The Siemens 3RK1300-0KS01-0AA1 is an electromechanical direct starter from the SIRIUS EM 300 DS family, designed for the ET 200X distributed I/O system. It combines a motor-protective bimetal relay and a contactor in one IP65-rated enclosure, so it switches and protects a motor load directly without a separate overload relay. The setting range is 0.9 to 1.25 A, and at AC-3 duty (motor starting) on 400 V it is rated at 0.37 kW — that's the motor power it can switch under typical three-phase induction motor loads. It includes a motor brake output (DC 24 V / 3 A) for externally supplied brakes, which is a common requirement on conveyor and hoist applications where the load must hold position when power is removed. The unit communicates over PROFIBUS DP, so it can be controlled and monitored from a PLC without separate control wiring.
This is a distributed starter — it mounts in the field near the motor, not on a central DIN rail in the main panel. Dimensions are 134 mm deep, 140 mm wide, and 270 mm high. The main current circuit connects via tab terminals, and the 9-pole motor feeder and 9-pole power connection are built into the housing. Operating temperature range is 0 to 55 °C, which covers most factory-floor conditions but not freezer or outdoor direct-sun applications.
The 0.9 to 1.25 A setting range is the overload trip window — you set it to match the motor's full-load current. For a 0.37 kW motor at 400 V, the full-load current is typically around 1.0 A, so this starter covers that motor size exactly. If your motor draws more than 1.25 A, you need a larger starter. The PROFIBUS DP interface (yes, it has bus communication) means it can be integrated into a distributed control architecture — the PLC sees the starter's status and can issue start/stop commands over the fieldbus. No AS-Interface on this unit, so if your line uses AS-i, this is not the right variant.