What it is and what it does
The Siemens 3RK1300-0BS01-1AA3 is a reversing starter with electromechanical switching contacts, designed to control the direction of three-phase motor loads in an enclosure. It carries a bimetal motor protection element and includes a motor brake output. The unit communicates over PROFIBUS DP via the backplane bus, making it a networked motor control component for automated lines.
Key ratings and what they mean for fit
The IP65 protection class means the enclosure is dust-tight and protected against water jets — suitable for washdown environments or outdoor installation where the starter is mounted directly on a machine frame rather than in a sealed cabinet. Rated 50 A at 400 V for the main current circuit (three-pole). That is the thermal current rating for the power path — the maximum continuous current the contacts can carry in a resistive or lightly inductive load. The AC-3 motor switching rating is 0.2 A at 400 V, which governs the actual motor load it can switch under full starting current. The 0.2 A figure corresponds to a 0.06 kW motor at 400 V AC-3 duty — small fractional-horsepower motors like conveyor drives or valve actuators. Supply voltage is 24 V DC nominal, with a rated range of 20.4 to 28.8 V DC for the control supply. The control electronics and coil hold-in are designed for this range; dropping below 20.4 V risks dropout. Operating temperature range is 0 to 55 °C during operation. No derating curve is provided in the base spec, but the upper limit is typical for panel-mount gear without forced cooling.
Integration and mounting
The unit measures 140 mm wide by 270 mm high by 134 mm deep. It is a self-contained reversing starter with sockets for main energy infeed, load-side outgoing feeder, and supply voltage line-side via the backplane bus — all conforming to ISO 23570. This means it plugs into a standardized backplane system for power and communication, reducing point-to-point wiring. The IP65 enclosure allows direct machine mounting without a separate cabinet, saving panel space. Short-circuit protection is provided by circuit-breakers (designed into the system). The starter has no integrated digital inputs or outputs — all I/O is handled upstream via the PROFIBUS DP network.