Roger Mills wrote:

Others have suggested going out through the wall with the T&E, and joining
it to the SWA using an IP65 box mounted on the outside of the wall. That
might be easier in some ways, but I'm not sure how best to seal the T&E
cable entry into the box. Any suggestions? Do I drill the back of the box,
and align the hole with where the cable comes through the wall, and seal
round the cable with silicone sealant? Or what?

There are a few options. I would be inclined to mount the box just above
the exit point of the T&E and come up into a hole in the bottom of the
box either with one of the connical grommets/blanking plugs that you get
with some of these, or, as you suggest silicone. The very short bit of
T&E ought to be either painted or covered by a short bit of mini
trunking to protect from the UV.

If you come throught the back of the box, then silicone is probably the
best option.

Someone suggested using a different type of CU in the garage - so that if I
were to do something with a power tool which caused the RCD to trip, it
wouldn't also take out the lights. Is that what is meant by a 'split load'
CU? Any suggestions as to exactly what I would need (make, model, etc.)?

You could use a split load unit - this has a switch on the incomer, and
then a RCD positioned mid way down the bus bar. Hence you can choose
which circuits are RCD protected by placing them on the protected "side"
of the CU. However for a garrage this might be overkill since a split
load CU will probably be a dozen ways wide.

If you are exporting the earth to the garage, then you could simply use
a small CU (say 4 way)[1] with a normal incomer switch, and then fit a
type B/C MCB for the lights, and a RCBO for the power.

[1] I say 4 way to allow for a little expansion, and also give you a
better choice of RCBOs - many of which take up two ways in width (there
are single width ones that are instead double height, but not all CUs
will take those)

--
Cheers,

John.

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