The Siemens 3RK1903-0AK10 is a 65 mm terminal module purpose-built for the ET200S High Feature DOL starter family. It serves as the wiring interface between the distributed I/O backplane and a direct soft starter — no separate supply line connection needed, meaning it draws power and comms through the ET200S rail itself. This keeps the cabinet wiring clean and the footprint tight: one module width, no extra feed terminals.
It occupies exactly one 65 mm slot in the ET200S station, so the panel fill factor is predictable: you can calculate how many starter modules fit per meter of rail. The direct soft starter variant means it handles motor starting without the mechanical wear of a contactor — good for frequent start/stop cycles on conveyors or pumps where you want controlled acceleration.