Loft Insulation and Electric cables

[J5]

How do

This winter we plan to further insulate the house by rolling out some new loft insulation over the existing Rockwool? (the nasty gets everywhere itchy stuff). Is it ok to cover over mains cables that are on top of the existing insulation? There is a 6mm shower cable and i think i can see a junction box up there.

Thanks in advance.

Jas.

 

[dingbat]

Cable surrounded by insulation over a length exceeding 500mm (yes, just half a metre!) are derated from their maximum current-carrying capacity by 50%. This means your 6 sq mm shower cable drops from 47A to just 24A. In other words this cable is in danger of overheating if you insulate it.

Ideally it should not even be in contact with insulation, but then there's real life...

In any case, cable in the loft should be clipped to the side of joists, not run over the top of them and certainly not just laid will-nilly over the insulation. If you have enough cable up there you could consider providing some support to raise it above the insulation for its run through the loft.

 

[Paul Barker]

No it's not OK it prevents them shedding heat, and they are sized using a formula which is altered when surrounded by insulation.

SO what the advice is that the cable be fixed to a batten which allows it to dissipate heat through the wood. The cable which runs along joists and struts should already be clipped to that wood so it is safe.

 

[J5]

LOL, i knew it was a stupid question!

Thats another mission to add to the list then as well drylining our cold cavityless walls

Cheers for the advice.

Jas.