Routing Cables Through Rafters and Insulation


Postby Rosa21 » Tue Dec 13, 2016 5:07 pm

I need to route lighting and socket cables in a small single story extension with a pitched ceiling. The rafters are 150mm and we'll be putting 100mm of insulation between the rafters. The cables need to run through the rafters. I believe that the holes for the cable are supposed to be drilled centrally in the rafters to avoid weakening the structure, but this would mean that the cables would be surrounded by insulation which apparently is a bad idea.
I can't go through the floor as it's a concrete slab, so the rafters are the only option. Any advice on how to compromise between weakening the rafters or having overheating cables? There will be a 50mm cavity between the insulation and the roof membrane. Can I shift my rafter holes up a bit to allow the cable to sit on top of the insulation? Or is that a bad idea?
Rosa21
Rank: Labourer
Progress to next rank:
0%
Posts: 1
Joined: Tue Dec 13, 2016 4:56 pm

Sponsor

Simply Build It

Postby kbrownie » Tue Dec 13, 2016 10:37 pm

Do you have a 50mm void above the rafters, if so you can avoid holing them for cable routes.

If routing cable through thermal insulation, then the cable must have the correct derating applied for reference method used of installing it.
For most lighting circuits that are protected by a 6A device using 1.00mm2 T&E you should be fine. But any power circuits, it will mean the cable size of the circuit must be increased to safely carry the current demand of the circuit.

http://www.nhbc.co.uk/NHBCPublications/ ... 553,en.pdf
kbrownie
Rank: Project Manager
Posts: 1900
Joined: Mon Mar 05, 2007 9:36 pm

Display posts from previous
Sort by
Order by



  • DIY How to Project Guides

  • DIY how to tutorial projects and guides - Did you know we have a DIY Projects section? Well, if no, then we certainly do! Within this area of our site have literally hundreds of how-to guides and tutorials that cover a huge range of home improvement tasks. Each page also comes with pictures and a video to make completing those jobs even easier!



 


  • Related Topics