N. Thornton wrote:

A little explanation is in order. V-ELCBs are widely misundertood, and
are potentially dangerous. They work by /disconnecting/ all the house
earth wiring from earth, and measuring the V difference between real
earth and house earth wiring. Once this reaches 50v it should trip.

This means that assuming it is a v-elcb, none of your house wiring
will be earthed. V-elcbs must never be used with an electric shower.

Not much chance of that - I just put in a 35kW combi ;-)

With a v-elcb there is no current path from earth wiring to earth,
other than via the high impedance coil, so the impedance of your real
earth is immaterial. Bonding to a gas pipe is more than sufficient for
such an install as long as it is wired through the v-elcb.

Although I have not measured the impedence yet, I expect the gas main in
this case is relatively decent earth since it is fully metalic, and
passes through lots of heavy clay soil (mostly under concrete so it is
unlikely to ever dry out).

It is important to test v-elcbs frequently as a failure leaves the
householder in real danger. Realise all earthed items are connected
together, and none are connected to earth.

Probably less of an issue with no supplimentary equipotential bonding as
was common at the time the ELCB would have been instaled. Also for that
matter, the number of earthed appliances in use at the time would have
been far fewer as well.

The old earth connection may be ineffective with no v-elcb in circuit,
as it may be of high impedance and rely only on the v-elcb for
protection.

I shall demote the old connection to cross bonding only (might upgrade
the wire size while I am at it).

Theyre best replaced with more modern methods of protection. Their
only advantage is I've very rarely seen one nuisance trip. But despite
their clear risks I've yet to see them fry anyone. A bit of a bite
yes, but thats all so far.

Must admit in the ten+ years we have been here I have never had a trip
from either the ELCB or the RCD feeding the outbuildings (and yes they
do self test ok). Other than a mains halogen taking out a lighting
circuit fuse, I have never had any other fuses blow either (although
that could be related to the crummy earthing!)


--
Cheers,

John.

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