Cable down to the shed

[ppppenguin]

Sorry, got confused. 10mm armoured isn't cheap and not mormally needed for a few sockets and lights. Unless it's a very long run and there's a volt drop problem.

The trouble with using the 3rd core for earth bonding is that the CPC (circuit protective conductor, earth to most of us) isn't the same thing as an equipotential bonding conductor. AFAIK you can't use the same bit of wire for both. If you had 4 core armoured it would be different. You could then use separate cores for CPC and bonding.