Integrator's brief — reversing motor starter with fieldbus
The Siemens SIMATIC 3RK1304-5KS40-3AA3 is a reversing motor starter rated for CLASS 10 overload protection, switching 2 A at 400 V AC. It integrates both PROFINET and PROFIBUS DP protocols, so it can slot into either a SIMATIC S7-based or third-party controller network without a gateway. The unit is a reversing starter, meaning it can control a motor in both forward and reverse directions from a single device. It supports reverse starting and does not support direct start — the reversing logic is built in. The main energy infeed uses a socket per ISO 23570, which is a standardized connector for motor starters in this class. Supply voltage is 24 V DC nominal, with a permissible range of 20.4 to 28.8 V DC. The unit draws its control power from this 24 V bus; the rated operating range covers the typical 24 V industrial supply with margin for ripple and drop.
SCCR and fault handling
The rated short-circuit current at 400 V is 100 000 A. Shock resistance is 15 g for 11 ms, and vibration resistance is 2 g. These figures are typical for machine-mounted gear; the starter can live on a press or conveyor frame without additional damping.
Mounting and I/O configuration
Mounting is by screw fixing in either vertical or horizontal orientation. Dimensions are 230 mm height, 150 mm depth, and 110 mm width — a compact footprint for a reversing starter with integrated fieldbus. The enclosure is IP65, so it can be mounted in a washdown area or outdoors without a separate enclosure. The unit provides 4 digital inputs via M12 sockets, and 0 digital outputs. The input byte count is 2 bytes; the output byte count is also 2 bytes. The brake control with 24 V DC is not supported. Power dissipation is 3.888 W both with and without the bypass circuit — the bypass does not add thermal load.