Rednadnerb
wibbled on Thursday 01 April 2010 13:43

Hi all

I am doing up the kitchen and have internally insulated the three of
the walls
with 50mm thermoboard. I thought it would be a good idea to leave a
gap at the bottom to run pipes and cables around the bottom of the
walls and up to the kitchen units. I need to run gas, hot and cold
pipes and the ring main cable.
The guy doing my heating and electrics is uncomfortable with this and
wants to drop the electricity cables down vertically from the ceiling
thereby cutting a swath through my thermoboard.
Is he being over cautious? Isn't there some way to run them together
using conduit or lagging or even a decent spacing between the cables
and pipes, I can make the width of the channel as wide as necessary.


Any suggestions appreciated.

Gas pipe =35mm dia should be =25mm from electrical cables according to my
OnSite Guide (the reference there is to BS6891:2005 clause 8.16.2). The
distance may be reduced "if a pane of insulating material is interposed" or
the gas pipe "is PVC wrapped".

Cold water and electrics - main issues are access to soldering joints by
plumber (ie is he going to stick a blowtorch on the cable) or mechanical
damage due to wielding spanners/wrenches.

Hot pipes - normally a reasonable gap and/or pipe insulation would be OK in
free air (say under a suspended floor), but burying a pipe and a cable in an
insulated trench which is what I understand you have, is not something I
would contemplate. Reason - you'd really have to assume the ambient air
temperature in that void *may* reach the temperature of the hot pipe at
worst. If that is 70C, your PVC cables are now derated to zero (ie they are
at their maximum temperature). Even at an assumed 50C air temp, you'd be
upsizing your cables. I am assuming that the pipes will be covered? If not,
sections may become implicitly covered by the units???

You really want a separate route for the electrics. You are going to have to
apply derating for enclosing them in insulation anyway. A little more detail
on your proposed "trench" could be helpful.

So, no, I think he is right to question this.

Given there is often a void at the back of the units, how about a surface
run in conduit for good measure, somewhere upwards, where the cable is
behind the units? This is what I have done.

HTH

Tim

--
Tim Watts

Managers, politicians and environmentalists: Nature's carbon buffer.