Cavity wall wiring

[sirocco]

I have a single story building and need to run a cable for outside lighting on a patio from a feed in the roof/fascia area.
The most direct route would be down via the external cavity wall (2.5M run length in the cavity) which has full fill rockwall insulation (100mm thick). I am intending to use 2.5mm NYY-J cable which is RCD protected.
Is running in a cavity an absolute "no no" or is just not advisable under the 17th edition regs?

 

[KINKY]

Nothing wrong with it as long as you pay attention to the de-rating factor imposed by the insulation.

 

[marksparky]

its a no im afraid! thats not to say people dnt do it, was a job today puttin extra socket in sunroom and the socket i intended to spur off was fed by the two legs of the ring both comin down the cavity

 

[telectrix]

and make sure the cable can't chafe on the masonry. only thing wrong is the cable is not supported adequately, ( forgot which reg.). could you feed it in copex?

 

[rocker]

These aren't the only issues. If the cavity is re-insualted with standard cavity isulation i.e. poly balls, then the polystyrene will cause the plasticiser in the pvc insulation to migrate into the polyballs and the insulation will become brittle and crack.

 

[SirKit Breaker]

Would SY cable do the job?

 

[Coffeemad]

Knowing how some cavities are generally full of "stuff", the shennigans of fishing through 4inches of brick into a cavity of a 2.5m of wall, would it not be easier to run the cable outside, in some black plastic conduit? That gets around all the de-rating factors, protection of the cable from drilling by others and chemical reactions.

Its generally my prefered choice, especially if there is already other external guttering, soil pipes, sky dishes etc

 

[sirocco]

The big advantage I am trying to gain is that the building is currently under construction and the cavity is accessable from the side which is open for the full height. No fishing or anything like it just , push the cable in from the side and bring it out above the brickwork at the top and through a hole in the brickwork below. When the door frame is fitted the cavity side with be closed off.
I estimate it to be a 15 min job.!

 

[sythai]

If that the case... stick it in a length of plastic copex and you will be fine