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Now I understand why the UK uses fused plugs! So, in the panel board you have only one fuse for all circuits? what about the lighting?

A ring main is still only one circuit. If there are more circuits, you obviously need more fuses.

Lights in the UK are on separate circuits )between 6 and 16 Amps). How are lights wired in Belgium? I've read that France has separate circuits, but I know a lot of countries that don't. (E.g. Sweden)

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Regarding your TN system:
If I understand correctly, the only protection you have is from the fuse (where no gfi is installed). Then most probably you use only B curve fuses? And the ground cables must be very big diameter for adequate protection.

The TN system is standard in a number of countries, including the US, Germany, Denmark, Sweden etc. It's really France and Belgium who are the odd ones out here [Linked Image]
There is no need for the ground wire to be larger than the other wires. (The Brits make it smaller! This is not a practice shared by neither Americans nor other Europeans as far as I know.) It is sufficent that the fuse blows or breaker trips within a few seconds.