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. Mounting is via screw fixing; the unit can be installed vertically, horizontally, or flat, though horizontal is recommended for optimal heat dissipation.
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.