I always understood that one of the two purposes of protective earthing is keeping the electric potential difference between the chassis of a devide and the ground (the ground I am standing uppon while using this device) at a low rate, preferably lower than what is considered harmful to the human body. However, looking at this particular realisation of the protective grounding (TN-Net) there is something I don't understand:
The PE-Connection will keep the chassis at the same Potential as the ground located at the star point of the system. However (as this question indicates), the ground I am standing on in the moment I am touching the device may have a different potential than the one that exists at the point where the network is grounded. How will this help me not being shocked?
EDIT: I know that there are other protective measures, like the RCD shutting down when it detects a difference between the L1 current and the N current. I'd still like to know wether the difference in potentials do have an effect (or why they don't have an effect).