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https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl DIY Forum >> Electrical Questions >> Internal wall insulation https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl?num=1370877549 Message started by CWatters on Jun 10^th, 2013, 4:19pm

Title: Internal wall insulation
Post by CWatters on Jun 10^th, 2013, 4:19pm

Many houses with solid walls have wiring buried in them.

Is it typically necessary to derate the ring mains when adding internal wall insulation?

Have any experiments been done to show that this is/isn't necessary? I recall some tests were done on lighting circuits under loft insulation but have any been done on walls?

Title: Re: Internal wall insulation
Post by Lectrician on Jun 10^th, 2013, 6:57pm

The regs allow for this in table 4D5.

If the cable is in a stud wall and touching the inner wall surface (dissipates heat), then 2.5mm can carry 21amps, so fine for rings and 20amp radials.

If it is run in the middle of thermal insulation, then the rating is 13.5amps, so not large enough for a ring or a radial. You would need to increase to 4mm. This has a rating of 17.5amps run in the middle of insulation, so fine for a ring, but still not OK for a 20amp radial.

[gallery fullsize]Lectrician/1370887036.png[/gallery]

Title: Re: Internal wall insulation
Post by TIMBA-WOLF on Jun 10^th, 2013, 9:17pm

The extension we built last year in Chislehurst, had so much cavity and wall board insulation (foam backed PB's) and 14" thick ceiling insulation that all cables were uprated to 2.5mm for lighting, and 4mm for the ring main.... :-X

i wont post what the sparkie thought of all the insulation...LOL!

Title: Re: Internal wall insulation
Post by CWatters on Jun 12^th, 2013, 10:25pm

Thanks Lectrician. That suggests any house needing internal wall insulation probably needs a rewire to 4mm or derating of the ring?

I've not heard of people rewiring. As I understand it they normally just raise the sockets up the wall a bit to get enough wire to feed through the insulation.