Loft Insulation and Electric Cables


27 Sep 2005
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United Kingdom

I have read the previous forums on this topic, but would still appreciate some clear advice. I am planning to top up loft insulation to 300mm thick overall.

Existing cables in the loft space as follows:-

- Upstairs socket ring main around loft, clipped to joists - part covered in existing insulation (cables drop down to sockets in wall)

- Upstairs lighting cable clipped to joists, part covered in insulation.

When I say part covered, I generally mean the insulation is to one side of the cable, i.e. the other side is clipped to the timbers.

Is it best to unclip all the cables and place loosely on top of the new layer of insulation? or is this just needed for the socket ring main?

House is approx 16yrs old, with cartridge fuses in the CU and RCD on all except lighting circuits.

Look forward to peoples thoughts on this
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I forgot to say the lighting cables are 1.5mm T&E and ring is 2.5mm T&E

The ring is more problematic, is it possible to raise the cable above the insulation and where it passes through insulation sleeve it in some 32mm drainage pipe.

If a cable is running through insulation, albeit with an air gap (eg by using 32mm drainage), how big does that gap have to be before there is no need to derate? A small gap will restrict airflow and therefore will still reduce the CCC of the cable. It seems to me that there should be a gradual reduction in the de-rate factor as the ratio between the overall cable CSA and the CSA of the gap increases from zero to some point where no de-rating is needed.

( I don't know - which is why I'm asking)
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The lighting is protected by a 5A fuse.

With reagrd to the socket ring main, there is sufficient slack to lift this above the new insulation and just lay the cables on top of the insulation.

Is this ok?


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