Using a cavity wall gap for cables

[Pat H]

Looking at a job that needs cables running up to a loft space.
Had originally planned a cable route from CCU through wall into garage (part of side extension)
along top of garage inside wall then up through the bedroom above into the loft space.
All surface mount clipped direct.
A good few cables to run: Replacement show feed, New Ring main new lighting circuit.

But looked today and I have a much more direct route via the original gable end wall cavity space.
It's no longer an external wall as the side extension sits the other side of it.

I have the CCU under the stairs with most of the houses cabling already going into that cavity.
About 2 metres above it I have a doorway (from 1st floor landing into side extension) so I can access the cavity space there. 2 metres above that I have access to the top of the cavity wall.
So I have line of sight of the whole cavity run. Can see no issues with sharp edges or debris. Nothing will fall from the top down the cavity. I can support the cables in 3 places along the vertical run.

What do people think? I could go safe and use SWA and that was my first thought but it looks ok to me and saves me over 6 metres of cable runs.

 

[DPG]

Contentious issue this one I personally don't like it for various reasons:

1. Support of cables is usually difficult and normally not done.
2. Cavity is bridged in various places with no possible drip point in the middle. Probably won't cause an issue, but not ideal.
3. Not in a prescribed zone, so what happens when someone legitimitly drills through to the other side for an outside light, aerial cable, CCTV camera cable, etc and hits your hidden cable.

Good one for a debate though!
Daz

 

[Pat H]

I can support the cable at 3 accessible points on it run up. Drip point not an issue as this is an internal wall now not external.
The wall each side of the cavity is more than 50mm thick so the cables are deep compared to the surface.
unlikely to be any holes bored through as this is an internal wall now not external. And if they do they will hit the current hosue cabling that currently lives in that very cavity.

 

[DPG]

Yep I can see your circumstances are different and my points may not apply to your scenario. Just stuff to bear in mind generally with cavities.

Daz

 

[Pat H]

Yes thanks. As you said it maybe an interesting debate

 

[Pete999]

Used to be done as a norm many moons ago, but rules change, Regs change.

 

[Deleted member 26818]

Regs still allow a building void to be used as containment.

 

[Pat H]

My biggest concern would be the spacing between supports vertically. But I can probably solve that as well. If I allow enough cable slack initially I can affix the cables to a support and lower that into the cavity and then secure. Other than that I can't think of any other reg restrictions. Every circuit will be on an RCBO so has additional protection.

 

[7029 dave]

IMO, up you go.

 

[Deleted member 26818]

Additional protection = additional nuisance.

 

[Wilko]

WRT cable support - have a look at OSG Appendix D. Reading this and from what I understand of your situation, item (g) seems to say up to 5m vertical will satisfy Reg 522.8 (with a couple of conditions).

 

[Pete999]

Common sense should prevail on this occasion.

 

[DPG]

Common sense should prevail on this occasion.

Agreed.

 

[1Justin]

If it's now an internal wall, I can't really see what would be the problem. (Not cavity filled with anything, esp polystyrene beads?). Regs call only for "appropriate" support to avoid excess strain, and OSG says OK for 5M provided there is a support radius. That would prevent drilling a hole and shoving them in, but (just say) a conduit elbow bend were pushed through at the top.. I'd go with something like that.

 

[Pat H]

Yes the wall is empty no cavity filling at all. Loads of space at the top so can ensure a nice bend radius. Not so easy at the bottom as it comes into the rear of the CCU. But the bend there has no load on it.