As it seems this forum is the best place for all sorts of knowledge, here goes.

I've got a terraced house, my garden is rather small, and at the end of it, about 6 metres from the house is a very nice summer house (wooden outbuilding, about 3x5m).

I want to turn that into a studio/office, but at the moment it's not wired for electricity...

The load in there won't be very high - some PC equipment and hi-fi, a couple of lights and a tiny fridge for beers. I'm looking at a couple of double sockets and two light fittings.

The garden has large paving slabs which can just be lifted up, so I can easily lift them, and dig a 18" deep channel.

Now my consumer unit has a couple of non-RCD spare slots on it, but unfortunately it's located in the front of the house, and I cannot run anything under the floor.


So I have two options:

Either I can take off power from an existing socket in the kitchen (already RCD'd but I would put in another one of those plug-in RCD jobbies to stop the wooden outbuilding setting off all my sockets at home). That obviously limits me to 13amps on that socket, but that's more than enough. I need to check what the total pull on all the house socket circuit can be but I imagine it's more than hefty! The total length of cable run from socket to outbuilding in this case would be less than 10m.

The other option is to run a cable 5m from the CU directly against gravity into the loft, run it across the loft to the back of the house, then run it down the outside rear wall, then again via trench to outbuilding. Total cable length in this case I imagine would be something like 40m..
If I did this, I could get a garage CU (1 RCD, 1 lighting and 1 non-RCD circuit) and install it in the shed. I wouldn't be able to do this if I feed off the kitchen socket as anything on the non-RCD would trip the house again.




1) Is my thinking sane?

2) Which is the better option? I understand option 2 seems to deliver a better overall wiring circuit in the outbuilding, but I imagine I'd need heftier cable, and a LOT more of it.

3) I would be using SWA armoured cable for anything that's running through the garden, but in the case of the second option am I okay using non-SWA stuff to run it up and across the loft?

4) Running it underground, can I just get a PVC conduit and run the cable through it? I'd also leave a snake rope or something in there in case I'd want to run another cable down there without tearing the garden up.

5) I seem to read a bit about various earthing/grounding issues when wiring an outbuilding, but am clear as mud on this issue. It's a completely wooden (excluding nails lol) building, that sits on concrete blocks, and has felt roofing. Is there something particularly complicated I need to do with regards to earthing the shed?



It's doing my head in, and that's before I start thinking about certification/building consent and god knows what! Back in Cyprus I did a very good and competent DIY job of most things, yet it seems I'm inadequate here in the UK to so much as screw in a light bulb! I'm quite happy for someone to give me a nod of approval on the work I've done, but I'm certainly not paying somebody to do all this.

Cheers
Pavs

not a sparky or an aproved person, but here's what I'd do.

Visit Screwfix & get some 2.5mm twin & earth cable to run from the CU, take this to a point where you can run it outside. Next get an IP64 or IP65 rate box (waterproof) and some choc box jointers (asuming the IP rated box does not have connectors) & run armoured calbe to a "garage CU" with two RCD's one for ring main (sockets), one for lighting. then you're good to go.

Hope that helps!

Hi I am a sparky and would do option2 like he says above

I would go for 4mm not 2.5 because of the lenght of run and the fact the cable will go underground.

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Originally posted by big-vee-twin
Hi I am a sparky and would do option2 like he says above

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Well why dont you offer up a solution?

And tell me why using RCD's is dangerous and why using fixed connectors inside an adaptable box is dangerous too?

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Originally posted by big-vee-twin
Well why dont you offer up a solution?

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quote:

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And tell me why using RCD's is dangerous and why using fixed connectors inside an adaptable box is dangerous too?

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simples

buy a cable real from homebase, and a electric fan to keep the plug cold, tie wrap it to the fence and stand the cable real in the summerhouse, now plug in 2x 4 gang sockers and 2x fan heaters to keep you warm, for light use a inspection light from your garage easy, dont know what all the fuss is about.

locost mate, rcd waste of time just buy a rubber door mat and stand on that.

btw i'm not a spark so only use this advice if you are stupid

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The only acceptable way of terminating SWA is the proper glands designed for the job. How on earth (ha ha punn intended) will you make a proper connection to the armour with choc-block?

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Originally posted by mangogrooveworkshop

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The only acceptable way of terminating SWA is the proper glands designed for the job. How on earth (ha ha punn intended) will you make a proper connection to the armour with choc-block?

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Good call.......Its the poor workmanship / choice of equipment that keeps us in a job...

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I believe the fixed connectors were inside a a waterproof adaptable box, therefore you gland the SWA cable into the box and the use a 'banjo' earth tag under the nut and bolt through then attach an earth cable to it and therefore maintain the earth.

Or you can use a three phase cable and use one of the cores as earth so long as you sleeve it up correctly to identify it.

The regulations now call for RCD's on all circuits which are not protected in a metallic conduit, it is therefore better to use individual one's to stop the lights going out when you trip the power, although there's nothing wrong with putting them all on one.

Here's some pics of an installed banjo, they come with the gland when you buy one.

