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Topic Title: Internal Cavity wall
Topic Summary: Am I allowed to use it ?
Created On: 25 February 2010 06:33 PM
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 25 February 2010 06:33 PM
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Ampman

Posts: 988
Joined: 06 February 2006

Evening ,

Carrying out a rewire this week , The old cables are fed through a internal cavity wall into the DB ,

Can I use the same route ?

Mains tails will be surface .

cheers
 25 February 2010 06:39 PM
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misterben

Posts: 415
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Why do ou think you wouldnt be able to?

regards

Misterben
 25 February 2010 06:42 PM
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Ampman

Posts: 988
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Thought I read some where cables in cavitys a big no no ?
 25 February 2010 06:46 PM
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misterben

Posts: 415
Joined: 11 June 2007

cables less than 50mm in a wall? within safe zones?


regards

Misterben
 25 February 2010 06:55 PM
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sparkiemike

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Guidance from the Electricity Safety Council says "installing such cables in this way (external cavity walls) is generally an undesirable practice"

The reasons give are
1. Obstructions in a cavity wall, such create a risk of unseen damage during installation.
2. Long unsupported vertical drops may place undue strain on the conductors, leading to damage
3. Polystyrene used for insulation, if it come into contact with thermoplastic (pvc) cable sheathing, plasticiser can migrate from the thermoplastic to the polystyrene
4. Thermal insulation in the cavity may cause cable not to be able to carry the load current without overheating due to their current-carrying capacity being reduced
5. Presence of flora and fauna - unforeseen external influences

There is also a requirement in the Building Regulations 2000, Approved Document C, 2004 Edition, Section 5: Walls, paragraph 5.13 b
and NHBC Standards state that no cables other than electricity meter tails are to be located in the cavity of an external wall
 25 February 2010 07:02 PM
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Ampman

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Its a drop of about half a meter

I will have to chop the lounge wall out then i suppose Go back entry that way .
 25 February 2010 07:03 PM
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misterben

Posts: 415
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I think ampman is talking about a few feet of cable routing throught to a DB?
I had to move a DB and dropped cabling about two feet from ceiling into cavity directly into DB. The customer wouldnt want surface trunking or their wall chopped out. As for the derating issue that has been raised before i.e cable covered in insulating foam; is this first few feet of a 30-40 feet run going to really affect the cables current carrying capacity? I think not

regards

Misterben
 25 February 2010 07:06 PM
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Ampman

Posts: 988
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Cheers Misterben ,

Didnt think of it like that its only a drop of a few feet from upstairs underfloor boards into DB located within the porch .

I will carry on now

Thanks
 25 February 2010 07:08 PM
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misterben

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Originally posted by: sparkiemike

Guidance from the Electricity Safety Council says "installing such cables in this way (external cavity walls) is generally an undesirable practice"



The reasons give are

1. Obstructions in a cavity wall, such create a risk of unseen damage during installation. - dont we test for these before we energize?
2. Long unsupported vertical drops may place undue strain on the
conductors, leading to damage - agree with this, but for a metre ?

3. Polystyrene used for insulation, if it come into contact with thermoplastic (pvc) cable sheathing, plasticiser can migrate from the thermoplastic to the polystyrene

4. Thermal insulation in the cavity may cause cable not to be able to carry the load current without overheating due to their current-carrying capacity being reduced- as i said above

5. Presence of flora and fauna - unforeseen external influences



There is also a requirement in the Building Regulations 2000, Approved Document C, 2004 Edition, Section 5: Walls, paragraph 5.13 b

and NHBC Standards state that no cables other than electricity meter tails are to be located in the cavity of an external wall


It all seems like another way of making electricians lifes difficult, half of the rules now that were supposed to implement are way over the top in my opinion

regards

Misterben
 25 February 2010 07:18 PM
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daveparry1

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and NHBC Standards state that no cables other than electricity meter tails are to be located in the cavity of an external wall
-------------------------------------------
But the OP isn't building a new house so what have they got to do with it?
Dave.
 25 February 2010 07:29 PM
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misterben

Posts: 415
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Correct, just seems like another example of people forgetting their basic electrical theory and or allowing it to be clouded by too many misguided opinions and the big red book


regards

Misterben
 25 February 2010 07:36 PM
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sparkiemike

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I was simply quoting the ESC guidance, the OP is better informed and can take from it what it wants, alternatively he could read Alan Lynch's book "the part P doctor", Alan pretty much refutes all the the claims and is OK with cables in external cavity walls.

Its only guidance the OP will need to make his own mind up.
 25 February 2010 10:19 PM
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TeesdaleSpark

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Are you talking about a cavity between the exterior wall and the interior wall or a cavity to an internal wall?

Do not install cables within external cavity walls. The cavity is there for a reason and its not for running cables.
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