What this SIRIUS reversing starter is and what it does
The Siemens 3RK1325-6LS71-3AA5 is a SIRIUS reversing motor starter — a self-contained unit that combines a reversing contactor pair, overload protection, and an AS-Interface communication interface in one IP65 enclosure. It is designed for direct-on-line reversing of three-phase motors up to 5.5 kW at 400 V (7.5 hp at 460/480 V), with selectable trip classes 5, 10, 15, or 20 to match the motor's thermal time constant. The 24 V DC control supply (20.4–28.8 V range) powers the onboard electronics and the AS-Interface link, which handles both I/O data and parameterization through a single M12 connection. The IP65 rating means the enclosure is dust-tight and protected against low-pressure water jets — suitable for washdown zones in food processing, automotive assembly, or packaging lines where a central cabinet is impractical. Mounting is via screw fixing; the unit can be installed vertically, horizontally, or flat, though horizontal is recommended for optimal heat dissipation.
Key ratings and what they mean for fit
The 5.5 kW rating at 400 V AC-3 (motor starting) defines the maximum three-phase induction motor this starter can handle under normal duty. The selectable trip class (5, 10, 15, or 20) lets you match the overload relay's thermal curve to the motor — Class 10 for standard squirrel-cage motors, Class 20 for high-inertia loads like fans or centrifuges. The 4 digital inputs (24 V DC, M12-connected) can be used for local pushbuttons or sensor feedback, reducing the need for a separate I/O block. The reversing function is built in — no external interlocking required. ON-delay of 25 ms and OFF-delay of 35 ms are fixed, ensuring a dead time between forward and reverse that prevents phase-to-phase shorting. The unit also supports reverse starting directly, with no additional contactor.
Integration into a panel or line
Dimensions are 294 mm wide × 215 mm high × 159 mm deep. The screw-fixing method and multiple mounting positions (vertical, horizontal, flat) give flexibility for enclosure layout, but horizontal mounting is recommended for thermal performance. The main circuit connects via a HAN Q4/2 plug (per ISO 23570); the AS-Interface and digital inputs use M12 connectors. The IP65 enclosure allows direct mounting on the machine frame, eliminating a separate control cabinet.