In article ,
wrote:
Chris wrote:

The fuse situation seems a bit unusual to me anyway: The garage is fed
from a 30A fuse in the house by a heavy duty outdoor cable. In the garage
is a small CU, with the workshop feed on a C20 MCB. Finally in the
workshop is a small CU with two circuits; the 30A socket circuit and a 15A
lighting one.

So if I understand correctly, the garage fuses are pretty pointless,
unless/until the MCB (and probably cable) in the garage are upgraded.

That does seem a bit of a 'growed like topsy' setup. It's not
particularly bad or dangerous though. The most significant problem
will be the lack of discimination between the workshop CU and the
garage CU (and/or the lighting circuit, see below).

Ok.

Given that the whole of the outside wiring is fed from a 20 amp MVB in
the garage you are OK extending the sockets wiring without making it
into a ring as a 20 MCB is the correct rating for a radial circuit of
this sort. I see little point in changing it to a ring unless you
really need to uprate the total load capability.

Ok. We may end up putting washing machine/dryer in there at some point,
as well as an electric heater, so I'll have to work out how much load
that all comes to.

The 30A MCB (or is it a fuse?) in the garage is, as you say,

There's a 30A fuse in a carrier at the house end, and a rewirable 30A
cartridge in the workshop. The garage in the middle has MCBs - not very
consistent!

superfluous but the lighting one isn't. That's my one worry about the
system, a 15 amp circuit isn't correct for lighting and most lights
are only rated to be used on 6 amp or (sometimes) 10 amp circuits.

I see. These are a pair of striplights (which need replacing anyway, but
that's another job).

Personally I'd retire the CU in the workshop, leave the power circuit
as a 20 amp radial protected by the MCB in the garage and run the
lights from an FCU with a 5 amp fuse in it.

That would certainly simplify things a bit.

If I need to up the load in the workshop, I'd then presumably need to
do something like wiring it as a ring starting and ending at the garage
CU.

Is the wiring in the garage and workshop protected by an RCD?

Yes, the garage unit is an RCD.

Thanks very much for the detailed reply!

Chris
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