From my electrical fuse box on the ground floor, some cables run
upward inside the cavity wall to the first floor. I am planning to
have the cavities injected with insulation foam soon, and want to keep
the foam away from the cables, to avoid overheating of the cables.

I am thinking I could remove the cables from the wall, then feed some
kind of flexible 3" bore conduit up the cavity and then rout the
cables inside that.

Alternatively, I could re-route the cables up the inside of the house
(in a corner of the hall, for example). Is rectangular-section plastic
trunking suitable for this purpose? There are two 6mm cables, two
2.5mm cables and one 1mm cable.

What are my options, and their merits?

Thank you,

Jeff D

Jeff D wrote:
From my electrical fuse box on the ground floor, some cables run
upward inside the cavity wall to the first floor. I am planning to
have the cavities injected with insulation foam soon, and want to keep
the foam away from the cables, to avoid overheating of the cables.

AIUI you aren't supposed to route cables inside cavity walls; apart from
the possible overheating thing, isn't there the potential issue of the
foam attacking the PVC cable sheath?

I am thinking I could remove the cables from the wall, then feed some
kind of flexible 3" bore conduit up the cavity and then rout the
cables inside that.

Don't know how you'd get the conduit into the cavity, up the cavity, and
then out of the cavity at the other end?

Alternatively, I could re-route the cables up the inside of the house
(in a corner of the hall, for example). Is rectangular-section plastic
trunking suitable for this purpose? There are two 6mm cables, two
2.5mm cables and one 1mm cable.

Either that or chase out the walls and bury the cables

David

On Sat, 28 Apr 2007 13:17:59 GMT, Lobster
wrote:

Jeff D wrote:
From my electrical fuse box on the ground floor, some cables run
upward inside the cavity wall to the first floor. I am planning to
have the cavities injected with insulation foam soon, and want to keep
the foam away from the cables, to avoid overheating of the cables.

AIUI you aren't supposed to route cables inside cavity walls; apart from
the possible overheating thing, isn't there the potential issue of the
foam attacking the PVC cable sheath?

I am thinking I could remove the cables from the wall, then feed some
kind of flexible 3" bore conduit up the cavity and then rout the
cables inside that.

Don't know how you'd get the conduit into the cavity, up the cavity, and
then out of the cavity at the other end?

I was envisaging dangling a line down the cavity, and hauling the
imagined flexible pipe up through. Should be easy enough. But if one
isn't supposed to route cables through the cavity I'd better go for
the internal routing option.

Alternatively, I could re-route the cables up the inside of the house
(in a corner of the hall, for example). Is rectangular-section plastic
trunking suitable for this purpose? There are two 6mm cables, two
2.5mm cables and one 1mm cable.

Either that or chase out the walls and bury the cables

If I opt for the latter, do the cables have to be inside steel conduit
- or is it legal to simply plaster over them?

Thanks,

Jeff

Jeff D wrote:
On Sat, 28 Apr 2007 13:17:59 GMT, Lobster
wrote:

Jeff D wrote:
From my electrical fuse box on the ground floor, some cables run
upward inside the cavity wall to the first floor. I am planning to
have the cavities injected with insulation foam soon, and want to keep
the foam away from the cables, to avoid overheating of the cables.
AIUI you aren't supposed to route cables inside cavity walls; apart from
the possible overheating thing, isn't there the potential issue of the
foam attacking the PVC cable sheath?

I am thinking I could remove the cables from the wall, then feed some
kind of flexible 3" bore conduit up the cavity and then rout the
cables inside that.
Don't know how you'd get the conduit into the cavity, up the cavity, and
then out of the cavity at the other end?

I was envisaging dangling a line down the cavity, and hauling the
imagined flexible pipe up through. Should be easy enough. But if one
isn't supposed to route cables through the cavity I'd better go for
the internal routing option.
Alternatively, I could re-route the cables up the inside of the house
(in a corner of the hall, for example). Is rectangular-section plastic
trunking suitable for this purpose? There are two 6mm cables, two
2.5mm cables and one 1mm cable.
Either that or chase out the walls and bury the cables

If I opt for the latter, do the cables have to be inside steel conduit
- or is it legal to simply plaster over them?

Providing the cable runs are in acceptable locations you can just
plaster over them in shallow chases (most people use plastic capping or
conduit within the chases to protect the cables during plastering and/or
hold them in place.

http://www.niceic.org.uk/downloads/Pocket%20Guide%206.pdf


David

On Sat, 28 Apr 2007 15:08:17 GMT, Lobster
wrote:

Providing the cable runs are in acceptable locations you can just
plaster over them in shallow chases (most people use plastic capping or
conduit within the chases to protect the cables during plastering and/or
hold them in place.

http://www.niceic.org.uk/downloads/Pocket%20Guide%206.pdf

Thank you very much for the help. I'm wondering if I should remove the
cables from the cavity and channel them down an inside wall now. What
is the official objection to running cables up a cavity? I would have
thought that would be the safest place one could have them. Mine have
been that way for about 15-20 years. But if I'm going to be ordered to
have them chased into an inside wall at some stage in the future, I'd
rather do it now, rather than after I have laid laminate flooring
upstairs when they will be harder to access.

