What this reversing starter packs
The Siemens 3RK1300-0KS01-1AA3 is a SIRIUS EM 300 RS electromechanical reversing starter designed for the ET 200X distributed I/O system — it combines two contactors, a bimetal overload relay, and a motor brake output in a single IP65 enclosure. Rated 0.37 kW at AC-3 duty on a 400 V supply, it covers the small-motor end of the line: pumps, conveyors, and valve actuators that need forward/reverse control without a separate reversing contactor pair. The setting range of 0.9 to 1.25 A (full-scale value 1.25 A) means the bimetal overload matches motors drawing between those FLA values — common for 0.37 kW four-pole motors at 400 V. The 50 A short-circuit breaking capacity at 400 V (Icu) tells you it coordinates with upstream protection up to that fault level without welding the contacts. The 9-pole motor feeder and 9-pole power connection (tab terminals for the main circuit) handle the reversing wiring internally; you land one motor cable and one supply cable.
PROFIBUS DP and brake output — what they mean on the line
Built-in PROFIBUS DP communication (yes, the protocol is confirmed) lets this reversing starter take start/stop and direction commands directly from the fieldbus — no separate I/O block needed for the motor branch. The integrated motor brake output (24 V DC type per the voltage class) powers an external holding brake, so a vertical-load conveyor or gantry axis gets its brake released when the motor runs and set when it stops, all from the same unit. Ambient temperature range of 0 to 55 °C is standard for indoor machine-mount; derate if the enclosure traps heat above that.