Insulating a suspended floor - what to do with cables ?

stevewestern · 28 Jun 2013

I seem to remember reading something about ring main cables and celotex/kingspan not going well together but cannot remember what was said or why...
Can anyone please remind me what the deal is ?

Thanks !

SimonH2 · 28 Jun 2013

Probbaly better asked in teh electrics section, but there are two things that come to mind.

Firstly, if you insulate the cable you lower it's current carrying capacity. That may mean the cable is no longer rated for the protection (fuse or circuit breaker) upstream of it. This never seems to bother the people doing loft insulation.

Secondly, the one I recall is polystyrene where the plasticisers in the PVC react with the polystyrene. Someone posted a photo where a cable had "sunk" through a sheet of polystyrene ! Advice is that a cable exposed in such a way will be scrap as the plasticiser will have been leached out and the PVC will now be hard and brittle.

geraldthehamster · 28 Jun 2013

stevewestern said:
I seem to remember reading something about ring main cables and celotex/kingspan not going well together but cannot remember what was said or why...
Can anyone please remind me what the deal is ?

Thanks !

What exactly is your plan? When I insulated under my suspended ground floor with Celotex, I left a gap of a couple of inches between the top of the Celotex and the underside of the floorboards, and all my mains cable runs in that, i.e. not enclosed in the insulation.

Cheers
Richard

stevewestern · 29 Jun 2013

Thanks for the replies - the plan is to lift the floorboards, insulate between the 100x75mm joists with celotex then lay chipboard with maybe another thin sheet of celotex between the joists and chipboard.
Having lifted more of the floor it now looks like I can run my cables down from the sockets and below the joists in chases so they won't be in contact with the insulation and protected by some capping or conduit which I am assuming will be perfectly acceptable as the cables will run in free air.

geraldthehamster · 29 Jun 2013

stevewestern said:
Thanks for the replies - the plan is to lift the floorboards, insulate between the 100x75mm joists with celotex then lay chipboard with maybe another thin sheet of celotex between the joists and chipboard.
Having lifted more of the floor it now looks like I can run my cables down from the sockets and below the joists in chases so they won't be in contact with the insulation and protected by some capping or conduit which I am assuming will be perfectly acceptable as the cables will run in free air.

Depending on the way things run, could you clip them to the underside of joists, and/or to the wall just below the joists?

Cheers
Richard

stevewestern · 29 Jun 2013

That sounds about right Richard - Having been out of the loop regarding regulations for a long time it all seems so complicated so I want to err on the right side just in case....!

geraldthehamster · 1 Jul 2013

stevewestern said:
That sounds about right Richard - Having been out of the loop regarding regulations for a long time it all seems so complicated so I want to err on the right side just in case....!

I've no idea about the regulations; I'm just concerned with what's safe and what's practical.

Cheers
Richard

stevewestern · 1 Jul 2013

Likewise !!!

securespark · 1 Jul 2013

The regulations tell you what's safe with regard to the wiring.

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Insulating a suspended floor - what to do with cables ?

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