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?

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.