What this SIMATIC reversing starter is
The Siemens 3RK1304-5LS70-3AA3 is a reversing motor starter in the SIMATIC family — a fully enclosed, fieldbus-connected unit rated for 12 A at 400 V AC and carrying a 100 kA breaking capacity at that voltage. It's designed to reverse a three-phase motor on command, not just start and stop it; the reversing contactor pair is built in, so you get forward and reverse switching without external interlocks.
Key ratings and what they mean for fit
The 12 A rating at 400 V AC is the continuous motor current it can handle in AC-3 duty — that's the real selection number, not a thermal or resistive rating. It drives a motor up to roughly 5.5 kW at 400 V. The 100 kA breaking capacity at 400 V means the starter can safely interrupt a fault current up to that level without welding contacts or venting plasma; that's important for SCCR compliance downstream of a high-capacity feeder. Trip class is adjustable across CLASS 5, 10, 20, and 30, so you can dial in the overload curve to match the motor's starting profile — class 10 for a pump, class 20 for a high-inertia fan. The IP65 enclosure seals the electronics and contacts against hose-directed water and dust ingress — this unit lives on the machine, not inside a clean control cabinet. Mounting is via screw fixing in either vertical or horizontal orientation, with dimensions of 230 mm high, 110 mm wide, and 160 mm deep. The power connection uses a socket per ISO23570, a standardized M12-style interface for the main infeed.
Fieldbus and I/O integration
This starter speaks both PROFIBUS DP and PROFINET — it's not just a motor switch, it's a distributed I/O device on the network. It provides 4 digital inputs via M12 sockets, giving you local sensor feedback without a separate remote I/O block. The I/O image uses 2 bytes of input data and 2 bytes of output data. Supply voltage is 24 V DC nominal, with a permissible range of 20.4 to 28.8 V.