What it is and what it does
The Siemens 3RK1303-2AS51-1AA3 is a reversing starter designed for motor control in industrial automation. It switches motor loads up to 4 A in AC-3 duty at 400 V, which covers small conveyors, pumps, and fan drives that need forward/reverse operation. The IP65 enclosure means the unit withstands washdown environments — suitable for food-and-bev lines or outdoor installation without a separate cabinet. Rated supply voltage is 24 V DC, with a permissible range of 20.4 to 28.8 V DC, so it holds in during dips on a 24 V control bus. The short-circuit protection is rated at 100 kA at 400 V, meaning it safely interrupts faults up to that level without cascading upstream — critical for panel coordination studies. Communication is via PROFIBUS DP, with two M12 digital inputs for local sensors or pushbuttons. The motor protection uses a thermistor input, so it can directly monitor winding temperature on the motor side.
Integration notes
Dimensions are 130 mm wide, 250 mm high, and 107 mm deep — it fits a standard enclosure footprint but check the gland plate clearance for the hybrid plug and M12 connectors. The line-side infeed uses a hybrid plug; the load-side outgoing feeder uses a socket per ISO 23570. Brake control at 400 V AC is integrated, so no external contactor is needed for motor brake circuits.