In message , Andrew Gabriel
writes
In article ,
John Rumm writes:
chris French wrote:

I'm thinking that maybe my RCD isn't doing it's job properly? (We have a
TT earth system with just one main incoming RCD - about as old looking
as the CU) The test button works ok though.

Are you sure it is a RCD and not an older "voltage operated" ELCB?

If that's the case, then the leak could be via a water main or
similar to earth (you won't get 40A or anything like through a
VOELCB). Either this water main (or whatever) is not connected
to the house earthing (and has virtually full mains voltage on
it), or it is connected to the house earthing but has an
overlapping resistance area with the VOELCB earth rod, preventing
the VOELCB from working.

Another option is the VOELCB has become disconnected from the
house earthing, either due to an internal fault or deliberate
action (possibly to prevent tripping in the past).

Probably other options too, but those two spring to mind as
matching the symptoms described.

Beware, as you may have live metalwork around the house.


Well, thanks to everyone's help. The socket live earth fault does seem
to have been the problem. Rectified the problem, all seem to be fine
now. Replaced a couple of falling part 30-40 year old socket faceplates.

John, you suggested borrowing an insulation tester - if I had any idea
where to borrow one I might, but TBH this does seem to have been a one
off, the rest of what I've seen generally seems ok

Re your above comments Andrew, well the metal work around the house
seemed to be ok. The isn't any main bonding of the water/gad pipes at
the moment. The VOELCB seems to be connected properly, I can't see any
earth connections that bypass it. It has two 'outgoing' earth
connections.

One, to (presumably - I need to remove the base of an old climbing plant
to find it) a buried earth rod, the second looks older - connects to an
external copper pipe. This looks like an old gas pipe. It rises from the
solid kitchen floor, goes out through the wall, runs along the outside,
goes back inside to the utility room, where it terminates in what looks
like a capped off gas cock.

Anyway sorting out the meter/CU area has been on the job list for a
while. It's probably up to 40 years old, the main CU is chockerblock and
there is the typical hotpotch of extra switch fuses etc. A new bigger
CU, a main RCD, sorting out the main earth bonding etc. Probably
starting with replacing the VOELCB with an RCD to give more space for
the new CU, partly because that can go elsewhere on the mounting board -
replacing a great big F-off metal main switch - there presumably because
the house has a 3 phase supply. Though only 1 phase is used.


--
Chris French