Loft insulation and cabling

[stewpot44]

I am about ready to lay some extra (170mm) insulation in the loft of my bungalow. The guidance from npower/buildercentre simply says "where practical, fix cables where they won't be covered". I can lift the shower cabling and the cooker cabling is run around the edges, but, without re-wiring the rest would be impossible. What risks does the rest of the power and lighting cable pose if it is covered, bearing in mind what npower say? Does cabling really get so hot as to pose a fire risk?
Thank you

 

[Click4]

I am about ready to lay some extra (170mm) insulation in the loft of my bungalow. The guidance from npower/buildercentre simply says "where practical, fix cables where they won't be covered". I can lift the shower cabling and the cooker cabling is run around the edges, but, without re-wiring the rest would be impossible. What risks does the rest of the power and lighting cable pose if it is covered, bearing in mind what npower say? Does cabling really get so hot as to pose a fire risk?
Thank you

Hi, Cable does get warm, especially things like shower cables.. certainly ive got a 10mm cable for our shower here and sometimes you can feel the cable after using the shower and it is noticeably warm.

Electric hob cables are probably the same.

The general socket and lighting circuit cables though do get warm but not so much to a noticaeble extent.

not so much it poses a fire risk if the cables are suitibly sized, but covering the cables with insulation does reduce their load carrying capacity as resistance increases with heat.

So never really good to cover cables up with insulation as it de-rates the circuit.

Although it seems a lot of these so called "registered insulation installers" who boast being qualified to do their job dont give a toss about covering over electrical cables... Had a look in the loft of somebodys house recently who had just had loft insulation installed and the morons had covered over all the electrical cables with 175mm of loft insulation instead of sliding it underneath the cables where possible.

 

[PrenticeBoyofDerry]

It’s normally the power circuits that will be effected by thermal insulation, in a standard domestic property.
This would be socket, shower and cooker circuits. They may need to be lifted above the insulation or redesigned, splitting a 32A Ring Final Circuits and making them in to two 20A Radials then run in conduit is a possible way to get around it, without having to upgrade the cable size(CSA)
But depends what current the circuit needs and the size(CSA) of the cables the breaker/fuses are protecting.
Lighting circuits that are in 1.00mm T&E cable and protected by either 5A fuse or 6A MCB/RCBO are usually fine to be covered as the maximum current carrying capacity of the cable even with maximum de-rating is sufficient.

 

[stewpot44]

Many thanks for your comments. Am I right in thinking then that there isn't a fire risk but that the circuit is "de-rated"? Can you tell me what this means and what effect it has?

 

[studentspark]

http://www.tlc-direct.co.uk/Book/4.3.9.htm

That gives some good info on cable rating calculations.

Do the maths and see if you need to move the cables.

Another possibility is to extend the ring. Add some sockets/junctions to the loft and run new cables between which can be clipped out of the way