Cable, conduit, multi utilitiesTrench question.

[plugwash]

soory read a previous post which implied the length was unknown

i think given what you have mentioned 15KW would be a reasonablly conservative guess at max load (allows for the shower on one socket fully loaded and a couple of other bits on top).

so 15KW at 15m

you could get away with 10mm XPLE SWA but i would advise 16mm PVC or XPLE SWA (XPLE running at its max rating gets bloody hot so you have to be carefull about terminations)

i advise use of 3 core SWA to keep the earth fault loop impedance low.

at the house end i think running this through your existing CU is a bad idea. somthing like http://www.tlc-direct.co.uk/Products/WY108M.html (with a 60A fuse fitted) seems like a good bet. It will need to be henleyed into the tails which requires pulling the service fuse not something that we would reccomend to most diyers (thought there are deffinately diyers here who have done it).

at the outbuilding end a metalclad CU should be used to allow direct termination of the SWA. This should have some form of rcd protection. (either a full RCD box a split load or a non-rcd box with RCBOs)

 

[dw3101]

Agree with the above and that pool looks

 

[Lectrician]

Pools and PME is not recommended in the regs, and is not allowed by most REC's. Something to bear in mind.

 

[Welski]

Thanks for all the assistance guys.

Yes the trench is 15 metres long but the internal runs will add approx 10 metres to the overall length.

I might have mentioned I will be getting an electrician round for this project, its not that I'm totally inexperieneced in this DIY field its just that with the large loads and large amounts of water I wouldnt want anything to go wrong!

As I said my reasons for asking are mainly so I can get the cabling in (and gas and soil pipe) and get the trench back filled before it all collapses!

But many thanks for all the help, as usual the genorosity of contributors to this site restore my faith in humanity !

 

[plugwash]

16mm is still fine for that current at 25m

get some 16mm three core SWA (doesn't really matter if its PVC or XPLE) and put it in leaving enough slack at either end for your electrician to connect later.

diy sheds (and online sheds like screwfix and toolstation) wont stock cable this size and finding online suppliers can be tricky. Local wholesalers may be a good option but some of them charge a bomb to diyers.

to give you some guidance of what you should pay (prices per meter)
http://www.electricalshop.net/acatalog/SWA.html £3.14 inc vat
http://www.tlc-direct.co.uk/Products/SW16slash3.html 3.70 ex vat

if you shop around local wholesalers and they decide your custom is worth having you may be able to get prices quite a bit lower than this though.

 

[Welski]

Plugwash, Superb that answer pulls everything together nicely *.

I've been looking around again to day and based on the responses was trying to source some 16mm three core SWA.

I came across Tlc but not the cheaper site. The closest I got was this:

www.alertelectrical.com/product.asp?typeID=152&subID=0&prodID=3653

which comes in at £3.10 excl vat.

I suppose it now comes down to delivery. Its probably not the lightest stuff in the world.

* ALMOST!!
I will bury it 400mm down and cover with warning maker tape but is there anything specific I should do at the base of the wall where I bring the cable straight up out of the ground. I plan on running it vertically up the outside of a single storey extension then along inside the roof space to down inside the house to the CU.
Does the cable need any further shielding or can I simple cleat it to the brickwork?

Guys once again thanks.

 

[plugwash]

you can cleat it to the brickwork SWA is fine outside

the marker tape shouldn't be right on top of the cable. it should be far enough above it that a guy can put his digger bucket through the warning tape BEFORE he destroys the cable.

 

[Welski]

it should be far enough above it that a guy can put his digger bucket through the warning tape BEFORE he destroys the cable.

Shame they didnt put something similiar above that shallow water pipe when I was digging this damn trench!