In message ,
(Martin Pentreath) wrote:

I need to do some rewiring in my kitchen. It has a concrete floor, and
the easiest way to route the twin & earth would in places be under the
floor. Once everything is done I'm intending to put Wickes electric
floor heating on top followed by ceramic tiles.

So, what I'd like to do is to put my SDS drill to good use to gun up
some channels in the floor, lay the cables and fill in the channels
with mortar.

Is it OK to do this? Must I use conduit (in which case I'd go for
http://www.screwfix.com/app/sfd/cat/...81966&id=12389 )?
Are there rules about the course the cables must take (no diagonals,
etc)?

While I'm at it I intend to put some cat5 and coaxial cables in as
well (although not to close to the electrics), anyone foresee any
problems with that idea? I'm a bit worried that the underfloor heating
might bugger it up.


Thought someone else would have answered this one by now... don't have
much time, but here goes anyway.

1: PVC cable is unsuitable for embedding directly in concrete according
to the On Site Guide, table 3A (p94) so some sort of conduit is called
for.

2: If you use metal conduit (watch out for its earthing) then depth and
route shouldn't be an issue - the usual rule is 50mm below any surface
is "safe" or if less than 50mm, must be "suitably protected". The only
caveat I'd see to this is that some people have a habit of firing nails
into concrete floors in order to fix partition battens down (etc.) and any
such nail is unlikely to find a bit of, even metal, conduit a problem.
However, if you are laying electric UFH on top then anyone who wants to
do this is probably a bit silly.

3: The UFH will certainly affect the capacity of the cable - at what
temperature does it (the UFH) operate, and how well insulated is it (the
UFH) to below? Again, the OSG has advice in the forms of tables 2A (p93)
and 9B (p159) however, if you can be sure that the ambient temperature
of the cable will not get above 30C you can assume that 2.5mmsq PVC
cables in conduit will be able to carry at least 20A, and are hence
suitable for their "standard" circuit configurations. This information
is in table 6F of the OSG (p126).

HTH.

Hwyl!

M.

--
Martin Angove: http://www.tridwr.demon.co.uk/
Don't fight technology, live with it: http://www.livtech.co.uk/
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