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Junction boxes, cables and 250mm Rockwool
In article ,
(Lobster) writes:
The Rockwool instructions helpfully tell you to avoid covering
electrical fittings, junction boxes etc - but how the hell are you
supposed to do that? I've been attaching my cables and any jct boxes
to joists, but these have now vanished. I have visions of attaching
little timber masts to the joists, to attach the jct boxes etc just so
I can see them above the Rockwool! This can't be an unusual
problem...
When running cable inside thermal insulation, you have to derate it
by 50%. The free air rating of 1.0mm˛ is around 14A. In lighting
circuits, it's normally protected at 5A or 6A (and the design loading
maybe even less). This means it's already derated by more than 50%,
so you can cover it safely. Another issue is damaging a covered
cable by stepping on it and not noticing, or something similar.
If you have any other circuits up there, you will have do do a similar
calculation, and you might have to reroute the cable or increase the
conductor size. (Electric shower would be a particular concern,
and ring circuit would need sorting too.)
--
Andrew Gabriel
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