Cables under concrete floor
 

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.

Thanks for any ideas,

Martin

Cables under concrete floor
 

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/
.... 4 food groups: fast, frozen, microwaved, and junk

Cables under concrete floor
 

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.



If PVC cable is unsuitable for this - why is it suitable for direct bury in
roughging when used on blockwork walls ?? it's the same material in
contact ?


Rick

Cables under concrete floor
 

In message ,
"Rick Hughes" wrote:

Martin Angove wrote:


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.



If PVC cable is unsuitable for this - why is it suitable for direct bury in
roughging when used on blockwork walls ?? it's the same material in
contact ?


Hmmm... come to think of it, what the OSG probably means is not to lay
cable and then pour concrete all over it. It is possible that something
in the unset/setting mix will react with the PVC. I really don't know,
and someone else here can probably advise better. When putting cable in
channel, the stuff is already set and so presumably more-or-less inert?
They're not worried about wet plaster - good job too!

Hwyl!

M.

--
Martin Angove: http://www.tridwr.demon.co.uk/
Don't fight technology, live with it: http://www.livtech.co.uk/
.... Dammit Bones, I'm a captain, not a doctor!

Cables under concrete floor
 

"Martin Angove" wrote in message
...

Hmmm... come to think of it, what the OSG probably means is not to
lay cable and then pour concrete all over it. It is possible that
something in the unset/setting mix will react with the PVC. I really
don't know, and someone else here can probably advise better. When
putting cable in channel, the stuff is already set and so presumably
more-or-less inert?

I suspect it's more physical than chemical. Concrete (as opposed to sand &
cement screeds or plaster undercoats) contains stone chippings with sharp
edges. You wouldn't want to put a relatively fragile cable through mass
concrete which is going to be poured by the barrow load (or more) then
tamped or settled with a vibrating poker. The (un)delicacy of the
concreting operations just isn't compatible with the cable - even 10 mm^2
T&E starts to seem small and fragile in those circumstances...

In the floor screed I'd still use PVC conduit though - it's cheap and saves
an awful lot of hassle if you need to replace the cable.

--
Andy

Cables under concrete floor
 

Interesting. THE Boat Safety Scheme (Inland waterways) does not permit
PVC cable layed in polystyrene insulation foam as conatact makes the
PVC brittle and a fire hazard.

On Mon, 13 Oct 2003 00:19:24 +0100, "Andy Wade"
wrote:

"Martin Angove" wrote in message
...

Hmmm... come to think of it, what the OSG probably means is not to
lay cable and then pour concrete all over it. It is possible that
something in the unset/setting mix will react with the PVC. I really
don't know, and someone else here can probably advise better. When
putting cable in channel, the stuff is already set and so presumably
more-or-less inert?

I suspect it's more physical than chemical. Concrete (as opposed to sand &
cement screeds or plaster undercoats) contains stone chippings with sharp
edges. You wouldn't want to put a relatively fragile cable through mass
concrete which is going to be poured by the barrow load (or more) then
tamped or settled with a vibrating poker. The (un)delicacy of the
concreting operations just isn't compatible with the cable - even 10 mm^2
T&E starts to seem small and fragile in those circumstances...

In the floor screed I'd still use PVC conduit though - it's cheap and saves
an awful lot of hassle if you need to replace the cable.

Lawrence

usenet at lklyne dt co dt uk