PSpirine
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| posted on 30/7/10 at 08:32 PM |
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More building (wiring) help
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
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scottfraser
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| posted on 30/7/10 at 08:40 PM |
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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!
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big-vee-twin
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| posted on 30/7/10 at 08:43 PM |
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Hi I am a sparky and would do option2 like he says above
Duratec Engine is fitted, MS2 Extra V3 is assembled and tested, engine running, car now built. IVA passed 26/02/2016
http://www.triangleltd.com
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YQUSTA
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| posted on 30/7/10 at 08:56 PM |
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I would go for 4mm not 2.5 because of the lenght of run and the fact the cable will go underground.
"If in doubt flat out"
Colin McRae
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Liam
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| posted on 30/7/10 at 09:14 PM |
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quote:
Originally posted by big-vee-twin
Hi I am a sparky and would do option2 like he says above
You're a sparky, and you'd terminate SWA with choc-block, and fit 2 RCDs in the 'garage' CU? 
OP - ask in the electrical section here while you're still alive! People there know what
they're talking about. 
[Edited on 30/7/10 by Liam]
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big-vee-twin
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| posted on 30/7/10 at 09:29 PM |
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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?
Duratec Engine is fitted, MS2 Extra V3 is assembled and tested, engine running, car now built. IVA passed 26/02/2016
http://www.triangleltd.com
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Liam
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| posted on 30/7/10 at 10:32 PM |
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quote:
Originally posted by big-vee-twin
Well why dont you offer up a solution?
Thing is, I know I don't know quite enough about the specific requirements for running a supply to an outbuilding, exporting earths etc to just
'offer up a solution' that would be safe and compliant. That's why I advised the OP to go somewhere I know he will get the proper
advice from pro sparks who know what they're talking about. It's not what you know - it's who
quote:
And tell me why using RCD's is dangerous and why using fixed connectors inside an adaptable box is dangerous too?
I never said RCDs were dangerous. I was just questioning the suggestion to fit 2 in the mini CU. Scottfraser probably meant 2 MCBs though. 1 RCD would
be sufficient to protect 2 MCBs in a single room building with 2 circuits. Nothing wrong with using 2 RCBOs though I suppose.
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?
[Edited on 30/7/10 by Liam]
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graememk
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| posted on 30/7/10 at 10:56 PM |
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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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mangogrooveworkshop
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| posted on 30/7/10 at 11:29 PM |
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quote:
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?
Good call.......Its the poor workmanship / choice of equipment that keeps us in a job...
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Ninehigh
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| posted on 31/7/10 at 06:06 AM |
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quote:
Originally posted by mangogrooveworkshop
quote:
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?
Good call.......Its the poor workmanship / choice of equipment that keeps us in a job...
Are you a doctor?
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big-vee-twin
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| posted on 31/7/10 at 07:20 AM |
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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]
Duratec Engine is fitted, MS2 Extra V3 is assembled and tested, engine running, car now built. IVA passed 26/02/2016
http://www.triangleltd.com
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nitram38
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| posted on 31/7/10 at 07:53 AM |
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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.
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Stott
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| posted on 31/7/10 at 09:12 AM |
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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
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big-vee-twin
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| posted on 31/7/10 at 11:54 AM |
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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]
Duratec Engine is fitted, MS2 Extra V3 is assembled and tested, engine running, car now built. IVA passed 26/02/2016
http://www.triangleltd.com
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nitram38
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| posted on 31/7/10 at 01:50 PM |
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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]
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Stott
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| posted on 31/7/10 at 03:43 PM |
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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.
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nitram38
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| posted on 31/7/10 at 06:57 PM |
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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]
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Stott
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| posted on 31/7/10 at 08:55 PM |
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Agreed this project comes under notifiable work, but non notifiable work can still be completed by the diy'er
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JoelP
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| posted on 31/7/10 at 08:55 PM |
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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]
Beware! Bourettes is binfectious.
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PSpirine
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| posted on 1/8/10 at 09:12 PM |
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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?
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Liam
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| posted on 2/8/10 at 10:56 AM |
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quote:
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.
You're a couple of years late for the 314 debate . 17th came out in 2008, meanwhile the entire industry has pretty much agreed on an
interpretation of that poorly worded reg that a mimimum of 2 RCDs in an installation will comply. I take it your 2391 teacher is one of those still
shouting from the rooftops that the dual RCD CUs being sold by everyone as '17th' CUs and being fitted in 99.9% of new installations
cannot possibly comply. Anyway, try the iet forum if you want to ressurect that one .
OP - there's nothing wrong in concept with either of your proposals, but it's the details that make the difference between something safe
and compliant, and something potentially dangerous.
If you were going to spur off your RCD'd kitchen socket circuit, putting another RCD in the shed would not ensure that one trips first - with
two 30ma RCDs in series, which trips first is a lottery, so if your underground cable installation/termination isn't perfect or a fault occurs
in the shed, be prepared to loose your kitchen circuit (including fridge/freezer?). Also, as you say you are limited to 13A so there goes future
expansion. Are you sure you'll never want a heater in there for winter, for example.
Far better to run a new circuit as suggested. Ideally you'd want to keep the cable off an RCD until the shed and give RCD protection there so
you can reset without going to the house. Big-vee-twin mentioned RCD protection required on all circuits unless installed in earthed metal conduit,
but that only applies to cables concealed in a wall (i.e. burried in plaster) less than 50mm deep. So you can avoid the requirement for RCD protection
of your outside supply cable by installing it appropriately - in surface trunking on walls, in the loft it's fine (make sure it isn't
burried in insulation though), or just make it SWA for its entire length.
Sounds like Joelp is suggesting just using t&e all the way. You can bury t&e outside but it would have to be in earthed galvanised steel
conduit. Easier and cheaper to just use SWA. You also dont neccessarily have to bury it - clipped round a wall is OK.
You can do all the work yourself, but as it's notifiable work you legally have to submit a building notice. LABC fees vary and may be around
£200, plus extra for the testing which they'll either do themselves or sub out. Not so bad if you're doing a full rewire with a renovation
(like I've done), but for what you're doing or even smaller notifiable work, the fees are a joke and it's often cheaper just to get
a registered spark. Cheapest option for you would be to find a spark who's prepared to let you do most of the donkey work, then finish and sign
off the lot. Find this spark before you start burrying cables underground etc, as he will want to see what he's putting his name to. And
no - a lead with a plug on one end, and a fixed shed used as an office/studio on the other end does not constitute an extension lead!
Of course, the extent to which you obey the law/rules is entirely up to you, and the buck stops at you if anything goes wrong when you've
decided to ignore the law, and you will get the hassle/cost at house selling time. You're adult enough to make your own decision. Could you be
sure an issue that may never even occur to you wont make your untested DIY install potentially lethal? Would you put two fingers up to the rule-makers
and 'have a go' at doing your own gas work? Structural alterations? Brain surgery? As I said at the end of the day it's up to you,
and the safety of you and your family is in your hands.
[Edited on 2/8/10 by Liam]
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