The Siemens 3RK1908-1SK00 is a SIMATIC-branded motor starter kit configured as a reversing starter — meaning it can start a motor in either direction without an external contactor interlock. The unit is pluggable into a BaseUnit, so the power and control wiring stay in the panel while the electronics module swaps out — useful for quick replacement or commissioning changes without pulling wires.
The headline rating here is the short-circuit current rating: 55 kA at both 400 V and 500 V. Trip class is adjustable — CLASS OFF, 5, or 10 — so you can match the overload curve to the motor's starting profile. Class 10 is standard for most general-purpose motors; Class 5 for fast-starting loads like pumps; OFF disables the overload function if you're using an external relay. The 4 digital inputs are onboard for local control or feedback, and the unit supports both PROFIBUS DP and PROFINET protocols, so it drops into either a legacy fieldbus or a modern industrial Ethernet architecture without a gateway.
Dimensions are 150 mm deep, 30 mm wide, 142 mm tall — the 30 mm width is a single module width on a standard DIN rail, so it fits tight panels where space is at a premium. Clearance above and below the unit is 50 mm each direction for airflow and wiring access. Shock rated to 6g at 11 ms, vibration to 2g up to 500 Hz — suitable for machine-mounted applications near conveyors or presses.
No last-time-buy or surplus-channel urgency applies here.