Last week we had a minor? change made to the supply wires coming
into the house. The electricity company changed the supply wires
(from their pole to our incoming fuse) from the 1970's twin wires
to a modern single coaxial supply wire. The distance is about
30-40 yards.

Before the change I can't remember the last time the RCCB tripped.

After the change we now have permanent tripping, that started
on the same afternoon.

The tripping seems to be load-related, the more things we have on,
the more it is likely to trip. eg, To have a shower, (electric,
7KW), we now have to more or less turn the rest of the house off.


Note that the loadings we have on at any one time are no different
to those before the cabling change, when we did not have tripping.

It has taken me a few days to go round the house, measuring the
leakages (Megger), or selectively isolating various appliances. I
cannot find any single suspicious appliance.... except to say that
if we have enough appliances off then we do not have a trip during
a shower. Things with motors (vacuum cleaner) do seem to trigger a
trip.

L-N and N-E voltages are much the same as before the change,
242Vrms and 1-2Vrms each. Although I do feel that the 'dip'
of the lights as the shower is turned on does seem smaller
than previously.

Can anyone suggest what is going on? Could such an apparently
simple change to 30 yards of supply wiring make the trips more
sensitive? Is there any mistake they could have made?

For ref; The RCCB in the Consumer Unit is an MK LN5780, 240V
80A, with 30mA tripping current. Between the incoming fuse and
the CU is the old original trip, a Chilton "Voltage operated
Earth leakage trip, 60A Type D". The MK 30mA always trips,
and sometimes (maybe 1 in 5 times) the Chilton also trips.

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