Alistair Riddell wrote:

On Wed, 9 Mar 2005, The Natural Philosopher wrote:

I have a substation in the garden. A coaxial cable comes from that
with the neutral pretty much attached to the Earth at the transformer,
and my earth busbar goes to a stake I drove into the ground about 5ft
deep.

What do I have, and what the **** difference does it make to anything?

I am not sure, but I think that the earth and nuetral are also joined
in the meter cabinet


If the earth and neutral are combined in a single conductor right up to
the supply head then it is TN-C-S.

If there is no metallic connection between your main earth terminal and
the neutral of the supply transformer (i.e. you have a metal stake in
the ground as your sole earth connection) then it is TT.

It makes a difference because in the case of a TT supply, there is a
good chance that the earth loop impedance will be sufficiently high that
a live-earth fault in the customer's installation will not trip a
protective device (circuit breaker) quickly enough or indeed at all. It
is possible that "earthed" metalwork could be humming away at voltages
significantly above true earth potential. To mitigate against this a
Residual Current Device must be installed covering the entire installation.

Ah. Thanks for that. All makes total sense now.