On 05/10/2020 06:23, RJH wrote:
On 5 Oct 2020 at 02:20:01 BST, "John Rumm"
wrote:

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

Richard


Should also have added, that it does depend a bit on what you mean bu
"in insulation". The worst case is literally that - surrounded on all
sides by insulation. Some cases are less onerous however - say wan its a
cable against a conductive surface like a wall or plasterboard, with an
insulation covering. See the installation methods section he

http://wiki.diyfaq.org.uk/index.php/...lation_Methods

Thanks - I did something similar recently, but 50mm celotex, and routed the
cables through the floor/insulation using some flexible c.3cm quite heavy duty
cable tidy/trunking fixed with foam.

The 'worst case' was 4 cables, and while there could be quite a lot going on
(oven, kettle, toaster etc), my method was reasonably neat and seemed like it
might be effective. But not, I see now, one of the reference methods. I've yet
to finish skirting etc and could easily take out the trunking and clip the
cables to the joist a cm or so apart - might that be better?

Don't worry too much about matching the method, there are a much larger
number of installation methods documented in the full version of BS7671.
Its more the principle to follow.

So cable grouping is one - note that its based on the number of circuits
rather than the number of cables. Also if a cable is expected to carry
less than 30% of its grouped current rating, then you can ignore it from
the count of grouped cables when working out the effects on other cables.

Spacing cable helps. Having them clipped to a thermally conductive
surface helps - even if they are covered in insulation.



--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/