What it is and what it does
The Siemens 3RT1025-1HB40 is a SIRIUS power contactor in the S0 frame size, designed for switching motor loads and resistive loads in industrial control panels. It carries a 24 V DC coil with a holding power of 4.2 W, and its main contacts are rated for 7.5 kW at AC-2 duty at 400 V and 11 kW at AC-3 duty at 690 V. The contactor mounts via screw or snap-on onto 35 mm DIN rail per EN 50022, fitting into standard panel layouts.
Key ratings and what they mean for fit
The DC-13 rating at 24 V is 10 A — that's the inductive load switching capacity for solenoids and contactor coils, not resistive heating. For motor switching, the AC-3 rating at 400 V is 10 kW, and at 690 V it's 11 kW, so this contactor handles standard 3-phase induction motors up to about 15 HP at 400 V. The AC-4 rating at 400 V is 15.5 A, covering reversing or inching duty where the contactor makes and breaks stalled-rotor current. Type 1 coordination requires a 63 A gL/gG fuse upstream; Type 2 coordination needs a 25 A gL/gG fuse. That's the short-circuit protection the contactor needs to survive a fault without welding its contacts — pick the coordination level your panel design calls for.
Mounting and integration
The S0 frame is 45 mm wide, 85 mm tall, and 101 mm deep — compact enough for dense DIN-rail layouts. Side-by-side mounting is allowed with a 6 mm gap to the side for heat dissipation. Screw terminals on the main circuit accept up to 2x 10 mm² stranded or 1x 8 AWG. The control circuit terminals take 0.5 to 4 mm². Pollution degree 3 rating means it's suited for industrial environments with conductive dust or occasional condensation.