The Siemens 3RK1325-6LS41-3AA3 is a SIRIUS reversing starter — a motor starter that can change rotation direction without an external contactor interlock. It's designed for reversing loads like conveyors, hoists, and pumps where forward/reverse cycling is part of normal operation. Rated at 5.5 kW at 400 V (7.5 hp at 460/480 V, 10 hp at 575/600 V), it handles common three-phase motor sizes in a compact IP65 enclosure — meaning it's sealed against dust and low-pressure water jets, so it can sit directly on the machine frame or near the motor, not just inside a panel.
Trip class is selectable between CLASS 5, 10, 15, and 20. That's the maximum time in seconds the overload relay allows before tripping at 7.2× full-load current. Class 10 is the default for standard motor starting; drop to Class 5 for fast-cycling or high-inertia loads that need tighter thermal protection, or go to Class 15/20 for hard-starting applications like crushers or compressors. Supply voltage is 24 V DC nominal (20.4 to 28.8 V operating range), with a maximum permissible of 31.6 V. That's the control voltage for the internal logic and AS-Interface communication — not the motor power circuit. The motor power comes through the HAN Q4/2 connector on the main circuit side. Four digital inputs are available for local control signals — enough for start, stop, forward, and reverse commands without an external I/O block. Addressing is via an M12 plug, which is standard for fieldbus nodes in distributed installations. On-delay is 85 ms, off-delay 65 ms — fast enough for most sequencing but not for safety-rated stop categories; if you need SIL/PL-rated off-delays, the internal timer isn't the path. Shock resistance is 12g at 11 ms, vibration resistance 7 mm / 2g, so it holds up on machine-mounted applications near rotating equipment.
Where and how to mount it
Mounting position is flexible — vertical, horizontal, or flat — but horizontal is recommended for best heat dissipation from the overload relay. Fastening is by screw fixing; no DIN-rail clip on this unit, so plan for four screws into a backplate or machine frame. IP65 means the enclosure is dust-tight and protected against water jets from any direction — suitable for washdown areas in food processing, outdoor installations under a canopy, or dusty environments like sawmills. The degree of pollution rating is 3, so it's designed for conductive or dry non-conductive pollution typical of industrial floors.
That covers most plant-floor environments without derating; if your ambient regularly exceeds 55 °C, you'll need to consider a different enclosure or forced cooling.