What this contactor is and where it lands
The Siemens 3RT1025-1AU00 is a SIRIUS S0 power contactor with three normally-open main contacts, screw-type terminals, and a 45 mm wide housing that snaps onto a 35 mm DIN rail per DIN EN 50022. It switches motor loads in control panels — the AC-2 rating of 7.5 kW at 400 V covers slip-ring motors, and the AC-4 rating of 15.5 A at 400 V handles reversing or inching duty where the contactor makes and breaks full load current. The 91 mm depth and 85 mm height fit standard enclosure backplates; side-by-side mounting is allowed with a 6 mm gap to adjacent devices for thermal clearance.
Ratings that decide the fit
The 24 V coil draws 10 A at rated voltage — that's the inrush for the solenoid, not the continuous hold current, so size the control transformer for the peak. Wire termination accepts solid or stranded: 2x (0.5…1.5 mm²) and 2x (0.75…2.5 mm²) for control wiring, and up to 2x 10 mm² or 1x 8 AWG for the main power circuit — enough for the motor leads this contactor typically serves. Rated operational current at AC-12 (control-circuit duty) is 10 A maximum; the auxiliary contact block you add must stay within that limit.
Mounting and integration
Snap-on mounting onto 35 mm DIN rail per EN 50022 — no tools needed for the rail, but the screw terminals need a screwdriver for the power and control connections. Front face is IP20, terminal area is IP00 — the contactor is intended for inside an enclosure, not exposed to washdown or dust. Pollution degree 3 means it's rated for industrial environments with conductive pollution or dry non-conductive pollution that becomes conductive due to condensation — typical for unsealed panels in factory floors.