Since we have an external Safety SPS I have to wire the EM-Stop Button from the UR5e to my Safety SPS.
Are there a documentation like wiring diagram from the EM-Stop and how to disconnect it from the UR5e?
TY 
You can pass the emergency stop signal through to the Configurable Outputs. You can read more about it in the user manual.
Manual can be found here: UR Download | Support Site | Universal Robots
You’ll also have to change the Installation to set up the Configurable Outputs for Emergency Stop.
Unfortunately there is only the “Emergency Stop System” Signal. So when I pull out the EM-Stop Button the “Emergency Stop System” is still “LOW” till you reset the Robot.
This means I cannot reset the master safety system.
At the same time I cannot reset the Robot since the master safety is not reset.