"jim_in_sussex" wrote in message
om...
Planning to bring my garage supply (which has a workshop section) up
to date in Christmas week. (last legal throw before part P)
A thread ran a few weeks back on running a supply cable from a house
to a (detached) garage & SWA cable was suggested. To take up that
suggestion advice is needed as it is a long time since I used SWA
cable (& then only once).
1. Rating: It would be buried (as per above thread) about 450mm
(18ins) underground (hard drive/path) - about 4m as the crow flies,
but 7m-12m after deviations round, up & down. Is it correct to use
IEE table 4D1A/ref method 1? (the illustrations for method 1 don't
refer specifically to underground use).
2. Ducting: Instead of burying it in bare soil it looks more sensible
to run it inside a duct, but attempts to source underground ducting
have failed. Does anyone know of a source, or failing that, could
semi-flexible 40mm waste pipe be used? If SWA is ducted, how does it
affect current rating?
3. Termination: The house end is no problem as that connects into a
metal enclosure which I know how to connect, but how do you connect
the garage end into a standard plastic consumer unit? Is there a
special gland for this? Or do you connect into a service block of
some type & then run the last 12 ins or so in tails?
I bought a metal enclosure box, one with knockout holes in it IIRC, and used
it as a cable changing box. If you buy the SWA cable glands you will be able
to bend the steel armouring back over the tapered collet thingy ( need to
trim it just right though ), and screw the gland together tight, compressing
the steel armouring and thus getting what I believe to be a very good
bonding. I think the cable gland kits also come with a terminal washer,
which I assembled onto the gland as I screwed it into the cable-changing box
with the nut that is supplied, and soldered a wire onto the terminal washer
, the other end of the wire going to a stud on the box, sort of belt and
braces really. I used a metal cable-changing box at both ends actually, as I
didn't consider the pvc boxes to be strong enough to take the rather stiff
SWA to, and with metal you get a direct earth bond as well. Use some heavy
duty terminal block inside the CCB to connect the cables together, at least,
that's how I did it. You will need a grommet for the PVC cable as it exits
the ccb.
Andy.
4. Earthing: I'm not completely happy about relying on a non-copper
earth (ie the steel armour). Instead can I use 3 core SWA & use the
3rd core as earth to supplement the armour? Common advice seems to
be to avoid using the house earth, but if possible I'd like to avoid
the work involved in installing an earth rod. The house supply is
100amp PME/TN-C-S.
5. Cable size: nominally 6mmsq cable is adequate for the garage load
(ring + freezer radial + lights), but am wondering about using a
larger cable - eg 16mmsq. There'd be 2 benefits - much lower volt
drop, plus less light flicker when a machine starts. Relative to the
whole project the extra cost is small, but are there any practical
snags? Does anyone know the outside diameter of these cables?
6. Finally looking up the ratings for these cables in the IEE regs &
comparing with the TLC catalog, why the differences? eg TLC show swa
16mmsq 2 core (6942x) as 91amps, IEE table 4D4A shows 89amps. In fact
most cable amp values given by TLC are lower than the IEE tables
give.
Many thanks for all help offered.
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