Electric Cables in Cavity Walls

[Davey]

Not a problem so much as an enquiry...

In a recent post it was stated that cable must not be run in exterior cavity walls as it could be dangerous because of damp and possible wall insulation problems.

I live in a modern (1980's) purpose built flat which has several sockets located in the exterior walls. The floor is concrete and the cables are run down the walls from the loft space above (I am in the top floor flat). The cables are run loose in the cavity - i.e. not in conduit and the walls are insulated with the same material used to insulate lofts (fibreglass???). Is this safe?

I would also like to extend the ringmain in the kitchen to accomodate two extra sockets over a worktop but the layout of the kitchen means that these will need to be located in another exterior wall. Is this allowed by the regulations and (more importantly) is it safe?

Any advice would be much appreciated.

 

[ban-all-sheds]

The restriction on running cables in cavities is becuse the foam insulation sometimes used will leach the plasticiser from the PVC sheath. The fact that your insulation is fibreglass is irrelevant - someone in the future might remove that and pump foam in, so you might have problems in running your new cables through the cavity.

Also, significant de-rating has to be done when cables are enclosed in thermal insulation, and extending the length might upset the calculations already done.

How feasible would it be to chase a channel in the wall for the new run? Could you have the majority of the new cable clipped to the wall under the worktop, and therefore out of sight, with just a short bit of chasing to do to run up to each socket?

Another alternative you might consider, if it doesn't clash with the decor style of your kitchen, is installing dado trunking on the walls directly under the wall cupboards

 

[nstreet]

In my last house the cavity was insulated with polystyrene beads. When we had the utility room demolished to make way for a new extension, we discovered that the cables from the c/u were run in the cavity. The grey sheathing had turned into a substance resembling soft chewing gum, where it had been in contact with the insulation.

 

[Davey]

Thank you for your replies - I now understand the reason behind the restriction.

The new sockets in the kitchen will be installed within 2 metres of an existing socket so the increase in the cable length will be minimal. Surely this short distance would have a negligible effect on the current carrying capacity of the cable?

The wall is made of plasterboard with a thin skim of plaster over it and this is then tiled. Is it possible to chase out this wall to accomodate the new cable and, if so, what is the best way to do this?

Underneath the worksurface are a built in fridge and freezer. Would it be acceptable to clip the new cable to the wall behind these as they do generate some heat?

I would consider dado trunking as a last option (as the new sockets are desperately needed!!!) but would prefer to have the cable completely hidden if at all possible.

Thanks once again for your help and advice.

 

[ban-all-sheds]

The new sockets in the kitchen will be installed within 2 metres of an existing socket so the increase in the cable length will be minimal. Surely this short distance would have a negligible effect on the current carrying capacity of the cable?

Shouldn't be a problem - my only concern was if you added a long run of thermally insulated cable to a circuit where the effects of insulation had not been considered then you might have problems, but an extra 2m is not going to be a problem - put it this way, if it is, then you already have problems!

The wall is made of plasterboard with a thin skim of plaster over it and this is then tiled. Is it possible to chase out this wall to accomodate the new cable and, if so, what is the best way to do this?

Before tiling would be best What's behind the plasterboard? Is it glued to the wall or fixed to battens?

Underneath the worksurface are a built in fridge and freezer. Would it be acceptable to clip the new cable to the wall behind these as they do generate some heat?

I very much doubt that they generate enough heat to upset the environment of the cables.

I would consider dado trunking as a last option (as the new sockets are desperately needed!!!) but would prefer to have the cable completely hidden if at all possible.

They do a good job of hiding the cables:

(imagine them mounted upside down, so that the square edge butts up against the underside of the wall units and the curved or chamfered edge is at the bottom). Provided you can get the cables into one end without them showing then, IMHO, they don't look too bad. Not as good, of course, as properly buried cables and flush accessories, but often a lot easier and less damaging to existing decor, and, of course, its very easy to add new sockets or switches if you ever need to.

 

[nstreet]

I used some Marshall Tuflex dado trunking in a kitchen refit, brilliant stuff. Saves a lot of hard work. The down side though is its very costly if you have to buy it. I managed to obtain mine from an office that was being refurbished.

 

[nigelsz]

if you cables are in cavities and you are worried , as you should be if you believe the coontributors to your query (and i wouldnt argue with their expertise )
You should be able to pass conduit over your cables retrospectivly if you lucky and you can trace you runs ............. cavity insulation if it foam type is easily pushed through better than exp chewing gum sheathing .
I would alway try to play safe when it comes to anything in the home .if you know something aint quite right try to put it right

hope this is helpful