Shed Electrics

14 Feb 2007
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United Kingdom
I have read some of the numerous comments on this site which has proved very helpful. I propose to run a supply to the shed via a fused spur from the back of the house since the main consumer unit is right at the front of the house and it would cause an awful lot of drilling etc to run it from there. The proposed setup would be, fused spur from kitchen socket with 2.5mm t&e, 2.5mm t&e to external junction box, 4mm or 6mm swa from junction box to CTI Garage unit [] I would like to run a 2 gang internal and a 2 gang external socket from this cu for occasional power/garden tool use and also a light (presumably via a fused spur) Does this all sound feasible?[/url]
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If you have read the numerous posts recently about shed electrics you will have pretty much all the answers you need, although you don't seem to have taken any notice of the advice given thus far.

Your kitchen should be RCD protected so you don't need another one in the garage, doing so would be pointless and a waste of money.

Try to use as few joints as possible. It may seem like a lot of extra work to run a feed from the CU but it isn't a good idea to spur from a socket circuit.

If you decide to ignore this advice though, answer the following:

How far from the socket the spur will be taken from to the shed?
How far from the CU to the socket?

Remember that you are limited to 13A due to the fused spur so depending on the voltage drop 2.5m^2 SWA may well be all you need.

This work is notifiable, etc...

Thanks for the prompt advice. I guess that it would be preferable to run from the main box but it really would be a pain - through 2 rooms and a staircase. The only reason I was going to run the SWA from an external junction box is that I thought it may be difficult to feed through the wall at an appropriate angle


Socket to spur is minimal. Distance to shed is approx 25ft
Well that is your choice, but since you are going to have to have this work inspected you might want to ask them for their take on your idea because if they won't accept it you have wasted your time.

You will also have to factor in discrimination issues. A fully loaded 16A + 6A MCB will not trip but the 13A fuse at the house will.

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Ok, I can feel the negative vibes all the way over here :)

If you think it's a bad idea running from a socket then I may just give up and get myself a 10m extension lead with multiple sockets and plug it into a kitchen socket when I need to.

Presumably the power load would be the same so it puzzles me why it would be a problem - but hey, I'm in the company of people who know what they're talking about.
I'm trying my best to be as helpful as I can but there are so many ways to do a job badly and only a handful of ways to do it well, so I'm just trying to make you see the difference :)

The power load whether on an extension lead or the SWA will be the same but the difference is that with the SWA you are running fixed wiring into a separate consumer unit with it's own protective devices. It's not the same issue with as an extension lead which is protected by the fuse in the plug and only that. By introducing multiple protective devices you start messing around with the order in which they will operate. They should operate in the order closest to the fault but this isn't guaranteed with your plan. It may not be an issue as you may never blow the 13A fuse but it is something that has to be considered.

As this work is notifiable I think you should consult the people who have the final say in the matter, they may have no problem with your plan and you can carry on and never have any problems.

arb1, the best way to provide power in the manner you describe is as follows:

FCU in house
2.5mm² t+e to metal adaptable box
2.5mm² SWA through wall to shed/garage?
Terminate SWA onto metalclad socket, then run T+E to other accessories.

You dont need a consumer unit at the shed/garage. There's no point.
Many thanks, I was concentrating all my efforts on putting a CU in the shed as a central point for my 2 sockets and light. Wasn't sure how to arrange the power supply once I got it to the shed!
Would I need a DP switch or socket before I run to the first socket in the shed?

Are 3amp FCU's freely available - can't see any on Screwfix etc. Could I just buy a 13amp one and change the fuse to a 3 amp?
arb1 said:
Would I need a DP switch or socket before I run to the first socket in the shed?

Are 3amp FCU's freely available - can't see any on Screwfix etc. Could I just buy a 13amp one and change the fuse to a 3 amp?

That's exactly what you do (you can't buy a "3 amp" FCU as such). If you use a switched FCU in the house you can isolate the shed totally if necessary.

Not a bad idea to put a 20A DP switch feeding the sockets in the shed, but I wouldn't put the lights on it, so that you can work on the sockets if you need to and still have light in the shed.

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