Insulation

[davidl]

Good morning all,

Does anyone happen to know the likely ambient temperature in a loft space in southern england with insulation between the ceiling joists and concrete tiles on the roof, I use the max in the table to be on the safe side but would like to know what it is really likely to be.

Also with regard to insulation, in the case of a 8.5KW shower it is only where the cable goes through insulation twice( up and down) that pushes the cable in this case from 6mm to 10mm. Is it possible to duct the cable at these points to keep it out of the insulation and give it air space?

Thanks to everyone here, this forum is a mine of help and information, got through my NICEIC assessment a couple of weeks ago, it's helpful to know that the answers to most questions can be found here.

Kind regards

David

 

[lilman]

You could use a thermometer if you really wanted to know the air temperature in a loft space - I've got one built into my clampmeter. Also don't let the shower cable touch the insulation and the correction factors are far less extreme.

Cheers

 

[Evans Electric]

This cropped up years ago as I remember . The recomendation was to avoid the lagging if possible then where the cable passes through the lagging , a short piece of 3" downpipe is stood on the ceiling to keep the lagging off the cable (NICEIC) .

 

[green-hornet]

There are differing methods of reducing the effects of high temperatures on cables.

An experiment was carried out years ago on pvc twin and earth clipped direct in loft spaces.Most modern homes now will be insulated to the maximum, however there is lengths of cable that are out of insulation and the calculations show that if at least 1 meter of cable exposed or out of the insulation to the final power using fixture there is enough cooling allowed to make no difference to the suitability of the cable or its maximum amp carrying capabilities.

However having said that we still have to apply all derating as per the regulations.

I have used black gutter pipe as a run over a greater distances of insulation, its fast (no clipping of cables) its easy, and all the cables are above and away from the insulation.

 

[davidl]

Good morning, thanks for the replies, seems like drainpipe is the way to go.

I realise the best option is to avoid the loft but for lighting and in this case the shower it's the only reasonable way to get the cable in, and aside from the derating factor of insulation I understand that theoretically it shortens the cables life. Also if the insulation is polystyrene contact should be completely avoided.

Thanks again, must go and buy a shower!

David