I've just learned about the surge protection device (SPD). As I was reading about its connection in a three phase line, I came across this scheme:
I understand that the SPD's are there to limit the line tension in respect with the PE reference, but why isn't it connected to the line neutral? Each phase's voltage should be measured like this in my mind:
Also, isn't the protective ground meant to protect things that are outside the circuit? like other electronics, people etc. against accidental contacts?. How can you intentionally connect the circuit with a reference that is only there for safety?