I'd like to shroud the mains cables (about a dozen mixed 2.5mm and
1.0mm) passing through a cavity wall prior to the installation of
blown/pumped cavity insulation. I sense this may be an awkward task
in itself , but want to simplify the upcoming rewire by having a
clearer path for the cables, and not have to worry so much about
derating them all.

The stuff that will be used is apparently some kind of silicone/silica
coated fibre that will 'pack'. Would it be better to let them do the
job and then just pull it out from that section that the cables pass
through?

Plan A is to demount the cables from the CU, push a suitable size of
conduit over 3-4 cables at a time, and feed this through the first
leaf, then the cavity (about 300mm vertical offset :-() and then the
hole in the other brick leaf. May then pop a bit of expanding foam
around the outsides to finalise filling and secure all in place. And
finally reconnect the cables to the CU.

But I can't find a supplier of small amounts (say 5m) of suitably
sized flexible conduit (I have 35-40mm in mind).

Can anyone propose an off-the-shelf supplier, or a different plan?

TIA
IanC

Can you not run the cables up the wall in trunking?

As in 25x16mm & 40x16mm trunking extending across the full width of
the consumer unit to the upstairs floorboard area. Feed cables up
through that - use 1 trunking per cable if 6.0mm or 4.0mm, or combine
a 1.5mm which if loaded to 30% of grouped rating can be disregarded re
grouping factors. Plaster skim, done, wallpaper/paint.

If you must go down the flexible conduit in external cavity route, you
can find 32mm flexible conduit on Ebay quite often. You would need to
use 2-3-4 pieces to get sufficient space to draw in a few cables.
Failing that there is RS and perhaps an electrical factor although
round here they would have a fit if you told them what it was for :-)


I assume your cables are PVC (BS6004 70oC) and not say LSOH (BS7211
90oC) because the sheath on LSOH does not like being drawn across
another cable - it abrades like a hard cheese. PVC is more tolerant of
such handling, LSOH (eg, white sheath since about 2005) is not.

On 6 Nov, 15:55, "js.b1" wrote:
Can you not run the cables up the wall in trunking?

As in 25x16mm & 40x16mm trunking extending across the full width of
the consumer unit to the upstairs floorboard area.

The CU is in the garage, the roof of which is below the 1st floor
level, hence the stagger of the holes across the cavity.

There are two phases to this:

1) Insulation will be installed. I could just leave everything as it
is for now, as long as the cable outer is OK with the insulation
material and I ignore the possible thermal derating issue (the only
moderately heavily loaded cables are the 2.5mm supply to immersion and
kitchen for dishwasher).

2) Install new wiring and CU: At this point I can try a bit harder to
find a new route, although this is tricky due to positioning of soil
pipes on the same wall, solid floor and finish surfaces on opposite
side of wall. Only 'obvious' improvement is to go through the garage
roof, and straight back in through the wall at 1st floor cavity
level. I'm starting to suspect I'll try the 'pull insulation out of
wall' approach...

On Nov 6, 4:19*pm, wrote:
The CU is in the garage, the roof of which is below the 1st floor
level, hence the stagger of the holes across the cavity.

Heh-heh, I know this problem.

What is on the other side of the wall?
- Go straight through the wall through an off-the-shelf oblong brick-
sized ventilation duct. You would need to add an intumescent "letter-
box" pillow, quite expensive but for garage-to-house regs will
probably require it anyway.
- Then go up the wall by nail-clip/screw-p-clip to the wall
- Cover with a 2mm stainless or 3mm galvanised steel sheet re
526-06-06 - earth with 4mm 6491X back to the CU

The earth strictly needs to be accessible, this can be achieved by
cutting the steel sheet so as to leave a protruding tab which enters
an architrave box or socket. You need to file the edge of the box to
the thickness of the sheet plus a little so it just enters. Drill the
tab for M4 and bolt a 4mm ring crimp to it, earth accordingly, done.
BS7671 correct, inspectable, maintainable :-)

Cut 20mm conduit to make spaces for the steel sheet, screw into place,
cover in glass-fibre mesh tape, plaster over. It will ring like a bell
if someone whacks it, so pretty obvious what it is.

If you lack a crimp, for a one-off-job just cut the yellow plastic off
a ring crimp and solder with a soldering iron or blowtorch carefully
(180-230oC). It's a mechanical job and once done you have a service
panel for the future - stainless will never corrode, if you use
galvanised it is cheaper but requires edge-treatment or will bleed
rust through plaster. Check Ebay for sheet metal prices, many will cut
to size, as will some local fabricators - just depends where you are.

Forget going up the cavity, it is a non-starter.
I would not replace the CU (unless damaged, you can replace any
enclosure).
I would not replace the cables (unless damaged, you can replace a
circuit).

On 6 Nov, 16:28, wrote:
On 6 Nov, *
* * wrote:

But I can't find a supplier of small amounts (say 5m) of suitably
sized flexible conduit (I have 35-40mm in mind).

I think you'll find it almost impossible to get 35mm flexible conduit up a
foot *through an average width cavity unless you remove several bricks on
each side. Unless the cables are well overrated the grouping factor will be
likely to derate the cables to below protection level.

--
* B Thumbs
* Change lycos to yahoo to reply

In that case I suspect I'll just let the insulation installation crew
do what they think is right. They seem to believe that there is no
problem, and that my proposals are OTT.

I'll endeavour to address any issues during the rewire.

IanC