I have a workshop with its own small fusebox. There are two double
sockets wired like this with 2.5mm^2 T&E:
Fusebox (30A fuse) -> T&E -> first double socket -> T&E -> second socket.
Is there any reason I shouldn't continue the circuit from the last socket
back to the fusebox (adding the odd socket here and there) to turn it into
The existing cable is neatly clipped to the wall near the ceiling, and comes
down vertically for each socket at chest height. (The walls are bare brick)
Is that "properly protected", or should it be shielded?
Thanks for your answer!
No - that should be fine.
In fact I would suggets that you _should_ extend to a ring since you
are quite likely to exceed the current limit for the cable before the
fuse blows should a fault occur (a 16A or 20A fuse would be more normal
on a radial circuit like this). As a ring however, the 30A fuse will be
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
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).
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.
The 30A MCB (or is it a fuse?) in the garage is, as you say,
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.
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.
Is the wiring in the garage and workshop protected by an RCD? It
certainly should be. The neatest solution (if it isn't protected)
would be a combined 20 amp RCD/MCB in the garage CU.
That might total more than 20 amps but are you likely to have both on
at the same time? Assuming 3kw (12 amps) for the washing machine and
dryer then a 1kw fire would be fine, a 2kW one would be marginal.
Assuming the feed to that point is OK, yes. In fact since there's a
30 amp fuse in the house protecting the feed the garage CU is possibly
redundanat though it's probably worth keeping it. I think (as I said
before) I'd get rid of the workshop CU and keep the garage one with
the MCBs as they will give you discrimination with the feed being from
a 30 amp fuse in the house.
In fact, you must do this to make it compliant. A 2.5mm radial clipped
direct should be fused at 20A. A 2.5mm ring can be fused at 30A. Better
still, use a B32A RCBO instead of a fuse. Much safer, particularly for power
Actually, thinking about it, it might just be regarded as compliant anyway
(although certainly not best practice). Because you are allowed to assume
13A from a double socket, the maximum current flowing can be assumed to be
below 26A. A single 2.5mm clipped direct can carry this. It is still vastly
superior to fold back into a ring.
All I'd say is, the best and safest way to go is to take a proper switched
sub main from the house and make the consumer units in the outbuildings a
separate installation in their own right. That way, anything happening in
the outbuildings will not have as big an impact on the house system.
But that's just me. :-))
No, the general rule is to assume 20 A load on a double socket (per the BS
1363 test requirement). That stacks up with the 'double socket ton a 2.5
mm^2 unfused spur' rule for standard final circuits.
In the current case in question it's unlikely that more than 5 kW would be
required overall and I'd recommend changing the fuse to 20 A.
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