Image deleted by owner


Image deleted by owner



[Edited on 31/7/10 by big-vee-twin]

Being that I've just passed my 2391 test and inspection, there is a specific regulation (can't quote without my regs book) that it is now a requirement to have individual RCD's (called RCBO's) for each circuit.
You can run any cable that is suitable for the enviroment, so twin and cpc cable is acceptable where it is protected and swa where it is subject to possible damage. The join can be in a non-ip rated box if not in a wet enviroment so it can be inside the house, but must be accessable for maintenance/testing.
You can use a 100mA RCD on the cable to the out-building and 30mA RCBO's on the final circuits. This will provide shock protection in the building and discrimination so you don't lose the complete supply.
Remember that when selecting cable sizes, Length of run (volt drop) Current and installation methods will affect the Cross sectional area of the cable. For instance, if the Twin and cpc cable is run under loft insulation it can dramatically create the need to increase cable size. BS7671 regulations are your friend.
Apart from all that, are you Part P qualified to do the work?
Under Building regulations you need to be or it is a criminal offence with fines of 5K or prison.
You can still install it but would need the Part P installer to test and inspect it before connection.

I can't remember every circuit needing rcbos?!?!

In the 17th it states that now all cicuits need to be rcd protected, ie from a split board with 2 rcds but no requirement for rcbo on every outgoing circuit?

An as for part p, he could always be replacing a length of cable thats already there, so he wouldn't need it, or just altering an existing circuit, so he wouldn't need it etc etc

In domestic buildings all circuits need RCD unless installed within a metalic conduit which is earthed, In a commercial building it is up to the designer to choose.

Many people have nicked through cables in domestic type buildings during construction making the metal frame that supports the plasterboard wall and ceiling, live

The RCD's were introduced to combat this growing issue as I understand it.

I always design lighting on RCBO'S because if a lamp goes you don't loose all your lighting circuits, its optional to have a single RCD or multiple RCBO's.

I just think it makes a better job.



[Edited on 31/7/10 by big-vee-twin]

The regulation is specific to prevention of losing all circuits (discrimination) when covered by a common RCD, so Individual RCBO's required for each circuit.
Regulation 314.2, which requires that a separate circuit be provided for each part of an installation which needs to be separately controlled so that it remains energized in the event of failure of any other circuit of the installation.

And no you cannot work on an existing domestic installation with out Part P or having it checked/tested by someone who is, even if the wiring is a replacement or not.
You are getting confused by non-notification rules. You don't have to inform your local authority if you change the existing cable. My understanding is this is not an existing cable anyway.
Besides, the person doing it must still be "competent"
Competent is defined as Experience, knowledge and training. The fact that the question is being asked shows a lack of knowledge.
Altering an existing installation means it should come up to the latest regs. Something your layman will not know.


[Edited on 31/7/2010 by nitram38]

That isn't a blanket requirement though. You can still install split load CUs with rcd each side and no rcbos if the installation doesn't warrant it. In most homes it will not.

And I don't want to be pedantic but you can still carry out your own non notifiable work without being part p registered. That's the whole point of the notification rules, who can do what and whether part p is applicable to that case.

Linky

Taken from there:

Notifiable work includes new installations, house re-wires, and the installation of new circuits. Notifiable work also includes additions to existing circuits in kitchens, bathrooms, outdoors and in other special locations

[Edited on 31/7/2010 by nitram38]

Agreed this project comes under notifiable work, but non notifiable work can still be completed by the diy'er

BS7671 is a british standard, not a law. Electricians comply with bs7671 because it is a proven way of doing a safe install. If you have complied, then if you end up in court you can prove you worked to best practice. That isnt to say that you cannot choose to do something differently if you are prepared to argue in court that your way was also safe.

Approved document P is merely guidance on complying with the building regs.

I believe the penalties Martin refers to would actually be for dangerous work rather than mere non-notification etc.

The law is a toothless dog anyway:

Correct link

if you can get away with a job that bad.



Regarding OPs question, i would fit a fused 13A connection in the nearest internal room, and run 2.5mm cable in buried conduit. If its wired properly you needn't worry about the RCD tripping, unless you run too many computers at once. Either way, fitting a double pole switch in the house would allow you to isolate the outhouse in the event of a fault.

This would be the cheapest way to get the job done.

You can buy 4mm t&e cable on ebay for £18 for 50m, if you fancy that route.

[Edited on 31/7/10 by JoelP]

Can I just point out that just because somebody asks a question or advice on which option to take (neither, in my opinion was stupid), does not make me incompetent at DIY.

Me moving country to somewhere where the inspection regs are tighter does not immediately turn me into an incapable baboon. I would be more than happy to notify/inspect the notifiable work, but it's absurd to me that it will multiply the cost by several times simply to have someone from the local council give me a thumbs up. Particularly as in some cases I have heard of people getting approval without so much as a test around here. So how am I safer then??


Either way, in order to do it by the book and could you please advise me on what I can do as "prep work" so as to minimise the 100 quid an hour equivalent cost that a spark would charge me?

I.e. I can dig the trench, I can put conduit pipe in it, I can fit the sockets and consumer unit in the shed, etc. Am I okay to run the cable and let the leccy connect it, or will it not be signed off then?


Finally, as a two-fingers-up to them option, if I drill a hole through my kitchen wall, pass a cable through there, terminating into an RCD breaker which simply plugs into one of the kicthen 13amp sockets, and keep the rest of the wiring in the shed the same (i.e. sockets/lights etc.), I can argue that technically it's just an extension cable as I can always unplug it, correct?

quote:

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Originally posted by nitram38
The regulation is specific to prevention of losing all circuits (discrimination) when covered by a common RCD, so Individual RCBO's required for each circuit.
Regulation 314.2, which requires that a separate circuit be provided for each part of an installation which needs to be separately controlled so that it remains energized in the event of failure of any other circuit of the installation.

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