David,
Having to study the National Electrical Code prior to building and
wiring my house, I can talk a bit about the safety grounding for
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).
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.
Under fault conditions, the use of an earth ground that is *not*
connected back to the service entry ground can produce dangerous
voltages between the extra ground and parts of the electrical system.
73,
Don W3FPR
David Woolley wrote:
Modern electrical installations, at least in the UK, and I think also
in the US, often use a system called Protective Multiple Earthing.
With this all exposed metal work in a building should be connected
together and to the mains ground wire, but will not be connected to
the actual earth at the property boundary (it will be connected to
mains neutral). If you have this sort of installation, you must not
connect anything to true earth unless you are prepared to assume that
you are connecting it to mains live, as, in some fault conditions, the
difference between the true earth and mains earth voltage can be the
full supply voltage.
(Such installations also require special consideration with respect to
antennas and functional (RF) earths.)
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