Shaun,
Electrical wire /cable sizes went metric in the UK in the middle 70's, that's over 35+ years ago!!!
The point is that now, The whole world, except the USA, and it seems Canada too, ... is Metric...
As it happens, i've just been looking up the latest NEC tonight, and see that you are still using what we used to call ''Screw-it'' wire connectors everywhere. These things were banned in UK over 40 years ago, and probably longer in parts of Europe. I've had lots of experience of the NEC from working on overseas projects where the NEC was initially the projects electrical standard. It caused nothing but trouble. It's standards are out of date, vague in important areas, nitpicking in others. And sometimes completly incompatible with equipment and materials from countries outside of the USA....
David....