What it is and where it lands
The Siemens 3RT1025-1BW44-1AA0 is a SIRIUS power contactor in the S0 frame size — the middle footprint of the three SIRIUS contactor frames, sized for motor loads up to 11 kW at 690 V AC-3. It mounts on a 35 mm DIN rail per EN 50022, screw or snap-on, and takes up 45 mm of rail width. Screw-type terminals on both main and auxiliary circuits; the front face carries IP20 protection, the terminal area is IP00 — meaning the panel builder needs to keep live parts behind a door or cover.
What the ratings mean for fit
The headline motor rating is 11 kW at 690 V AC-3 and 10 kW at 500 V AC-3. AC-3 is the standard duty for squirrel-cage induction motors — starting, running, and plugging. The AC-4 rating at 400 V is 15.5 A, which covers inching and reversing duty where the contactor makes and breaks stalled-rotor current. For resistive loads (AC-1) the thermal current is 10 A. The short-circuit coordination figures tell you what upstream fuse to spec: Type 2 coordination requires a 25 A gL/gG fuse; Type 1 coordination allows a 63 A gL/gG fuse. Type 2 means the contactor remains usable after a fault; Type 1 means it may need replacement but the fault is cleared.
Wiring and environment
Main circuit terminals accept 2x (0.5…1.5 mm²), 2x (0.75…2.5 mm²), and up to 2x (0.75…4 mm²) solid, or 2x (1…2.5 mm²), 2x (2.5…6 mm²), and up to 2x 10 mm² stranded. AWG equivalents are 2x (16…12), 2x (14…10), and 1x 8. The coil holds at 48 V DC with a closing and holding power of 5.4 W DC. Operating temperature range is -25 to +60 °C. Side-by-side mounting is allowed with a 6 mm gap at the side — no derating penalty for packing contactors tight on the rail, but the panel builder should check the thermal curve above 40 °C.