Discuss cavity wall in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net

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kellogs64

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Hi all
Are you still allowed to run cables in a cavity wall to wire a conservetry to conform to 17th edition amedndmant 1
many thanks for your help,if you could direct me to the relevent page in the wiring guides would be even better.
 
M

MarkieSparkie

There is no specific regulation that forbids an installer installing a cable within a cavity wall. However BS 7671:2008+A1:2011 and The Building Regulations:2000+A:2010 highlight a number of reasons why this practice is undesirable:

The cable may be damaged during installation - BS 7671:2008+A1:2011, 522.8.1 refers.

The cable lacks support and also damage may occur due to the cable's own weight - BS 7671:2008+A1:2011, 522.8.4 refers.

Thermoplastic insulated and sheathed cables (PVC/PVC) in contact with polystyrene may cause the plasticizer within the insulation to migrate, leading to softening of the cable sheath - BS 7671:2008+A1:2011, 522.5.3 refers.

Cables installed within thermal insulation will have their current carrying capacity significantly reduced, which may require cable sizes to be increased - BS 7671:2008+A1:2011, 523.9 refers.

The cable may be attacked by flora and fauna - BS 7671:2008+A1:2011, 522.9 refers.

The cable may be in contact with the outer and inner wall thereby providing a route for water - Approved Document C Building Regulations refers.

From above, it is easy to see that cables should not normally be installed in external cavity walls, but where it has to be done the installation designer may well judge that Mineral-Insulated Copper Sheathed (MICS) cable is a suitable choice in such a location providing its selection and erection complies with BS 7671:2008+A1:2011.
 
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M

MarkieSparkie

would running singles through pvc conduit fix it rather than mineral insulated,i dont fancy trying to use swa?
Yeah, that would be fine if your going at right angles, bridging across the cavity, but very difficult to run horizontal or vertical in the cavity.
 

kingeri

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Can't add much to what Markie said (as usual!). I tend to view cavity walls as a no-no unless it's a last resort. If there really is no option then go with armoured!
 

huntos33

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Always do mine in PVC conduit normally drop down in the room the conserveatorys built off drill through and fit a socket and tube from here, or wire back to back off exsiting socket and so on
 
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kellogs64

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Always do mine in PVC conduit normally drop down in the room the conserveatorys built off drill through and fit a socket and tube from here, or wire back to back off exsiting socket and so on
conduit on show ?

want a system thats not on view ie trunking,conduit.theres got to be a more suitable cable than swa or mi ?

how much do you charge to wire a coservatery roughly
 

telectrix

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Surface mount in trunking if you can't channel the wall, or go under floor. Absolutely no way I would run in cavity.
i generally use pvc conduit laid on top of the fibreglass in the cavity of the dwarf walls. no way would a customer allow surface wiring. under floor is only an option if i can get in before the screed is laid.
 

telectrix

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i charge between £250 and £350 for most. that's allowing for 2 visits, 1st/2nd fix.
 

telectrix

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i usually fit 2 twin sockets and a wall light or 2. light/s via a 3A FCU off the circuit feeding the sockets.
 
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kellogs64

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thanks again for your advice

is'nt there a cable you could lay in there,somthing inbetween pvc/pvc and swa

would i be better talking to my wholeseller,surley laying a cable between bricks wouldnt need the protection of swa,after taking into account the other facters
 
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imago

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,surley laying a cable between bricks wouldnt need the protection of swa,after taking into account the other facters
As markiesparkie said in the first reply, Mics.

Taking into account "the other factors" is what results in the need. I can see that you don't want to use mics or swa, but if you want to run the cable through the cavity that's what you need.
 

Richard Burns

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is'nt there a cable you could lay in there,somthing inbetween pvc/pvc and swa
Cables between T&E and SWA are Hituff, multi flex SY control cable, NYYJ cable or possibly FP cable but this is not really a solution to the problem if you read post#2 there are other factors at work.


EDIT too slow: as imago said!
 
E

Engineer54

Can't see a problem myself, conservatory walls are normally only around 500mm (or less) high before the glass starts. So given that the cable has been sized appropriately for insulation de-ratings etc, i wouldn't have a problem running cables in the cavity of a conservatory, .... for my own property at least...lol!!.
 
E

Engineer54

Thermoplastic insulated and sheathed cables (PVC/PVC) in contact with polystyrene may cause the plasticizer within the insulation to migrate, leading to softening of the cable sheath - BS 7671:2008+A1:2011, 522.5.3 refers.
Not anymore, not since the 80's


The cable may be attacked by flora and fauna - BS 7671:2008+A1:2011, 522.9 refers.
Surely that's true of any installation location...


The cable may be in contact with the outer and inner wall thereby providing a route for water - Approved Document C Building Regulations refers.
The times i've heard this nonsense!! So what are the ties doing then?? Let alone the dollops of mortar that gets dropped in/down the cavity of just about every brick/block built building ever constructed... Or even, what about the insulation sheets come to that??

Not saying that i would advise anyone to run cables in the cavity in normal circumstances, but when you have very low walls, as you find in most conservatory's, in all reality, it's not going to create any real problems at all....


 
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kellogs64

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the way i read it is flex with a steel reienforced(sorry not sure what its called) should be more than adequate,as for the rest correction facter is .5 when run through insulation over 500mm even 2.5 on a fused spur would do it
 

telectrix

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i have to say that a few times, i've run T/E in the dwarf wall, sitting atop the insulation. it's supported: current demand is very low, so derating is no problem; it won't get damaged as the only work being done near it is fixing the pvc frames. can't see a problem. and if rats etc. do get to it. then it's been badly built in the first place.
 
