Outside electrics - cable size?

[daweorama]

I intend to run a swa cable from my house down to the stables run is about 75mtr. It will only have light usage say 3 lights and 3 double sockets. My question is what size swa shall I use?

 

[hairyben]

What you gonna be plugging in?

Ideally I'd go for a least 6mm, but if you've got nothing heavy duty in use you'll get away with a smaller supply.

 

[Spark123]

What sort of appliances will you be plugging in? Any electric heaters?
For say a 32A circuit over that sort of distance you'll be talking about 25mm² 2c XPLE SWA, also where livestock is involved you need to take special precautions, what is your earthing type?

 

[daweorama]

Nothing high powered certainly no heaters the livestock have feathers to keep warm!! The main reason for putting electrics over is to provide lighting and just put the sockets there for future use. Ive heard from someone else that i may have to put a local earth spike in due to the livestock is this true?

Thanks for your responces!!

 

[ericmark]

Issue 16 Autumn 2005 Wiring Matters see http://www2.theiet.org/Publish/WireRegs/WiringMatters/index.cfm has a very good article called Electrical installations outdoors: a supply to a detached outbuilding I would read this to start with. As you say Fig 705 in BS7671:2008 shows some very complex earthing arrangements required because of the added danger when walking without shoes on a wet floor on four legs. If I read you correct your live stock only have two legs so although technically it may apply I would not worry too much. As to using a TT supply or exporting the TN-S earth it will depend on metalwork which is outside the shed once you have read the wiring matters maybe we can return to that. If you are not using 6mm 3 core or above you may be forced to TT supply as the earth bonding will not be big enough anyway. For 40 amp at 75 meters you need 16mm at 25 amp down to 10mm and both 20 amp and 16 amp brings it to 6mm at 10 amp then 4mm and 6 amp needs 2.5mm so a 20 Amp MCB or RCBO and 6mm does seem most likely to fit your needs.
Size has be calculated on 5% volt drop since lights are involved should work on 3% volt drop which would need 10mm for 16 amp supply so maybe select somewhere between and 6mm or 16 amp supply?
Eric