Cable down to the shed

[ppppenguin]

I thought you said you were using 3 core 4mm armoured. Hence all 3 cores are 4mm. One core certainly won't be 10mm. Don't rely on the armouring for earth continuity. It can be done but you need to be very sure of your clamps. Calculating the equivalent copper area of SWA is a faff too, though I'm sure there are tables somewhere.

If you're exporting the PME then you could always run a length of 10mm green/yellow alongside it to give a decent earth bond.