mains tails via swa

[a-z electrics]

What advice can you give concerning running a 3 metre run of mains tails under ground from the meter head to a new CU in a newbuild property (barn conversion)? and what size would you say?
I'm assuming at this stage the earthing will be tncs.

The requirement is 100A and I see in the TLC catalog that 16mm 2-core is specced at 110A.. so could use 2 core with a separate 10mm/16mm earth? or best to go for 25mm 3-core? (big difference in price.. )

Ive used swa before but not in such a size.. or would it be a better option to use ordinary mains tails thru a metal duct?
The only problem I can see with a tube/ducting is to slow bend it upwards at each end and I guess you would still need to bond the tube but not to faff around with terminating it with conductive glands..
Cheers

 

[Clive P]

Hi,

16mm 3 core from TLC is 6.56/mtr, 25mm 3 Core is 7.80/mtr; so for 3 mtrs that's a difference in price of £3.72.

Regards.

 

[a-z electrics]

Hi,

16mm 3 core from TLC is 6.56/mtr, 25mm 3 Core is 7.80/mtr; so for 3 mtrs that's a difference in price of £3.72.

Regards.

16mm 3 core is only rated at 94A, so its not an option..

 

[Clive P]

Hi,

It was just the price difference for 3 mtrs I was highlighting.

Regards

 

[Leesparkykent]

Under ground or under floor boards with joists etc?

 

[a-z electrics]

Under ground or under floor boards with joists etc?

Its will be under ground but obviously theres the up/down drops to and from the two DBs so we're prob talking a total run box to box of around 8metres. The new building isnt built yet, so this is why Ive been asked to suggest best way to supply it.. its from an existing building (barn) but the distributor has yet to run the supply to it. So once thats done, there will be plenty of leeway to dig a trench and run the cables up the wall internally, before floorboards etc are put down,
Having looked up the cost of 2x2 galvanised trunking and end bends, I think Ive answered my own question as to which is cheapest.. !!

 

[Leesparkykent]

Id run in an SWA. If I was you id actually look in the book for the CCC of the SWA and not take the ones from the TLC website as gospel as the figures you have quoted from them don't seem right. I haven't looked as onsite atm. The figures you have may be for xlpe at an operating temperature of 90 which means all the terminals would also have to be rated for this also. And the the lower value for the 3core SWA is because that values is for 3phase not single phase and using the third core as a CPC.

 

[Darkwood]

Its will be under ground but obviously theres the up/down drops to and from the two DBs so we're prob talking a total run box to box of around 8metres. The new building isnt built yet, so this is why Ive been asked to suggest best way to supply it.. its from an existing building (barn) but the distributor has yet to run the supply to it. So once thats done, there will be plenty of leeway to dig a trench and run the cables up the wall internally, before floorboards etc are put down,
Having looked up the cost of 2x2 galvanised trunking and end bends, I think Ive answered my own question as to which is cheapest.. !!

You will need to run SWA either directly buried or in cable ducting, to calculate the required size you need to do your calcs for a cable that is buried as this will reduce the CCC although not much with your short run length (refer to your copy of the BS7671, not a free cable calc site), the depth of which it is buried would be circumstantial regarding the nature and use of the ground you intend to bury it under although gardening equipment, other trades digging in the future all need to be taken into account, I would not be using galv' trunking under any circumstances.

Your earthing requirements would depend on your barn and its construct and whether the other services are supplied in metal.

Ball park guess if your front end is 100amp in your SW/F would be 35mm 3core swa (can't remember 1ph 25mm rating in duct), if this is out of your experience then don't be afraid to employ someone and work alongside them to gain the experience for future reference, don't try wing such a job by using the internet for advice as there may be factors not mentioned that could be important to design.

 

[a-z electrics]

Thanks to everyone who has responded, I have learned a few things and of course I shall look up the regs figures for the CCC( I'm not at home at the moment). Hope your day goes well