Looking at someone's consumer unit the other day, as one does, I noticed
that the earth connection from the cu was to a clamp on the lead sheath
of the incoming supply cable. This arrangement has been in place for
many years, but was almost certainly done by a previous owner as an
unofficial, untested, modification.
This is in a pre-war house, in an urban area, with underground supply,
with a couple of inches of a lead sheath visible where it emerges from a
thickly-insulated supply cable. There is a single 30mA RCD protecting
all circuits, which apparently trips readily on any neutral (or,
presumably, phase) to earth short. There's equipotential bonding in
place to the incoming gas and water pipes, and supplementary bonding in
the bathroom. All wiring is around 20-30 years old, with some later
additions, but nothing older.
The owners asked me what they should do about the earthing: leave "well"
alone? Get something (what?) tested? Throw themselves at the mercy of
their supplier, and ask him to provide an earth? Treat it as TT (with
or without an extra earth rod? They're an elderly couple, and don't
really want massive disruption.
I said I'd ask here.
- posted 12 years ago