So are you going to give each cabin 30amps of 3 phase supply ( You said your main breaker was 60amp I assume 3 phase 60amp)
So if the cable works out at 50mm and is the most expensive part of the install, then why don't you fit 2 x 32amp 3 phase breakers under the existing 60amp one, and run 2 X 3 phase 32amp supplies out, you most likely would get away with 16mm and possibly 10mm if you had a better idea of your loads
Ok, that sounds like a winner, I'll get my head back in the books and work out sizes based on 2 32amp instead of 1 60amp. It'll also have the advantage of the rennovation sparkies having the option to supply the 2x32a board from a different place if they need to rip out the existing con unit as part of their work.
I'm going to take a guess at the proposed load per cabin.
2x 3phase lathes or pillar drills
6x 5' flurescents
1x pc workstation
various low powered hand tools. ie, soldering irons.
5x heat guns that may concievably be used at the same time.
2x 2kw convectors when it gets colder.
1x 13amp plastic former
Cable run is through ceiling void to outside, no applicable grouping, thermals or insulation. Clipped direct on wall, 3m duct under steps, clipped direct to fence, 1m duct under gateway, grouped with 32amp single phase swa along fence to cabins.
What size(s) would you go for?