Dear Jeff: Many thanks.

It is especially interesting to learn that the expectation of encountering a
floating (no earthing) system is zero.

Expanding a bit on what you have communicated:
It appears that the transformer used between one phase of a HV 3 phase line
and distribution "wires" is 440VAC, center tapped. The distribution "wires"
to a house (or the like) are one side of the aforementioned transformer's
secondary and the transformer's center tap, which is labeled as neutral. It
is expected that another house (or the like) is fed from the other side of
the transformer's secondary and its center tap.

At the service entrance: one scheme connects the neutral to an earthing.
An alternative (called 'protective multiple earthing' (PME) ) does not
connect the neutral to an earthing, but connects exposed metal in the house
to an earthing. Wow! The latter scheme is expected in new construction.

It is not immediately clear what the advantage of the PME scheme might be.
Your caution about RF grounds is well placed.

In the North American scheme, for the last 60 or more years, a third wire is
involved - the green wire that is connected to an earthing only at the
service entrance and then to touchable surfaces of an appliance. The green
wire maintains what a human can touch at ground potential without relying on
anything else. In sub distribution boxes, the green wire is isolated from
neutral so the green wire provides a straight path for current to an
earthing.

Please correct any errors that have crept into my restatement. I once had a
G5 license and, in my radio astronomy days, spent a brief time at U. of
Manchester.

Warm regards, Mac N8TT

"Jeff" wrote in message ...

On 15/07/2012 10:10, Jeff wrote:
On 15/07/2012 03:20, J. C. Mc Laughlin wrote:
OK Gentlemen: I am now more wise. Entertainment comes in multiple
forms.

A question that is indirectly related to antennas: I was explaining to
an attorney how the common North American 60 Hz electrical system is
configured for residences (240 VAC, center taped secondary, with the
neutral connected to earth and to the green wire [only] at the service
entrance) He observed that in the UK he was told that schemes for
supplying 240 VAC 50 Hz had earthling being done, if at all, several
different ways.

So, educate us please: when we travel to the UK what are the schemes we
will find. I always used an isolation transformer that was only
connected while equipment was being used.


The UK distribution and home installation systems are paranoid about
earthing, true it can be done in several way but it it *always* done.

The primary distribution is 3 phase, the last leg being 3 phase at 440V
with 220V between each phase and neutral, normally only 1 phase is feed
to domestic premises.

Earthing is normally done locally by an earth stake at the home (or
formally bonding to water pipes, or the sheath of the incoming supply),
the neutral is bonded to earth at the sub-station and at other intervals
on the feed. Another system is where the incoming neutral conductor is
used as the earth, with no earth stake, BUT all exposed metalwork in the
home such as taps, water pipes etc have to be bonded to the earth
connection. There is a problem with this system if there is a break in
the supply neutral then the 'earth' will float to supply voltage. This
is not a problem as long as there is no connection to a real earth and
there is no path to earth hence no shock danger, and is why all exposed
conductors have to be bonded together. HOWEVER, this does pose a problem
for antenna earths as they would be a dangerous connection to a 'real'
earth with 230V between it and the local protective earth in the event
of a fault. Also if the rf earth has any sort of connection to the mains
earth there is a fire risk as that connection could carry the current
for every home between it and the neutral break.
This system is commonly known as 'protective multiple earthing' (PME)
and is common in new installations. It is imperative that you know what
system is in use before any additional rf earths are added.

Jeff


Forgot to add that except in very rural locations the feed to premises
from the sub-station is nearly always underground.

Jeff


J. C. Mc Laughlin
Michigan U.S.A.
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