On 17 Dec 2004 14:59:49 -0800, (jim_in_sussex) wrote:

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?

SWA is designed to be buried - save the ducting for phone, network, doorbell, whatever. Remember to
run some string through for future pulls.

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?

You can get metal glands with tags for terminating to the armour.

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.
That's what I did - use the 3rd as earth, but also earth the SWA, in case it ever gets a
spade/digger through it..!

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?

I think 16 would be a nightmare to handle - the bend radius is probably of the order of a foot or
two. Maybe split the difference and use 10.