"John Rumm" wrote in message
o.uk...
On 11/05/2010 20:40, Toby wrote:

Thanks John,

This is actually for my brother's house, and after going round there, I
realised he was being a total plank, and the cable run is just 18 meters,
I
have no idea where he got 35m from!

The garage does not have other services.

If it did have a water supply, in plastic, I assume that would not affect
things would it?

No it would not change anything. On two counts - firstly being plastic it
would not be capable of introducing a potential into an equipotential
zone, and secondly, not being TN-C-S there is no need to export the EQ
zone in any case! ;-)

(It doesn't, I was just contemplating running a plastic water pipe to my
own
garage)

The earth in the house is TN-S (Provided through the amour of the
incoming
cable).

That makes it simpler then. You could go for local TT setup in the garage
(thought it was a wooden workshop?), or at that distance with a TN-S head
end you could just export the house earth.

With the revised figures, the TLC calculator shows that 4mm cable is fine
for a 32A lighting circuit (just)!

If you are sure that is enough capacity for any future needs then go with
that (cable is cheap - laying it etc is not!)

So, with a 32A MCB in the house, would it be best to used 3 core cable
and
earth the core just at the house end, or just connect to earth both ends?

If you go with an exported earth, then use two core, and connect the
armour to earth at both ends - it will be your earth[1].

If you go with TT at the remote end, then connect the armour to earth at
the head end, but isolate it at the far end, and instead use your earth
stake for the local earth.


[1] either with metal clad box at the head end, and a metal CU at the
remote end, or the TLC piranha nuts to make a connection if using plastic
boxes/CUs. (note you should not use a metal CU if making the workshop TT)

--

Thanks John,

He is digging the trench now, but isn't sure about the depth - it will run
under some slabs of a patio, then under the back of a flower bed - am I
correct in thinking there isn't a finite depth required, it just needs to be
at a sufficient depth to avoid being damaged by any reasonably foreseeable
disturbance to the ground?

If so, would laying it just under the slabs (so it is then visible if they
are removed) would be OK (The slabs are bedded in cement, so we will
probably angle grin a channel in it), and then two spade depths at the back
of the flower bed be sufficient, with warning tape at 1 spades depth?

We would also take photos and make sure this is kept in an envelope near the
CU.

As for the termination, I would drill a hole through the wall of the house,
then mount a plastic box over this, then thread the cable in the bottom of
the box, then out the back, so no glands are used here, the box just
protects the cable from bending too sharply. Then it would run under the
kitchen cabinets to the under stairs cupboard, and terminate in a metal
adaptable box - then run the earth to the main earth terminal near the
service head, and the L&N to the CU via a short piece of round conduit.

In the garage, the SWA will terminate directly in a 4 or 5 way metal clad
CU, with a main switch, RCBO for the main radial, and MCB's for the freezer
(potentially) and an MCB for the lights - all cables run surface, in round
conduit

Does that sound OK?

The roof of the garage has some large metal triangle supports - do we need
to bond these all together, and then tie that into the earth in the CU too?

Thanks again!

Toby...