OK Just a quick question becouse I am away from my office and can not get a hold of my 16th Regs till Monday.
Friend has just phoned (I have not seen this set up yet) he is building a summer house in his garden timber I suspect. He plans to install power via 35 Meter 10mm sq SWA.
I recon the cable would be ok but I would like to see it supplied from a 40amp RCD to a small consumer unit in the summer house with a earth spike. ( I do not know eathing set up in his house at the moment)
Thanks for your reply. I am happy with what you say about the DBs at each end.
I have not worked it out yet but I thought the 10mm would be sufficent regards the voltage drop and relatively small load.
What did concern me more was the fact that it is extraneous of the dwelling and such a distance from it. So you recon earthing through the cable and the armour would be sufficent, and a spike would not be required
My interpretation of the current regs. would also be that the 10mm is fine. If you are going to use an earth "spike" ( which may of course need more than one, depnding on soil resistance) then you would be advised to make it a TT system (with RCD) totally independent of the house earth. Remember also that if you choose this option you must dig down at least 600mm BEFORE you knock in the earth rods, to ensure a good connection. Otherwise stick to using one core and sheath of the SWA, remembering that if you have any extraneous metalwork in the summer house, e.g. pipes, these must be bonded as normal.
What sort of load is going to be in the summerhouse? While I'm all for over-engineering to "be on the safe side" and to allow for future growth, I'm wondering what's going to be in there to warrant a 40A subfeeder. A 30A subfeed with 6mm SWA would still be within voltage-drop tolerances, even at full load.
If the hosue is PME, then a TT system with separate earth rod at the summerhouse might be the way to go (yes, I'm trying to put aside my personal dislike of TT arrangements ).