I appreciate the good counsel to date. I am trying to zero in on a few
issues.
1. The problem with connecting the AC green wire to the radio room
ground and then connecting my bulkhead "SPG" to a new ground rod or
even a perimeter ground connection is that my radio installation
becomes part of the AC protective ground system for the house. That
is, any house fault or other current will partly be routed through my
radio ground system. Is that what we want? I believe the electrical
code would permit the installation of an isolation transformer where
the primary is grounded back through the house ground and the secondary
is grounded locally. That would be a serious expense for a possibly
minor benefit - but it would ensure that house ground currents would
not flow through the radio system. I suppose it's more of an issue for
industrial installations or recording studios...
2. If I install a new ground rod system near the radio room, it is
unlikely it will be as good as the water pipe ground (about 35-40 ft
distant) that is used by the house AC. Especially since I can't drive
any deep rods due to rock ledge. How do I decide if it's better to run
a low-inductance strap to the water pipe or to make as good a local
connection as I can (horizontally buried cable or rod, probably)? Of
course, some say we should do both. (More work!)
3. What's wrong with the following picture? When we develop a local
"single point ground" system, we are really defining a local ground
reference plane. If all wiring and equipment are protected by and
bonded to this plane, why do we care if there is a good earth
connection at all? (It's like living in a Faraday cage, sort of.) Even
the best ground is likely to have several ohms of DC resistance and
maybe 50 ohms of reactance at 1 MHz. Your random lightning bolt might
give your system a 1 kA surge, raising your SPG to 1-10 kV relative to
(distant) earth. The earth ground system gives the current a
controlled way to earth, but doesn't keep your SPG at zero volts. As
long as your gear is well bonded and surge protected, it may survive.
(Don't ask about the op!) Thinking this way, we conclude that the
questions about earth connections are about fire prevention & building
safety (boring!), more than saving your equipment (important!). Or are
we missing something?
73, Martin AA6E
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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