What it is and what it does
The Siemens SIRIUS 3RT1025-1BE84 is a size S0 power contactor rated for motor switching in AC-3 duty at 10 kW on a 500 V line and 11 kW at 690 V. For AC-2 applications — slip-ring motor starting — it handles 7.5 kW at 400 V. The AC-4 reversing/inching rating is 15.5 A at 400 V. This covers the common motor sizes for small pumps, fans, and conveyors in a 45 mm wide package. The coil draws 5.4 W DC both on pick-up and hold, so the control transformer and DC supply don't need to handle a surge — it's a constant-load coil. That simplifies sizing for a 24 VDC control bus.
Mounting and integration
Snaps onto a 35 mm DIN rail per EN 50022 and can be mounted side-by-side with no derating gap — useful when packing multiple contactors into a tight panel row. The S0 frame is 45 mm wide, 85 mm tall, and 150 mm deep, which fits standard enclosure backpan layouts. Screw terminals on both the main and auxiliary/control circuits; wire sizes for the mains accept up to 2x 10 mm² or 1x 8 AWG. Front face is IP20 — finger-safe for the panel interior. The terminal area is IP00, meaning the connection points are exposed and require the panel enclosure to provide the overall ingress protection. Pollution degree 3 rating means it's suited for industrial environments with conductive dust or occasional condensation, common in control cabinets near process areas.
Coordination and protection
For Type 2 coordination (no damage to the contactor after a short circuit), Siemens specifies a 25 A gL/gG fuse upstream. Type 1 coordination (contactor may need replacement after a fault) allows a 63 A gL/gG fuse. This gives the panel builder a clear choice: smaller fuse for higher uptime, larger fuse for simpler coordination with downstream motor protection. Mechanical life is rated at 10 million cycles typical, which for a contactor in a cycling application like a compressor or dosing pump translates to years of service before a planned replacement.