The Economy 7 supply to our house goes through a small box with a
built-in isolating switch and space for a single MCB. Presumably if
I can find a 20A RCBO of the same width and shape I can just substitute
this for the MCB. But if such a thing does not exist, would it be OK to
use a two pole RCBO mounted alone in a small box with no separate
isolating switch? Space is not very ample.
 It is probably a bit dubious now as it serves a single 'radial'
circuit which branches to two sockets (that I have found) and is wired
in 2.5mm^2 cable bundled with other cables and supplied through a 32A
It would have to be a new enclosure as the existing one has an integral,
non-modular switch and only space for one MCB.
That's because of the limited current demand from one socket outlet? I
haven't actually checked where they branch because we only use one
socket anyway and the other one has duct tape to avoid confusion.
ok, in which case all you can do is check the height of the available
single module RCBOs, and if not swap the box.
Yup - you are in reality just talking about a spur - just one where its
taken from origin. So the MCB will still provide fault protection for
the single 2.5mm^2 T&E, and the limitation of a single socket will
provide the overload protection. (overload protection does not *have* to
be at the origin of the circuit (although often it is)).
In reality, (and depending a bit on the installation method for the
cable) you would be hard pushed to do much damage with just a pair of
sockets even if the branch was elsewhere.
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