Running Cables in a Cavity

LED Lighting · May 27, 2014

Is it allowed under BS7671 to run cables into a cavity, if it is allowed is there any thing you need to be aware of? or do?

uksparks · May 27, 2014

Yes you can run cables in cavities so long as its in a proper containment and supported throughout its length. Although not the best thing to do, sometimes it is the only option.

I have run cables in cavities, firstly I put a 50mm pipe, well five of them actually up from the garage to the first floor (about 3 ft) then cemented them into the wall neatly to mount the board on top.

You should not just run / drop cables into cavities as you do not know what is going to come into contact with it, for example falling brick debris, blown poly insulation which will react with the PVC on the cable. So basically just make sure its in some form of ducting on its own away from damage.

Don't forget grouping factors though if you are bunching a load of cables together, but then again it depends how long a distance it is.

telectrix · May 27, 2014

even in pipe though, cables are not properly supported.

Risteard · May 27, 2014

Never mind whether it is permitted by BS 7671. The Building Regulations might be more relevant.

Aside from causing mechanical damage to the cable there is the danger of bridging the cavity.

telectrix · May 27, 2014

cavity is already bridged by wall ties and whatever crap the builder has chucked in.

uksparks · May 27, 2014

See the pics below to see what I did, like I say, that's 50mm pipe, it was a pig and a half getting it in the cavity though. Oh i got the pipe from the garden center. The holes in the joists were already there by the way, i didn't drill them like that!

[ElectriciansForums.net] Running Cables in a Cavity

uksparks · May 27, 2014

telectrix said:
even in pipe though, cables are not properly supported.

I agree, I would only do it if it was a couple of feet like in my photos, anything more and its not supported particularly well.

uksparks · May 27, 2014

telectrix said:
cavity is already bridged by wall ties and whatever crap the builder has chucked in.

Yes indeed, personally I wouldn't worry too much about bridging the cavity as like you say there's all the other crap and insulation in there anyway. You have to do whats best for the job, if its the only way that's practical, then you do it.

Pete999 · May 27, 2014

Used to run cables in the cavity on all new builds to get away from chasing in, back in the good old days late 60s early 70s, but I'm reminiscing now you will have to forgive an old man harping back to the days when men were men and there wasn't any 5wws :nopity::joker:

7029 dave · May 27, 2014

Pete999 said:
Used to run cables in the cavity on all new builds to get away from chasing in, back in the good old days late 60s early 70s, but I'm reminiscing now you will have to forgive an old man harping back to the days when men were men and there wasn't any 5wws :nopity::joker:

Yes Pete, pulled a lot out and made on with new t&e cable on a lot of rewires, and I would still!!, sorry madam got to tear your house part because regs wont allow it, nonsense. Sometimes you have to bow with the breeze . lol

Pete999 · May 27, 2014

7029 dave said:
Yes Pete, pulled a lot out and made on with new t&e cable on a lot of rewires, and I would still!!, sorry madam got to tear your house part because regs wont allow it, nonsense. Sometimes you have to bow with the breeze . lol

"those were the days" Mary Hopkin

7029 dave · May 27, 2014

Those were the days my friend, la la laa la.

telectrix · May 27, 2014

aye. £20/week was a good wage. petrol 5 bob a gallon ( yes, gallon, not silly french litre ), them's deffo were the days.

Pete999 · May 27, 2014

Id wished they'd never ended really

DPG · May 27, 2014

telectrix said:
cavity is already bridged by wall ties and whatever crap the builder has chucked in.

Cavity ties have a drip loop meaning any moisture wicked in from the outer skin is dripped down and not carried through to the inside. Unsupported cables can bridge the inner and outer and transfer water between the skins.
And there shouldn't be any crap in the cavity, but obviously we don't live in an ideal world with caring builders! Daz