Don Wilhelm wrote:
residential AC power in the US - All exposed metallic components of the
electrical wiring system must be connected to the electrical safety
ground. There is an earth ground connection at the service entry point
- which is to be the only direct ground point in the system (yes, that
is also connected to the electrical neutral at that point - and at that
point only).
If the earth is connected to neutral at the building entry, that sounds
like the UK PME system, but with the variation that every house has a
real earth electrode, not just the hams'. The problem with it is that a
neutral break can cause the return current to flow through the,
relatively high resistance ground.
With the UK implementation, there are multiple earth electrodes, but not
one per property.
The UK electrical codes require all exposed metalwork (piping, etc.),
that isn't effectively insulated, to be bonded to the supply ground, not
just the metalwork of the electrical system. I think this is now
required for all installations, but PME systems have more stringent
requirements. Although its not in my summary of the UK codes, the RSGB
point out that external antennas can rise to significant voltages if the
neutral supply is broken, and should be protected as though they were
connected to the live supply.
When an additional earth ground is used (as many hams do when driving a
ground rod for the shack, antennas, etc), that ground rod must also be
connected (using heavy wire) to the entrance utility ground rod - in
fact that connection is required to comply with the National Electrical
Code.
Same in the UK.
The UK also uses a system in which the earth is run back to the
substation and physically grounded there. That's the older system, and
possibly most common.
There is more about the implications of UK PME systems for amateur radio
at
<www.rsgb.org/emc/pdfs/leaflets/emc7protectivemultipleearthingmembers.pdf>
In IEE terms, the PME system is TN-C-S. The older system is TN-S.
There is a rare configuation (TT), used for rural overhead supplies,
where each house has its own earth electrode, but these are not
connected to the neutral, which is only earthed at the sub-station. For
TT systems, RCDs are mandatory.
--
David Woolley
Emails are not formal business letters, whatever businesses may want.
RFC1855 says there should be an address here, but, in a world of spam,
that is no longer good advice, as archive address hiding may not work.
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