The Siemens 3RK1303-2AS54-1AA0 is a SIRIUS 3RK1303 reversing starter — a motor-reversing contactor assembly with integrated overload protection, built into an IP65-rated enclosure for direct machine mounting.
The AC-3 rating of 4 A at 400 V is the motor-switching current, not the resistive load rating — expect to use it with a 1.5 kW to 2.2 kW motor on a 400 V three-phase supply. Motor protection is via thermistor input (PTC), so the motor must have a PTC thermistor embedded in its windings — this is standard on IEC motors, but verify on retrofit jobs. The reversing function is built in, meaning two contactors mechanically interlocked inside the housing, so no external interlock wiring is needed. It is not IP67 or IP69K, so do not submerge it or direct high-pressure steam at it. The 24 V DC control supply (rated 20.4 to 28.8 V) is standard for PLC-driven panels; the coil holds at 24 V nominal and drops out below 20.4 V. Communication is via PROFIBUS DP (the unit has a PROFIBUS DP interface, not PROFINET), which means it integrates into a classic fieldbus architecture — not a modern PROFINET ring. The hybrid plug/socket on the line side carries both power and communication, using the ISO 23570 connector standard. Two M12 digital inputs are on board for local sensors (e.g., limit switches for end-of-travel), parameterizable via the bus.
Dimensions: 130 mm wide, 250 mm high, 107 mm deep. It mounts via integrated fixing points or the ISO 23570 socket.