Just talking to my next door neighbour. He's currently got a very long
extension cable strung across the road, on top of the tarmac, between his
house and his lambing shed. Call it 100m to be on the safe side.

He's going to run armour cable through the gulley under the lane, but is
wondering what size. Reckons he'll chuck a 20A RCD on the house end -
it's not much more than a bunch of light bulbs and the odd heat lamp, but
it'd be nice to have a socket there he didn't have to worry about using.

He was thinking 4mm2, but wondering if 6mm2 would be wise.
I found a cable calculator on t'web, and it reckoned 10mm2 for 16A or
above, 6mm2 for 13A.

What think the assembled multitudes?