SIRIUS S0 power contactor, 24 V DC coil
The Siemens 3RT1025-1BB40-ZX95 is a SIRIUS power contactor in the Size S0 frame, designed for switching motor loads and resistive circuits in industrial control panels. It mounts via screw or snap-on onto a 35 mm DIN rail per DIN EN 50022, fitting a 45 mm wide footprint on the rail. The magnet coil is rated 24 V DC, drawing 5.4 W for both closing and holding, so the coil supply can be a standard 24 V DC power supply without inrush oversizing. The contactor switches up to 10 A at 24 V for DC loads, and at 400 V AC-4 duty it handles 15.5 A — that's the rating for reversing or plugging applications where the contacts make and break under load. For three-phase motor starting, the contactor is rated 10 kW at 500 V and 11 kW at 690 V, covering common 400 V and 690 V line supplies. The IP20 front enclosure protects against finger contact, while the terminals themselves are IP00 — expect to mount this inside a cabinet with a door or cover.
Termination and wiring
Main circuit connections use screw-type terminals. Solid conductors: 2x (0.5 to 1.5 mm²), 2x (0.75 to 2.5 mm²), max 2x (0.75 to 4 mm²). Stranded: 2x (1 to 2.5 mm²), 2x (2.5 to 6 mm²), max 2x 10 mm². AWG equivalents: 2x (16 to 12), 2x (14 to 10), 1x 8. That covers most panel wiring up to 10 mm² without needing ferrule adapters. Side-by-side mounting is allowed with 6 mm spacing at the side, keeping the panel fill factor predictable. The contactor is rated for operation from -25 to +60 °C and up to 2000 m altitude without derating.
Coordination and protection
For Type 1 coordination (no damage to the contactor but it may need replacement after a fault), use a gL/gG fuse rated up to 63 A. For Type 2 coordination (contactor remains operational after a fault), limit the fuse to 25 A gL/gG. That's the standard selectivity guidance for this frame size.