What it is and what it does
The Siemens 3RT1025-3BW40 is a SIRIUS power contactor in the S0 frame size, designed for switching three-phase motor loads in industrial control panels. It mounts via screw or snap-on onto a 35 mm DIN rail per EN 50022, so it integrates directly into a standard panel layout. Rated for AC-3 duty at 10 kW on a 500 V supply and 11 kW at 690 V, this contactor handles the motor starting and running currents typical of pumps, fans, and compressors up to that power band. The AC-4 rating of 15.5 A at 400 V covers reversing or inching applications where the contactor makes and breaks the load under full current. The DC magnet coil draws 5.4 W to close and holds at the same 5.4 W, which means the coil driver sees a steady load without a power drop-off after pickup — a detail that matters when sizing the 24 VDC supply for a panel with multiple contactors.
Mounting and integration
The S0 frame occupies 45 mm width on the DIN rail, with a height of 85 mm and depth of 100 mm. Side-by-side mounting is permitted, so you can gang multiple contactors without spacing — useful when packing a dense motor control center. The IP20 front enclosure protects against finger contact; the terminals themselves are IP00, meaning the wiring compartment is open to the panel environment. Main circuit screw terminals accept solid or stranded wire: 2x (0.25 to 2.5 mm²) or 2x (2.5 to 6 mm²), with a maximum of 2x 10 mm². For AWG, that translates to 2x (16 to 12) or 2x (14 to 10), with a single 8 AWG as the max. The auxiliary contact block (not included with this base unit) uses 2x (0.25 to 2.5 mm²) solid. Rated for pollution degree 3 and operating ambient from -25 to +60 °C, the contactor suits industrial environments with conductive dust or condensation. Maximum installation altitude is 2 000 m without derating.
Coordination and protection
For Type 1 coordination (no damage to the contactor after a short circuit, but it may need replacement), the maximum fuse is gL/gG 63 A. For Type 2 coordination (contactor remains operational after a fault), use a gL/gG 25 A fuse. These values govern the upstream short-circuit protective device selection — a decision the panel builder must make before wiring. Mechanical life is rated at 10 000 000 operations typical, which for a contactor on a moderate-duty conveyor or pump running a few cycles per minute translates to years of service before mechanical wear becomes a concern.