chris French wrote:

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

I have one in SE Essex if that is any use... Failing that a hire shop
may be able to help.

The reason for suggesting it was that if there was one fault of this
type it might indicate that other similar faults may be lurking. A high
voltage resistance test will shake out the ones that a multimeter will
not find.

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.

There are a number of ways of hooking these things up. Some a quite
sophisticated with main and sense electrodes, but more commonly you just
have them inline with the main earth connection to a single electrode.

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.

Using a gas pipe was not uncommon. I used to have one in my house which
just used the gas pipe as a main earth. The danger is that these days
they may end up replacing large swathes of pipe with plastic and this
can interfere with the operation of your earthing.

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.

In circumstances like that it can often work out simpler to install two
CUs fed via split tails from a main switch. You can stick an ordinary
100mA trip RCD in one for all the lights and other circuits that do not
need direct contact protection, and then have a 30mA trip RCD in a
second CU for the power circuits. Often works out cheaper than having a
£100 time delayed RCD cascaded in the same CU as the smaller threshold one.

--
Cheers,

John.

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