Cables in wall cavities

[Doomed]

I was bored the other day and e-mailed the IET advice line on thier view of cables run in cavities.
Here is thier answer:

Hi *****


I am required to preface my remarks by saying that I have no authority to interpret the requirements of BS 7671:2008, Requirements for Electrical Installations.
The interpretation of BS 7671 is one of the roles of the Joint BSI/IEE Committee JPEL/64. However, within that constraint, I hope you will find my comments helpful.
Cables should be chosen and installed taking into consideration the environmental factors present. If a cable is chosen to overcome the factors present within a cavity wall,or the future possibilities, then a cable designed or by design capable of with standing these factors can be used, although I would not recommend it and would consider it extremley bad practice and poor workmanship. The case for proper cable support must also be adressed, how would you clip or support a cable properly in a cavity?. The only cable system with remotely advantageous environmental characteristics , in my mind, would be MICC. However the supporting containment for this must be installed in accordance with the regulations.
In short, if you find a cable that can withstand the environmental influences , you would’nt be able to satisfy the regulations for the support of cables. To that end you can’t put cables in cavities , mainly because they can’t be supported adequatly.

Cables traversing the cavity (for outside lights and sockets for example, should theretically be suitable for the environment at that point or protected from it (possibly using an insulated conduit ).

The general answer is No you can’t , unless your thin enough to slide down the cavity and clip the cable( of the correct type and in this case I feel that is MICC) to the inside of the cavity.
I hope this helps

I hope these comments are usefull to you

Many Thanks
*******

 

[bugsy]

Just about sum's it up

 

[ezzzekiel]

"The general answer is No you can’t , unless your thin enough to slide down the cavity and clip the cable"

sounds like a bit of a c!"k to me

 

[telectrix]

last week i had to install 2 sockets in a conservatory. only way to get cables to the sockets was through the cavity before the plastic was installed. reason being , the brickwork was being left as bare brick and client would not allow trunking. at least the cable is supported after a fashion sitting in the cavity ties. anyone on here come up with a better way, let's hear it!

 

[ringer]

last week i had to install 2 sockets in a conservatory. only way to get cables to the sockets was through the cavity before the plastic was installed. reason being , the brickwork was being left as bare brick and client would not allow trunking. at least the cable is supported after a fashion sitting in the cavity ties. anyone on here come up with a better way, let's hear it!

If this was before the windows were installed, were you then able to look down into the cavity? If so, would it not have been possible (difficult but not impossible) to clip direct? Alternatively, run the cables in plastic conduit in the cavity and rest the conduit on the ties instead of the cable resting on the ties. Another advantage of that method would be if ever the cable needed to be replaced, it might be then possible to do so with the conduit guiding the cable routing.

As for the comments about the IET guy's response, I thought that what he replied was quite a human (and mildly humorous) response - much better than just quoting regulations.

 

[Deleted member 9648]

Another issue is future insulation in the cavity....but the IET guy's points are all 'academic' really....cables have been run in cavities for donkey's years without any problems from percieved lack of support,if anyone can show me a cable which has been damaged by laying in a cavity I would be very surprised....but you have to tow the line I guess.

 

[johnboy6083]

its only as bad as cables in new flats, with the plasterboard walls and the metal support track. cables clipped to concrete above ceiling, and then hung behind plasterboard to sockets switches ect.

 

[Spudnik]

Has anyone ever seen a cable damaged by its own weight?

 

[Des 56]

Well theres political correctness,where its difficult to rebuke an argument,but we know its nonesense
and in this instance there is Iet correctness,you cant argue against his points,but in the real world,they dont hold sway
As he said he was interpreting what the regs meant,more as an individual,"--- covering" more like,because they dont commit to thou shallt do as I say
The regs are smokescreens that we try to see through
Cavities.nothing much wrong with that method,but you wont ever catch me doing that (whispers lies again )

 

[accordfire]

Has anyone ever seen a cable damaged by its own weight?

Well, being pedantic, I have seen them pulled out of junctions by their own weight (with a bit of help from a fire collapsing an allegedly fire proofed wall)...

Arguably, a length of conduit should be thin enough to slide down the cavity though.......and would be environmentally suitable, and relatively stable if saddled top and bottom.

More to the point though - has anyone EVER seen an inspector thin enough to slide down the f'ing cavity to make sure you DID clip the cable?

That, to my mind, was an answer given by some spotty little nerd, who's never, ever seen the business end of the trade in his short trousered little life.

But at least those short trousers have covered his baby smooth behind adequately.

 

[drew35]

Isn't there something about not running cables in the cavity because of moisture transmission between the outer and inner skin? I'm sure I've read it somewhere, probably on a post here.

 

[1shortcircuit]

Did the outer sheathing of the cable use to react with a particular type of cavity insulation giving off harmful gasses?

 

[accordfire]

Isn't there something about not running cables in the cavity because of moisture transmission between the outer and inner skin? I'm sure I've read it somewhere, probably on a post here.

The point of the cavity is to act as a barrier between outside and inside - warm interior walls and cold exterior walls, it is probably going to end up fairly changeable in temperature.

It seems reasonable that the insulation of a cable will suffer more here than surface run - but wouldn't this apply to cables run under floors in the footings as well? And in lofts?