The Siemens 3RK1325-6KS41-0AA5 is a SIRIUS direct motor starter — a self-contained unit that combines a contactor, overload relay, and AS-Interface communication in one IP65 enclosure. It's designed for decentralized motor control right at the machine, not back in a central panel. The AS-Interface protocol onboard means it talks directly to the fieldbus without a separate gateway module, saving a slot and a wiring step. Four digital inputs are integrated for local sensors or pushbuttons, so you can handle start/stop and feedback without pulling extra I/O cable.
The trip class is selectable between CLASS 5, 10, 15, and 20. That's the overload curve — CLASS 10 for standard motor starts, CLASS 20 for high-inertia loads like fans or centrifuges where the start takes longer. Pick the class that matches your motor's acceleration time; setting it too fast nuisance-trips, too slow risks winding damage. The unit is rated for direct-on-line starting only — no reversing, so if you need forward/reverse, this isn't the one. Motor power ratings: 0.75 kW at 400 V, 750 W at 500 V, 0.7 hp at 460/480 V, 1 hp at 575/600 V. That puts it in the fractional-to-small motor range — pumps, small conveyors, agitators.
Power and environment
Supply voltage is 24 VDC nominal, with a range of 20.4 to 28.8 V. Minimum permissible is 26.5 V, maximum 31.6 V — so a sagging 24 V bus below about 20 V will drop the starter out. The IP65 rating means it's dust-tight and protected against hose-directed water — fine for washdown areas, food processing, or outdoor installs under a cover. Shock resistance is 12g for 11 ms, vibration resistance 7 mm / 2g — tough enough for most machine-mounted duty.
Mounting position is flexible — vertical, horizontal, or flat — but the recommended orientation is horizontal. Fastening is screw fixing, so you'll need a drill and M5 or M6 hardware; no DIN-rail clip on this one. Dimensions: 294 mm wide, 215 mm high, 159 mm deep. That's a substantial footprint — plan your subplate layout accordingly. The main circuit connects via a HAN Q4/2 plug per ISO 23570, and device addressing is through an M12 plug. Keep those connector types in mind when ordering mating halves.