There will be different current ratings depending on the installation method and if you have containment or not.

For example a standard 2.5m2 flat twin and earth cable may carry 27A continuous when "clipped direct" - if you install it in conduit in an insulated wall then it can carry 20A - if you put it into a stud wall with insulation both sids of the cable it may carry 13.5A

Essentially all that's happening is the cable shouldn't exceed 70C in normal operation - adding insulation around it diminishes the ability of the cable to lose heat and thus it's derated to compensate

If it is in conduit in an insulated wall then the figure of 20A is important - it's the point of minimum compliance for a cable arranged in a typical UK ring final circuit prottected by a 30/32A MCB.

So you can bury it to your hearts content in insulation - but you might want to consider the effects of EPS on the polymers in uPVC conduit and in the cable - generally thay aren't a good mix long term. If using EPS, I'd go for a 50mm deep service void

regards

Barney

Would polypropylene conduit be cheaper than metal and compatible with EPS?

Metal conduit will need a bit of skill and attention - particularly if you want a complete tube install rather than just the wall drops

Polypropylene is less affected by EPS - but it's more expensive - if you go for it, look for something like adaptaflex PP range.

I wouldn't worry about the smoke and fume - if you have fire in the structure that's affecting the adaptaflex then the EPS is toast anyway

Well I guess it depends on who you believe - if FRS can't find an obvious cause then it goes down as electrical so the figures get skewed. I think IFE still publish monthly fire stats in the journal - by cause, cost, sector and loss of life if memory serves

That said, the RCD(s) should deal with a lot of issues before they really start (the yanks still often call them arc fault interrupters rather than ground fault )and we put most of our connections in metal boxes anyway. Much existing stock isn't blessed with an RCD though

In my experience of it, it's bloody downlight transformers that are a big contributor - particularly the cheap and nasty ones with a "China export" mark on them - coupled with dimmers and stuffed into dusty voids along side blisteringly hot GU10's then it's a wonder we don't have more fires than we do - still, I like to think of it as darwinian selection - if you have so little taste as to want downlights everywhere then fire is the inevitable consequence.

Regards

Barney

Yes, my bad - you would need both for complete protection - the RCD will give you almost as much protection as the AFCI though - unless you are also using "combination" types, that are then prone to nuisance tripping in typical UK circuit configurations - particularly as the originate from protecting aluminium conductor circuit wiring I believe - something there is very little of in the UK

regards

Barney

Presumably that's appliance flexes and the like though - rather than the fixed wiring being damaged - although I guess protection at source covers both the circuit and the flex.

Typical UK domstic witing now would have RCD/GFCI's on all wet areas containing a bath or shower, all socket circuits and all unprotected cables less than 50mm deep - so given we don't wire "room" circuits that's the whole house !!

Regards

Barney

Posted By: barneyPresumably that's appliance flexes and the like though - rather than the fixed wiring being damaged - although I guess protection at source covers both the circuit and the flex.

Yes, things like lamps and alarm clocks, for example. Where there's enough insulation damage to cause an arc, but not enough current flow to trip the breaker.

We tend to go overboard on circuit breakers - my kitchen alone has at least 11!!

Paul in Montreal.