Power To Outbuilding

[rightsaidfred]

I'm just looking at the feasibility of and cost of converting a small old outbuilding to a guest annex. I'd want to put in a separate CU running a shower (about 9kW) a little Redring wash basin hot water geyser, a couple of lights and a couple of sockets. The distance from the front of my house (where the existing CU is) to the outbuilding is about 40m (straight line). I know I'd need to lay an SWA cable but can anyone advise:
1. Would this need to be connected to the Board supply bypassing my existing CU?
2. What size SWA I'd need to lay given that length of run.
3. What other kit, if any, I'd need to have fitted to the "house" side of this set up?
4. Physically, where would I leave the ends of the SWA for the sparky to do his bit?

Thanx

 

[Steve]

That's gonna be expensive. 40m is a long way. 9kw is a lot of current. Given your power requirements, if money were no object i'd run 25mm² SWA, but you could probably get away with 16mm².

You'd need to split the meter tails and fit a 63A switchfuse at the house. Then fit an RCD consumer unit at the shed (the shed would probably have to be a TT earth supply, due to there being Extraneous conductive parts (copper pipes?))

Before you buy the SWA, have a word with your spark and see what size he wants to use. Take a picture of the SWA in the hole before you backfill, as evidence to show him that its been buried deep enough. He would probably want the SWA leading to near the meter in the house.

 

[ban-all-sheds]

9kW??

So someone's in the shower, when someone else turns the kettle on an then the hot water to wash their hands....

I don't know what you have in your house, or what your supply is fused at, but there's a very real possibility of overloading it.

Plus there's the fact to consider that you have to apply to LABC for planning permission and/or change of use for this building, so the whole thing will be scrutinised and need certifying etc.

 

[ban-all-sheds]

the shed would probably have to be a TT earth supply, due to there being Extraneous conductive parts (copper pipes?))

No - no more so than any other building with e-c-p's.

It's one of the options with a TN-C-S supply, but so is applying main equipotential bonding, and if the SWA is big enough the cpc in that can double as the bonding conductor.

 

[rightsaidfred]

Thanks for the help guys. I was looking at a small, 7kW, shower to keep the whole load down. You've more or less confirmed what I thought - that it's going to be a major part of the costing. A PP enquiry suggests no PP problem so it's just the hard work left.

Cheers

 

[Adam_151]

Do you have an electric shower in the main house? what about an electric cooker?

 

[ban-all-sheds]

A PP enquiry suggests no PP problem

What does that mean?

 

[Steve]

i'm too sexy for part p

sorry, i couldnt resist.

 

[rightsaidfred]

In no particular order:
Yes, there's an electric shower and cooker in the, main building.
The PP I was referring to was Planning Permission as that point had been raised.
And yes, far to **** sexy (and old!!!) for part P

25mm SWA it is then.... will 900mm deep be enough (otherwise I've got to route below a clay drain pipe (Is it all worth it, I ask?)

TTFN

 

[Adam_151]

with an electric shower and cooker in the main building, I think you'll be pushing it with your supply to be honest, I'm not sure what kinda figure I'd say for max demand (though certainly if you went by the OSG you'd be well over 100A) I guess it could probably 'scrape' by though

Usually 500mm is what SWA is buried at IIRC

As to whether its worth it, I don't think so, 40m of 25mm² SWA is going to be expensive, my advice would to forget the shower and just put in a few sockets and lights,

Also remember you have the cost of a water line, and a grey water drain as well (and a full drain if you want a bog) - [but thats all beyond the scope of the electrics forum ]

 

[Steve]

I would forget the SWA and get your DNO to provide a new supply for the outbuilding.

 

[ban-all-sheds]

Have you got gas?

 

[Steve]

Have you got gas?

<wonders where ban is going with this>

 

[ban-all-sheds]

Ban is going down the "get a combi boiler" route....

 

[securespark]

From what's been said, I'd go for a new supply. 40m (maybe more) plus a current demand of 12kW just for water heating shouts new supply to me!!