Internal wall insulation and cables

[Tony]

I'm currently renovating an old cottage, as I'm having to put up some stud work I'm thinking of installing some insulation (100mm) before I plasterboard it.

This will mean that I'll end up with about15 meters of the ring main cable (2.5mm T&E on a 32 amp fuse) sandwiched between the outside wall (which is 2' solid stone) and the insulation (not in the insulation itself). Do I need to worry about de-rating the cable in this situation?

The electrics are in good condition and were tested about two years ago.

Thanks for any advice.

Tony

[John Rumm]

This sounds like reference method 102. See:

no, the current carrying capacity still meeds the requirements for a normal ring circuit.

(in reality a stone wall will perform better than a plasterboard - so you have more latitude than the raw numbers suggest)

[ARWadsworth]

There is an important point on installation method 102 that the cable should be on the internal side of the insulation.

This is because the cable will have to pass through the installation to reach an accessory on the internal wall.

However with reference to table 52.2 in

believe that the 100mm of insulation should not be a problem as the cable derating factor is 0.78.

[Tony]

le

Thanks to both of you - looks like I'm OK.

Tony

[John Rumm]

I believe that the 100mm of insulation should not be a problem as the cable

By the time you take the depth of the back box out of that, and a bit of air space behind it - it ought to have even less effect - especially if you use a metal box mounted on a block of wood screwed to the masonry rather than a dry lining box.