On 2007-09-17 18:42:09 +0100, John Rumm said:
jkn wrote:
This thread has prompted me to read that useful section on the FAQ.
There I see it stated that
"SWA is frequently not brought right into the building at the head end
since it is relatively inflexible and difficult to work with."
What is done instead then, please? I was thinking of an outbuilding
supply using SWA and would be interested to learn about the options.
If you read on a bit to the section on installing the sub main it gives
some of the options:
http://wiki.diyfaq.org.uk/index.php?...g_the_sub_main
The
usual solution is to fix a waterproof box of some description outside
and run the SWA into that with appropriate glands. You can then drill
straight through the wall from the box to allow a cable to continue to
the supply. This can be in T&E which is much simpler to route and work
with than SWA.
Spelsberg A-Boxes are good for this. There are a number of sizes,
plus different sizes of terminal strip inside suitable for terminations
of the range of conductor sizes likely to be used. The terminals can
be located in several positions inside the box to make termination of
the cable conductors easy. There are 20mm and 25mm knockouts on all
sides and at the back. The lid with seal This brand is
available inexpensively from RS and I think Farnell as well as
electrical wholesalers. I've also seen similar products from
manufacturers such as Fibox which are essentially the same thing.
Having said all of that, I have just done an SWA installation where I
didn't want to have an exterior box. This was for power to some
exterior lighting whereby the cable is run under the drive to a fixture
at the end. 2.5^2mm 4 core was used and has an overall diameter of
just under 15mm so fairly chunky. The supply for it is from an
installation in the garage and the cable position is very much on view,
so I didn't really want the box solution. As John suggests, turning
the cable through 90 degrees wouldn't have been a good solution either.
The solution I came up with was to determine a cable entry position one
course of bricks above the DPC - about 250mm above the ground. Knowing
the exact thickness of the wall plus internal insulation and paneling,
I was able to calculate an internal position for a hole drilled
downwards at an angle of about 25 degrees or so relative to the wall
surface. I used a long, thinner SDS drill to make the initial hole
and then a 16mm one to complete it, thus avoiding breakout of the brick
on the outside. However, I did chip away a slight groove below the
hole on the outside to take the curve of the cable.
Threading the cable through proved to be a challenge. Even this stiff
cable tends to bend. I cut the SWA well over length and then cut
about 500mm of outer insulation from the end. The steel wires were
then snipped off. From inside, a piece of 15mm copper tube was fed
downwards through the hole to the outside. The inner insulated bundle
of conductors fits neatly inside the tube so can be thread upwards.
I put a layer of tape where the outer insulation had been cut to avoid
snagging. The tube could then be withdrawn in stages as the SWA was
fed inwards and upwards through the wall.
Finally, the SWA was terminated at a box inside as before, with a short
length of 20mm conduit connecting that to the centre compartment of
some 3-compartment trunking that runs around all the walls. The final
wiring back to the CU in the workshop is then done in singles.
Obviously this part could be done in T&E if preferred.
The final result is a short length of SWA close to ground level
entering neatly through the wall.