What this part is and what it does
The Siemens SIMATIC 3RK1308-0DD00-0CP0 is a fail-safe reversing starter designed to safely control and reverse motor loads in industrial automation. It's a 4 via 3DI/LC module, meaning it integrates four digital inputs and a load circuit into a single unit, reducing wiring and panel space. This part is built for safety-rated applications where a controlled stop and reversal are required, like conveyors, hoists, or any machine with a hazard zone that needs guarding.
Key ratings and what they mean for fit
The trip class is adjustable — CLASS OFF / 5 / 10 — so you can match the thermal protection to your motor's starting characteristics. Trip Class 10 is the standard for most general-purpose motors; Class 5 is for faster starts; OFF disables the thermal model if you're using an external overload relay. The minimum load is 50% of the smallest adjustable rated current, which means you can't run a motor that's too small for the starter's range — keep that in mind when sizing. It operates on 24 VDC nominal, with a permissible range of 20.4 V to 28.8 V. The ambient temperature range during operation is -25 to +60 °C, with derating above that. The safe state is load circuit open, meaning when the safety function is triggered, the starter opens the load circuit and stops the motor. ON-delay time is 35 ms, OFF-delay is 35 to 50 ms — fast enough for most safety applications but verify your system's required response time.
Where it goes in the panel
This module is pluggable into a BaseUnit, so it snaps onto a DIN rail and connects to the backplane bus. Width is 30 mm, depth 150 mm, height 142 mm — fits in a standard 30 mm slot. Mounting position can be vertical or horizontal, but observe derating if horizontal. Vibration resistance is 15 mm at 6 Hz, 2g up to 500 Hz; shock resistance is 6g for 11 ms — tough enough for a machine-mounted panel but not for direct motor vibration.
Communication and I/O
It supports both PROFINET and PROFIBUS DP protocols, so it can talk to most Siemens controllers and many third-party PLCs. The input data is 4 bytes, output data is 2 bytes — that's the process image for the safety and control signals. One safety-related channel is present, which is typical for a fail-safe starter.