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kellogs64

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I sort of agree , but I would rather have a bit more protection than just PVC/pvc . Agree with demand,the most your gona to have is a tv + dvd player and a table lamp,will always ask just in case he wants to weld in his conservitry lol
 
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Guest55

totally agree with Eng54 , glad someone has at last given a real world view.
i dont see why pyro or swa is suggested as the only appropriate cable types for sticking in a cavity ??
none of their unique properties are needed for a few metres inbetween walls.
its probably the most impact and fire free area of any property.
and as for transmitting damp between the 2 skins , lol , no chance.
 

telectrix

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just need to make sure that you evict the cable munching fairies from the cavity first.
 

imago

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So what are the ties doing then?? Let alone the dollops of mortar that gets dropped in/down the cavity of just about every brick/block built building ever constructed... Or even, what about the insulation sheets come to that??
The ties should slope from the inner leaf of the wall to the outer to wick moisture to the outside. They should also have 'drip bends' in them to cause the moisture to bead up and drop.

There shouldn't be any dollops of mortar in the cavity as the inner faces of the brick and block should be cleared as each course goes up.

The insulation sheets should be held to the inner leaf of the wall using plastic clips over the ties. This prevents bridging and allows air movement in the cavity to reduce condensation.

All this of course is according to the building regs, but I suppose any of the trades can choose which bits they want to follow and which they don't?
 
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kellogs64

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If the regs state it why not implement it rather than going against the grain,not saying I would use swa or mi that's going too far , sling in a bit of conduit happy days or a lesser version of swa sorted jobs a good one
 
E

Engineer54

The ties should slope from the inner leaf of the wall to the outer to wick moisture to the outside. They should also have 'drip bends' in them to cause the moisture to bead up and drop.

There shouldn't be any dollops of mortar in the cavity as the inner faces of the brick and block should be cleared as each course goes up.

The insulation sheets should be held to the inner leaf of the wall using plastic clips over the ties. This prevents bridging and allows air movement in the cavity to reduce condensation.

All this of course is according to the building regs, but I suppose any of the trades can choose which bits they want to follow and which they don't?
I think we both know, as well as everyone else, that none of these things are adhered too!! 50% of those wall ties would be installed upside down anyway. You can't really avoid dropping mortar between the courses, you can only clear some of it as you go. Haha, never seen any clips holding those insulation sheets to the inner wall. So how do they hold the insulation balls and flakes in place then, that can be retro injected into these cavities spaces??
 

imago

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Absolutely, I doubt you'd find 5% of walls built to the regs in those respects. However they are the regs, and by running cables along the cavity either vertically or horizontally the regs wouldn't be followed for that reason.

It's one of those areas where common sense applies. So for example the cable running through at the top of a dwarf wall 500 -600mm high would cause no more issues than the lower face of the timber or plastic which closes the top of the cavity.

My point being ignorance of the regs, or ignoring the regs, is unacceptable. Choosing an unusual method is perfectly acceptable as long as the person doing so knows why a specific reg has the requirements that it does, and that their chosen departure/alternative can be shown to be as effective or better.

Balls, flakes, fibres and foams aren't covered by the current regs other than to exclude them from use when building to current regs.
 

telectrix

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compared to 50 years ago, houses today are thrown up. they may be built to hold a bit more precious heat inside, but i challenge you to come up with 0ne improvement other than that, over a hose built entirely with bricks and real wood (none of this thermalite dust crap, and chipboard, mdf, roof trusses that totally bar access to lofts, dry lining cardboard that won't take a fixing........ etc.etc.
 

imago

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I accept the challenge :)

Cinder blocks which were used prolifically in the '40s '50s and '60s are no longer allowed. They were just as crumbly as the modern thermal blocks, and they also started to burn if the building caught fire because they were essentially compressed cinders from the coking plants.
 

imago

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Challenge aside, I do agree with you. Modern construction techniques mean that buildings have built in obsolescense, and I don't think thermal efficiency is the reason. If a building lasts for a hundred years it's bad for all the industries involved in putting it up. If it lasts for thirty or so there is a turn around which keeps everyone in business/work.
 
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Engineer54

I accept the challenge :)

Cinder blocks which were used prolifically in the '40s '50s and '60s are no longer allowed. They were just as crumbly as the modern thermal blocks, and they also started to burn if the building caught fire because they were essentially compressed cinders from the coking plants.
I bet those houses built with those cinder blocks will outlast anything built from the 70's onwards. Most of the council houses, and probably the low rise flats were built with them. Those in my parents house (built in 51) where i grew up, were pretty dam solid, as were the bricks that were used...
 

imago

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I bet those houses built with those cinder blocks will outlast anything built from the 70's onwards. Most of the council houses, and probably the low rise flats were built with them. Those in my parents house (built in 51) where i grew up, were pretty dam solid, as were the bricks that were used...
Which is just like saying that an old rewireable fuse board will outlast a modern board. It's true, but misses the point.
 

Guitarist

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I sort of agree , but I would rather have a bit more protection than just PVC/pvc . Agree with demand,the most your gona to have is a tv + dvd player and a table lamp,will always ask just in case he wants to weld in his conservitry lol
I know several people who don't have central heating in their conservatory, just plug in a 3kw fan heater when it gets cold.
 
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