wrote:

I have an old consumer unit (Wylex) with rewireable fuses.

If I decide to replace it, will I be required to use RCD/RCBOs on all
circuits (either one 'whole house' RCD, or one per way)?

Neither probably...

Whole house RCDs are not really acceptable since they offer no
discrimination in the event of a fault - one trip and you lose
everything. They are also prone to nuisance tripping as a result of
excessive combined leakage from all the circuits.

RCBOs on each circuit would certainly be acceptable, but expensive.

A more typical approach is to divide the circuits up between a number of
RCDs. Two would be a minimum, and would usually pair downstairs power
circuits with upstairs lighting circuits etc. In a flat then perhaps
power circuits on one, and lighting on the other would be more appropriate.

Note it is also still allowable to have circuits without RCD protection.
However one has to ensure that the cables are not liable to damage. That
means either burial at = 50mm or protection by earthed shielding of
some sort (e.g. metal conduit, or via a metal screened cable)

Currently, there's a single ring serving the whole flat (approx 85
sqm) and a recently installed ring serving the white goods in the
kitchen (replacing a spur bodged in by a previous occupant). Given a
fair number of switch-mode power supplies on the main ring, I'm
worried that it'll exceed the leakage budget. Would a better technical
solution in that case be to replace all the sockets on the main ring
with RCD protected sockets, is that allowed/necessary under 17th ed -

No, since an RCD protected socket does not offer any protection should
you nail through a cable supplying it.

or is all this unneccesary and the lack of RCD protection
'grandfathered' in?

If you were close to the leakage budget on your main ring, then the
answer would be to split it into two rings, and place each on a
different RCD.




--
Cheers,

John.

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