I am working on the Canadian electrical code rules for grounding. Current rules in Canada require a #6 to artificial electrodes and the NEC is similar with UFER (concrete encased electrode) grounds at #4

What are the wire sizes in Europe from the neutral (grounded circuit conductor) to the electrode(s)?

AWG if it is speced but I can figure out metric.

Are there different sizes for different electrode types?

One more Question if a single ground wire serves multiple transformers using the same electrode how is that sized. IE a high rise with several distribution transformers. We call that a system ground.

Thanks in advance.