Attic insulation top up & Electrical wiring

[fdiddy]

Hi all, I currently have 100mm attic insulation and would like to top it to 300mm in total. Problem is electrical cables are running on the existing insulation with very little slack.can the insulation be laid over the wiring without a fire risk. Thanks

 

[hllns]

More of an electrical question really.

Cables enclosed in insulation have a lower current carrying capacity, something that matters a great deal for a cable feeding something like an electric shower but a lighting circuit might be OK, are the cables clipped to joists or just sitting on top of the insulation and do you know what they're feeding?

 

[fdiddy]

Mostly lights,electric shower 1 upstairs and downstairs. Typical housing needs...

Most laying on the insulation with some on rafters

 

[JohnD]

Lift the old insulation and lie the cables directly on the plaster ceilings. You can put insulation over it if it is uninsulated on one side.

 

[fdiddy]

is that commonly done and does it pose any risk?

 

[JohnD]

Yes and no

But take extra care with the shower cables as they carry a heavy load and will get warm. Perhaps put something rigid on them to ensure the insulation does not engulf them. If you have any downlighters coming through the ceiling you can buy hoods for them, or if you have plasterboard handy, make open-bottomed boxes to cover.

Lighting cables carry very small currents so not a worry.

 

[fdiddy]

ok perfect -thanks for the advice.
Making an assumption here but wouldn't the breaker kick in if there is too much load and subsequent heat going across, in say that example of a shower?I already have the hoods for the downlighters so good on that front

 

[JohnD]

No. As far as the breaker is concerned, it is just a resistance heating load.

It does not increase current draw as the loads are in series. The electric shower will get a bit cooler but you may not notice.

 

[EFLImpudence]

I do think the showers details ought to be investigated before covering the cable with 300mm. of thermal insulation.
Laid on the top as at present being the equivalent of Method C.