Running Cables Through Insulation

Mr Gumby

Are there guidelines on running domestic wiring through insulation?
I'm not refering to physical contact with polystyrene etc reacting with cable insulation but rather the downgrading of current carrying capacity and possible overheating.
I'm concerned with the additional layers of insulation in attics and the running of cables in insulated stud work. Particularly because of the many new wall sections for timber frame due to our interest in better insulated homes.

M cebee

ya-the ccc should be de-rated accordingly

it'll be in the back of rules

Bruthal

Cables hardly warm up at all once they have the proper rated breakers on them, so you would wonder is any de rating really needed.

Mr Gumby

I'm thinking in particular about say cables to storage heaters etc, where the cable size may have to increase even for a normally ok load or radial circuits where it may be necessary to downsize the breaker, run cables in metal conduit or limit the no. of outlets.
I dont have a copy of rules, what is the max ccc of a 2.5 T&E run through insulation compared to run in air please?

M cebee

for sustained heating loads-you're normally concerned with the rating of switchgear
it's mentioned in the rules



don't get caught having to downsize breakers anyhow:)

design current first---then breaker--and lastly cable
http://www.tlc-direct.co.uk/Book/4.3.9.htm

Mr Gumby

Thanks for that link it looks like it has everything I will need.
I see your point completely about cables.
How about though were existing cables get buried with a new layer of insulation?

Are there any areas that the Irish regs differ greatly from the British apart from say 1.5mm lighting rather than 1mm, or is that too complex a question?

M cebee

ya that's a uk link but it's informative

you'd have to check ET101 to be sure


there's a good few differences on rcd'ing final circuits over there

and they do the conversion from TN-C-S to TT for outbuildings -a lot of the time anyhow

a lot would be similar