In article ,
wrote:
I too am a bit perturbed by the apparent setup, with both an
olde-worlde voltage-operated earth leakage breaker, and a
whole-house current-balance one downstream. And as both Nick T
and Dave P have suggested, I'd want to ditch the voltage-operated
item.

The RCCB in the CU only feeds the three ring mains and the shower.
The appliances with fixed wiring (cooker, c/heating boiler,
immersion, lights, etc), are not on that 30mA RCCB and their
possible earth leakages would be detected by the old Chilton.
It makes a sort of sense.

Since your hassles have started after the supply co's mods,
I'd start with a friendly call to them.

Yes, I got them back in last week. Three men, two vans and
a serious inspection from the pole up to the Chilton. That's
the limit of their responsibility (when for free).

They confirmed what I already thought.... they had simply
replaced a two-wire feed with another two-wire feed, but
in one cable instead of two. Their opinion was that the
fault was almost certainly in our RCCB, or downstream of it.

So I hacked an old portable RCCB into a differential current
sensor, and have been going around the house looking for
possible (multiple) perps.

The electric kettle is known to have (apparently) tripped the
RCCB at point of switchoff and it is that stupid design where
actual steam is used to heat the bimetallic element. I boiled
it a couple of times, but it only showed a differential current
of less than 1mA. It's a bit mucky inside the handle so that
one is still a maybe for an occasional trip.

Other appliances, mini oven, w/machine, tumble drier, Henry,
all show a tiny differential current, of between 0.0 and 0.5mA.
The two fridge-freezers haven't been tested yet.

The biggest perp (oh buggerit!) is this computer system. It
has a differential current of 1.3mA. And (wait for it) the
little mains filter that powers the modem actually has a VDR
across Line-Earth. I can only think that fitting a VDR in
that apparently daft place is for it to conduct whenever there
is an overvoltage surge on the mains, which would deliberately
trip the RCCB.

The number of nuisance trips have reduced over the last few
days (to zero yesterday). This may (or may not) be due to two
changes made. That VDR across L-E has been removed, and the
soil around the earthing rod has been thoroughly wetted (this
is a clay soil, which I know to be bone dry down to at least
3ft, with major cracks running through it).

Touch wood.....

Thanks for all the suggestions.

--
Tony Williams. Change "nospam" to "ledelec" to email.