Thank you all for your feedback!

"The most widely used residential arrangement for receptacles is the ring circuit, fed from a 30 or 32A fuse or circuit-breaker. Our plugs then contain a cartridge fuse, the maximum rating of which is 13A. That's why polarity of wiring at the socket is considered so important here, because if you swapped the line and neutral then the fuse in the plug would be in the neutral line.

You'd be left with the 30 or 32A fuse at the main panel as the only protection against shorts to ground. For most appliances the actual polarity of supply on the cord is unimportant, and these days you'll find the same model sold right across Europe with just a different plug.

In TT systems there is a main RCD (GFI) which would obviously provide ground-fault protection in this situation. Although RCDs are becoming increasingly common in TN systems as well, they are not required, and therefore with reversed polarity you could end up with a 0.5 or 0.75 sq. mm cord having no better protection than a 30A fuse."

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?

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.

Here TN systems are used only in industrial systems, where there is a HV distribution next to the installation.

"I'm not quite sure I understand your terminology here. Do you mean a 230V delta system? Or maybe a 133/230V wye system without the neutral brought into the house? "

I meant a 133/230V wye system without the neutral brought into the house. These are older installations, where at the time used to be 110V.

" By the way, I'm not sure how you tried to post the picture you referred to, but if have any problems feel free to e-mail me and I'll explain how to do it. Alternatively, e-mail the picture to me as an attachment and I'll post it for you."

Yes, please explain how to do it.

The other "odd" American system (from a European perspective) is the 4-wire delta where the ground is at the mid-point of one side of the delta. Always 240V between any two phases, but two phases measure 120V to ground and the third is 208V to ground. I'm not aware of any such system ever being used on this side of the Atlantic.""

Very interesting, this 4-wire system! Never heard of it.