Jeff

Jeff D wrote:
On Sat, 28 Apr 2007 15:08:17 GMT, Lobster
wrote:

Providing the cable runs are in acceptable locations you can just
plaster over them in shallow chases (most people use plastic capping or
conduit within the chases to protect the cables during plastering and/or
hold them in place.

http://www.niceic.org.uk/downloads/Pocket%20Guide%206.pdf

Thank you very much for the help. I'm wondering if I should remove the
cables from the cavity and channel them down an inside wall now. What
is the official objection to running cables up a cavity?

Well the objections are as pointed out earlier, but personally I don't
know whether it's a 'best practice' issue or whether it's a complete
no-no given that it's already been installed this way... I expect one
of the several pro electricians who frequent this newsgroup will be
along soon to set you right!

The issue has certainly been raised in this newsgroup several times
before in the past so it would definitely be worth a google.

David

AIUI you aren't supposed to route cables inside cavity walls; apart from
the possible overheating thing, isn't there the potential issue of the
foam attacking the PVC cable sheath?


Does this apply to ALL cables or just power? I have dropped a number
of TV/Sat cables and ethernet CAT5 cables down the cavilty of my
house. We dont have cavilty insulation but I have been thinking about
it. From what I have read/heard, modern insulation doesnt attack the
cable sheath.

Alan

"Jeff D" Jeff wrote in message
...

From my electrical fuse box on the ground floor, some cables run
upward inside the cavity wall to the first floor. I am planning to
have the cavities injected with insulation foam soon, and want to keep
the foam away from the cables, to avoid overheating of the cables.

I am thinking I could remove the cables from the wall, then feed some
kind of flexible 3" bore conduit up the cavity and then rout the
cables inside that.

Alternatively, I could re-route the cables up the inside of the house
(in a corner of the hall, for example). Is rectangular-section plastic
trunking suitable for this purpose? There are two 6mm cables, two
2.5mm cables and one 1mm cable.

What are my options, and their merits?

Thank you,

Jeff D

Why use foam? There is an alternative that most cavity wall firms use like
strands of cotton wool. very effective, doesn't attack PVC or wall ties -
or emerge from any cracks or holes.
I would love to see you try the conduit idea!
Cables will not overheat providing they are the correct size for the load
after they are derated by a factor relating to the type of insulation.

On Sat, 28 Apr 2007 14:06:25 +0100 someone who may be Jeff D Jeff
wrote this:-

From my electrical fuse box on the ground floor, some cables run
upward inside the cavity wall to the first floor.

They shouldn't do. Leaving aside external cabling, they should
either be on the surface or buried in the wall. Who installed these
cables?

I am planning to
have the cavities injected with insulation foam soon,

It is unlikely you will find many people to do it, due to the
problems foam insulation causes. However, you will find plenty of
people who will blow what looks a bit like chopped up fibreglass
into the cavity.

I am thinking I could remove the cables from the wall, then feed some
kind of flexible 3" bore conduit up the cavity and then rout the
cables inside that.

Good luck trying. Anyway, the heat will probably still have nowhere
to go as the conduit will be surrounded by insulation.

Alternatively, I could re-route the cables up the inside of the house
(in a corner of the hall, for example). Is rectangular-section plastic
trunking suitable for this purpose?

Yes it can be used for this purpose. provided the cables are
adequately supported inside it. Alternatively they can be clipped to
the wall and then perhaps covered over. Check the size of the cables
is adequate in the group.

Remember Mr Prescott if you are in England or Wales.


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

On Sat, 28 Apr 2007 15:34:51 +0100, David Hansen
wrote:

Yes it can be used for this purpose. provided the cables are
adequately supported inside it. Alternatively they can be clipped to
the wall and then perhaps covered over. Check the size of the cables
is adequate in the group.

The cables are the right size in normal circumstances. What do they
use to clip the cables to the wall (when inside trunking or in a
chasing)? Is there any trunking available with some kind of easy
clipping system built-in? Anyone provide a link?

Thanks,

Jeff

Jeff D wrote:
On Sat, 28 Apr 2007 15:34:51 +0100, David Hansen
wrote:

Yes it can be used for this purpose. provided the cables are
adequately supported inside it. Alternatively they can be clipped to
the wall and then perhaps covered over. Check the size of the cables
is adequate in the group.

The cables are the right size in normal circumstances. What do they
use to clip the cables to the wall (when inside trunking or in a
chasing)? Is there any trunking available with some kind of easy
clipping system built-in? Anyone provide a link?

Have a look at:
http://www.tlc-direct.co.uk/Main_Index/Conduit_Pvc_Index/index.html
The oval stuff is what's normally used when you chase out a wall; the
capping is normally for new builds (easier because you don't need to
thread the cables though, but is much wider than the equivalent oval
conduit, so you'd need to chase a much wider channel. The capping will
normally wedge itself in place within an appropriately-sized chased
channel without need for fixing; use masonry nails or similar to fix
capping.

For surface mounted trunking (yuck) look at:
http://www.tlc-direct.co.uk/Main_Index/Trunking_Pvc_Index/index.html
The 'backs' of these fix to the wall however you want (self adhesive
pads, screws or whatever; put your cables in and then the 'front' snaps on.

David