What this SIRIUS S0 contactor is and where it fits
The Siemens 3RT1025-1BG40-1AA0 is a SIRIUS power contactor in the S0 frame size, rated 7.5 kW at 400 V in AC-2 duty and 15.5 A in AC-4. It mounts on a 35 mm DIN rail per EN 50022 or screws directly to a panel, with a 45 mm width that takes one standard module slot. IP20 on the front, IP00 at the terminals — meaning the wiring zone expects enclosure protection, but the front face is touch-safe for panel access.
Motor switching and coordination
AC-2 at 400 V gives you 7.5 kW — that's the rating for slip-ring motor starting, where the contactor makes and breaks at reduced current. AC-4 at 400 V is 15.5 A, covering plugging and inching duty on standard squirrel-cage motors. For type 2 coordination, the upstream fuse is 25 A gL/gG; for type 1, 63 A gL/gG. That's the difference between a welded contactor (type 1) and one that stays operational after a fault (type 2).
Coil and auxiliary circuit
The magnet coil draws 5.4 W on both pick-up and hold — a DC-operated coil that doesn't spike on closure. Auxiliary contact ratings: 10 A at 24 V, 6 A at 230 V, 3 A at 400 V, 0.3 A at 220 V DC. That covers most PLC output cards and relay interfaces without an intermediate slave relay.
Terminal capacity and wiring
Main circuit terminals accept screw-type connections: 2x (1 to 2.5 mm²) solid, 2x (2.5 to 6 mm²) stranded, or a single 10 mm². The auxiliary/control circuit terminals take 2x (0.5 to 1.5 mm²) or 2x (0.75 to 2.5 mm²), max 2x 4 mm². AWG equivalents: main 2x (16 to 12), 2x (14 to 10), or 1x 8; control 2x (20 to 16), 2x (18 to 14), max 2x (18 to 12). Strip and torque per the terminal markings — no special tooling needed.