What it is and what it does
The Siemens 3RK1300-0JS01-0AA4 is an EM 300 DS electromechanical direct starter from the SIRIUS family, designed for the ET 200X distributed I/O system. It's a fully integrated motor starting solution that combines a contactor, bimetal overload relay, and short-circuit protection into one IP65-rated enclosure. Rated at 0.25 kW at AC-3 duty on a 400 V supply, it handles small three-phase motors — think conveyor drives, pump motors, or small fan loads on a distributed line. The setting range of 0.7 to 1.0 A means you dial in the full-load current of the motor, not the frame size.
Key ratings and what they mean for fit
The 0.25 kW AC-3 rating at 400 V tells you this starter is sized for the smallest motor class — fractional horsepower, typically below 1/3 hp. The 50 A short-circuit breaking capacity (Icu) at 400 V means it safely interrupts faults up to that level without cascading upstream, as long as the upstream protective device is coordinated per IEC 60947-4-1. The bimetal overload provides inverse-time thermal protection — it tracks the motor's heating curve, so it's good for standard induction motors with normal starting duty. Not for frequent starting or reversing applications where an electronic overload would be a better fit. IP65 means the whole enclosure — not just the optics — is dust-tight and protected against low-pressure water jets. This unit is meant for washdown zones, outdoor cabinets, or anywhere dust and moisture are a problem. The tab terminals for the main circuit are a quick-connect style, common in distributed motor control centers. The built-in motor brake output handles DC 500 V / 1 A for internally supplied brakes — think holding brakes on vertical-axis motors or conveyor stops. That saves an external brake rectifier and relay.
Bus communication and integration
PROFIBUS DP onboard means this starter talks directly to a PLC without a separate gateway. It's a bus node — you get start/stop, fault feedback, and current monitoring over the network. The 9-pole motor feeder and 9-pole power connection are the physical interface; they plug into the ET 200X backplane. Operating ambient range of 0 to 55 °C is typical for industrial control cabinets. No derating data in the spec, but keep the enclosure ventilated if you're packing multiple units side by side.