 power contactor rated for motor switching at 7.5 kW at 400 V AC-3 (50/60 Hz) and 11 kW at 690 V. It mounts via screw or snap-on onto 35 mm DIN rail per DIN EN 50022, with a 45 mm width that fits standard panel fill factor — three units per 135 mm section. Front face carries IP20; the terminal area is IP00, so gland-plate clearance and finger-safe shrouding are on you. Operating ambient range is -25 to +60 °C, pollution degree 3, so it holds up in non-climate-controlled enclosures near drives or transformers. The coil draws 10 A at 24 V rated value for the instantaneous contact set — verify your 24 VDC supply can handle the inrush before committing the BOM line.
Mounting and wiring constraints
Screw-type terminals on both main and auxiliary/control circuits. Main contact wiring accepts 2x (0.5 to 1.5 mm²), 2x (0.75 to 2.5 mm²), or max 2x (0.75 to 4 mm²) solid or stranded; auxiliary side takes 2x (1 to 2.5 mm²) or max 2x 10 mm². AWG equivalents: main 2x (16 to 12), 2x (14 to 10), 1x 8. Side-by-side mounting is permitted — no derating gap required, but the 6 mm side clearance to adjacent components is the minimum for heat dissipation. Depth of 140 mm and height of 85 mm mean it clears most 200 mm deep enclosures, but check gland-plate protrusion if the contactor sits near the back wall. The S0 footprint is shared across the SIRIUS 3RT1 family, so a swap to a higher-rated sibling keeps the same DIN rail drilling.
Coordination and protection
Type 1 coordination requires a gL/gG fuse rated 63 A; Type 2 coordination calls for 25 A. That's the short-circuit protection the contactor needs to survive a fault without welding — spec the fuse downstream accordingly. The reference code per IEC 81346-2 is Q, which maps to power switching in the panel schematic. Mechanical life is typical 10 million operations; the AC-4 rating at 400 V is 15.5 A for heavy inching or plugging duty. If your application cycles under load frequently, the AC-4 figure is the one that governs contact wear, not the AC-3 motor rating.