On 04/10/2020 23:00, Tricky Dicky wrote:

I am in the process of insulating under our kitchen floor, the plan
being to fit the Celotex between the joists and fill any gaps around
the edge with PU foam. However, some of these gaps also have cables
passing through so just to check does PU foam react like polystyrene
with PVC?

No, it does not leach the plasticiser in the way EPS does.

Secondly, does passing through 100mm of insulation have any
significant effect on the cable ratings?

Yes, you would need to de-rate the cable by a factor of 0.78 [1]

So take the column C "clipped direct" rating for the cable :

http://wiki.diyfaq.org.uk/index.php/Cables#Cable_Sizes

and multiple by the de-rating factor as well as any others that apply
(see the article below for full details)

So for example a 2.5mm^2 T&E with a clipped direct rating of 27A would
be reduced to 27 x 0.78 = 21.06A (which is only just high enough for use
in a 32A ring circuit)



[1]
http://wiki.diyfaq.org.uk/index.php/..._in_insulation


--
Cheers,

John.

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