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Running cables behind plasterboard walls


 
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inigopete

from United Kingdom

Joined: 19 Feb 2008
Posts: 8
Location: London,
United Kingdom

PostPosted: Tue Feb 19, 2008 7:37 pm Reply with quote

Hi,

I admit that this is my first post and it's a real newbie question, for which I'm sorry; if my question is easily answered by an FAQ or other post, please point me towards it. I've had a couple of quick searches and short of downloading Part P and digesting all of it I can't find a simple answer...

I'm fitting a cooker hood above a hob. It will be fitted to a plasterboard wall, that I've just cut a section out of to fit the flex outlet. I'll be running a spur via a fused isolator from the cooker loop - both hob and oven are gas-powered so the only things actually powered by electricity are the igniter sparks and the oven clock.

I'm planning on running the cable up the wall vertically from the socket, then a horizontal run across, then a vertical run a few inches down to the flex outlet.

I've just cut the first square out of the wall to fit the mounting box for the flex outlet and found that the wall is basically two plasterboard sheets about 50mm apart (the bathroom is on the other side of the wall). There is very little between the two boards and the board itself is only about 10mm thick.

My question is: do I need to enclose the mains cable in plastic ducting, and if so, how do you suggest fixing it within / behind the boards, or is it acceptable to simply leave the cable loose in the space, still observing the vertical and horizontal runs?

Any advice / scorn would be appreciated!

Thanks,

: P
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luminaire

from United Kingdom

Joined: 11 Jan 2007
Posts: 704
Location: United Kingdom
Thanked: 1 time

PostPosted: Tue Feb 19, 2008 7:42 pm Reply with quote

Wouldn't it have been easier to spur off your lighting circuit from above?
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inigopete

from United Kingdom

Joined: 19 Feb 2008
Posts: 8
Location: London,
United Kingdom

PostPosted: Tue Feb 19, 2008 7:45 pm Reply with quote

I'm in a ground floor flat so I don't have easy access to the lighting circuit without tearing out bits of ceiling.

: P
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ban-all-sheds

from United Kingdom

Joined: 27 Aug 2003
Posts: 47631
Location: London,
United Kingdom
Thanked: 1759 times

PostPosted: Wed Feb 20, 2008 12:16 am Reply with quote

inigopete wrote:
I've had a couple of quick searches and short of downloading Part P and digesting all of it I can't find a simple answer...

1) Part P is a Building Regulation- it won't give you info like this, you need a copy of the wiring regulations and/or a guide to them, the On-Site Guide etc.

2) But assuming it were to, as you think it does, why aren't you prepared to put the effort into digesting it?

Quote:
I'm planning on running the cable up the wall vertically from the socket, then a horizontal run across, then a vertical run a few inches down to the flex outlet.

No - not allowed - that is not the way that concealed cable zones work - you can go horizontally or vertically from accessories, you can't put in doglegs.

Quote:
I've just cut the first square out of the wall to fit the mounting box for the flex outlet and found that the wall is basically two plasterboard sheets about 50mm apart (the bathroom is on the other side of the wall). There is very little between the two boards and the board itself is only about 10mm thick.

So your problem gets harder - even if you didn't need a dogleg, it sounds as though the position of the accessories, and therefore the cables, could not be determined from the bathroom, so that's another non-compliance.

Quote:
My question is: do I need to enclose the mains cable in plastic ducting,

No - you need to enclose it in earthed metal conduit. Or use armoured, MICC or split-concentric cable.

Read these:

http://www.voltimum.co.uk/files/gb/attachments/niu/l/attachments/c5-43.pdf

http://rapidshare.com/files/82671380/concealedcables.pdf

IEE Wiring Matters Issue 14

BTW - this is not some technical "ideally you should, but..." point - people have died as a result of the sort of dangerous cable routing you plan.


Quote:
Any advice / scorn would be appreciated!

Good job you asked, or when LABC came after first fix to inspect it, they'd have failed it....
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inigopete

from United Kingdom

Joined: 19 Feb 2008
Posts: 8
Location: London,
United Kingdom

PostPosted: Wed Feb 20, 2008 9:15 am Reply with quote

Thanks for taking the time to reply, ban-all-sheds, and for the reading matter.

I probably should have made a couple of things clearer in my FP:

- Although the bathroom is on the other side of the wall and you can't see both sides of the wall at once, the bathroom door is only a couple of inches in from the edge of the wall and it's pretty easy to correlate fittings on one side of the wall to the other side.

- I was planning to run the cable vertically up from the cooker switches to just under the ceiling, keeping the horizontal run well within the 150mm zone across the top of the wall, then vertically down a short distance more to a high-level flex outlet point. As I understand it, that doesn't seem to contravene the regulations you pointed me to.

However, my choice of cable looks like it's wrong. If I do it as above and use split-concentric cable, would that be OK? And, if so, is it generally better practice to leave the cable loose in the space or would it be better to either tape it to the back side of the plasterboard (or use my aforementioned plastic ducting): I was thinking that a loose cable would be harder to hit by a future stray nail or screw, but a cable close to the surface of the board would be easier to detect with a stud/voltage detector.

Thanks again,


: P
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cleverspark

from United Kingdom

Joined: 27 Nov 2006
Posts: 84
Location: South Tyneside,
United Kingdom

PostPosted: Wed Feb 20, 2008 9:45 am Reply with quote

im just giving my thoughts on this but have to mention that I am not 100% so please don't take my answer as gospel.

From what I think as long as you run vertically or horizontally from the switch and then into the 150mm zone at the top where you wish to run horizontal, this seems to me that it will be more then staisfactory and meet the regulations.

The main concern I have is that since it seems to be two plaster boards backed onto one another, how are you going to support the cable at the top of the room, how will you prevent the cable from dropping from the new installed socket to the original socket and therefore not sticking to the safe routes? This is my concern.

From what i read that if you have a partition wall then it is upto the electrician or whomever to ensure that there is no electrical fixings on the opposite wall, the zones basically coming thru the entire wall.

Of course, one method of making sure it is 100% compliant is by placing the cable in earthed conduit. Now that would take some doing without ripping a wall to bits icon_lol.gif
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