Loft Insulation and Electrical Wiring

[KateMoss]

Hi, Sorry, this is posted on 2 forums - I originally put it under loft insulation but have been advised that I might get a better answer from the 'sparks' so here it is again.
I am about to install loft insulation (mineral wool - SPACE 'Loft Roll') and the instructions on the packing say 'Insulation must not be laid over electric cables'.
This implies I need to lift the lighting cables which are currently (ha ha !) fixed to the joists so that they end up above the finished level of the new insulation. (There is practically no insulation there at the moment but they would be buried by about 200 mm if left as they are).
I asked a pro who came to give an estimate if his company would raise the wiring and he said 'No'.
I'm sure the instructions are good advice but it seems a bit over the top to me; do I run a serious risk by not following them? Thanks.

 

[holmslaw]

..

 

[KateMoss]

As long as you have pvc wiring and lighting circuits fed via 5/6Amp cartridge fuses or mcb's, you will be ok. The only problem you could have is if there are any cables feeding electrical heating loads.

Thanks for that, I'm pretty sure I conform to your specs but I'll check it out.

 

[PrenticeBoyofDerry]

Normally the derating factor involved, doesn't effect lighting circuits that are protected by 5/6Amp devices, as the minium cable CSA used is normally 1.00mm twin and earth, will safely carry the current.
If the lighting circuit has a high load and higher rated protective devide are used it could be an issue. So best check the cable size and fuse/breaker size and type.
Then a more informative answer can be given.

 

[KateMoss]

Thanks PrenticeBoyofDerry, I have a B6 (or NSB06) fuse and wiring that is either 1 or 1.5 mm so I believe I am in the clear. All lights are single bulbs so no unusual loads.

 

[PrenticeBoyofDerry]

Thanks PrenticeBoyofDerry, I have a B6 (or NSB06) fuse and wiring that is either 1 or 1.5 mm so I believe I am in the clear. All lights are single bulbs so no unusual loads.

That sounds okay as 1.0mm even if derated by 50% will carry current safely.

 

[Chri5]

You haven't got an electric shower then ?

And you haven't got any GU10 style flush fitting lights ?

Shower = must keep cable clear of insulation.

Spots = Must have airflow to shift heat

 

[KateMoss]

Thanks Chri5, Actually I do have the spots but was aware of the point you make so didn't mention them. Re. shower - the only wiring in the loft is the lighting.

 

[PrenticeBoyofDerry]

You should keep the insulation at least 150mm from the fitting of the downlight/spots.

 

[KateMoss]

You should keep the insulation at least 150mm from the fitting of the downlight/spots.

Thanks again!!

 

[PrenticeBoyofDerry]

No worries, you should be safe now!

 

[ban-all-sheds]

And you should build a sealed structure over the lights. No point insulating if you're going to leave holes in the insulation -

1) You'll get draughts coming down through the lights when they aren't on.

2) When they are on you'll get convection currents drawing dust upwards which over time will make dirty patches on the ceiling

3) You'll get warm moist air entering the cold loft which will cause condensation and damage to the timbers - this will be particularly acute over bathrooms, and will contravene the Building Regulations.

• http://www.nhbc.co.uk/NHBCPublicati...ical/StandardsExtra/filedownload,16553,en.pdf
  
  
• Pre-formed cap to seal downlights: http://www.aico.co.uk/firecap_loftcap.htm (It's NOT a firehood....)
  
  
• IET article on installing downlighters safely

 

[KateMoss]

Thanks ban-all-sheds, More good advice which I will endeavour to follow.