any advice appreciated supply to garden shed

[714gold714]

Hello there
Just after abit of advice got a supply to run to a garden shed for family friend, he wants x2 lights and x3 sockets its a run of 35 metres.

I was thinking of running a 2.5mm 3 core SWA clipped and underground (i have completed volt drop calcs and 2.5 is sufficient) from a non RCD protected board(20amp mcb) then straight into the shed with a 2 ways RCD main switch consumer unit earthed via a earth stake. My question is do you think that 2.5 is to small shall I fit a 6mm or 4mm SWA. He will be plugging in wood tools eg saws etc that draw very few amps and just 2 70W flourescents.

Any advice is appreciated as hopefully useing this job as part of my assesment

thanks

 

[malcolmsanford]

Yes I would go for a bigger size cable, If he plans to work out there then he may want to have a little fan heater, for the winter,perhaps a kettle, you never know. Plus if your going to dig X amount of metres then you only want to do it once and so put a bigger cable in.

Hmmmmmmmmmmm ok have to go down this road, is there a reason your going to TT the shed?

 

[Engineer54]

Never install a sub-main cable that can only just cope with the present requirement and the parameters covering the installation method etc. I would always up a size or two, for any future requirement, that invariably will come!!

Why are you going to use an earth electrode for the shed's earthing? Is it a PME system and that the shed has extraneous parts within?? That would be the only reason i would TT this shed, and then, only because of the 35m distance. Other than that, use the SWA, or a 3rd core within the cable.

 

[714gold714]

thanks for the reply I think im going to put a bigger cable in.
The only reason I was going to put a earth stake was for an added extra level of safety, but second thoughts it could make things worse as the supply to the house is TNCS and the board i will be coming from to feed the shed is fed from the house. How would you go about earthing the installation?

 

[topquark]

It depends what is meant by "wood tools". My combination machine has a dedicated 16A supply just on it's own, there are plenty of woodworking tools that need that sort of supply.

It's only about 25% more for 6mm over 4mm 3 core.

 

[Engineer54]

Depends very much on whether you have extraneous parts within this shed.

 

[714gold714]

no extraneous parts withing the shed, iv checked all the wood tools all off a plug top fuse that mainly use very little amps, mainly are just saws. Im going to be fitting a 6mm cable from a 32 amp fuse, so do you think it will be best to keep the shed as a pme supply? and no earth stake just use a core of the swa as my earth?

 

[malcolmsanford]

If you don't have extraneous conductive parts then yes you could indeed just get a 3 core SWA and use the 3rd core as the CPC. Just then earthing the SWA at the house end.

Or if you decide to use the SWA has the CPC in a 2 core cable, then earth the CPC at both ends.

 

[714gold714]

excellent all sorted thanks for the advice much appreciated!

 

[Engineer54]

no extraneous parts withing the shed, iv checked all the wood tools all off a plug top fuse that mainly use very little amps, mainly are just saws. Im going to be fitting a 6mm cable from a 32 amp fuse, so do you think it will be best to keep the shed as a pme supply? and no earth stake just use a core of the swa as my earth?

Absolutely!! ....

Just follow Malcolm's recommendations above regarding your earthing arrangements and it'll be a good-un!! And a dammed site safer for your mate too. Now your RCD will be giving additional protection to this installation, instead of the Only protection!!!