Lighting Electrics and Insulation

[Bloosman]

Hi guys,

I appreciate this has probably been asked countless times, and I have read similar threads on here, but still can't get my head around it...

I am redoing the ceiling in our flat roofed lounge extension, after installing a Velux flat roof light.

I now intend replacing the original single electric roof light with a couple of ceiling mounted spots (not downlights cut into the ceiling) and wonder how to run the wiring to them.

Previously there was NO insulation between the plasterboard and flat roof deck, so I'm looking at putting in some Kingspan or similar.

Should I run the cabling above the insulation (in the air gap) and then through cut outs to the lights, or will I be ok to have it between the insulation and the ceiling material...???

It's all pvc cable, fitted to circuit breakers at the fuse box end....

Ta,

Dougie.

 

[ericmark]

This may seem strange but you need to go back to basics rather then try to follow all the rules. And the basic thing is heat must be able to leave the cables. This could be by air passing the cables or it could be by having the cables against a heat conducting surface. This surface could well be the wooden beams or the plaster board.

Untitled

• ericmark
• 3 Oct 2011
• 1

This picture shows installation method 101 and you can see how it shows the cables against the beams or plaster board. With that method 1mm cable is rated at 10.5A and since most ceiling roses are rated 5/6A normally in most houses the MCB feeding the lights is limited to 6A as a result so there should be no problem with lighting.
Only with power cables is one likely to draw enough amps to cause problems.

 

[ban-all-sheds]

Plus if you take the cables through the insulation you'll have to derate them anyway, and by puncturing the vapour barrier you risk condensation and rot in the roof.

 

[Bloosman]

Thanks folks,

Food for thought...I'll maybe go with the fixing to the plasterboard after the Kingspan is inserted.

Dougie.