On 5/10/13 2:47 PM, Jim Brown wrote:
"Grab a case of your favorite beverage, find a comfortable spot near the
end of the runway of any major airport, and PHONE ME COLLECT when you
see an aircraft take off trailing a ground wire."
Like with spacecraft grounding systems, eh?
You can kind of get away with pouring a bit of household
60hz into the ground, but don't count on it to work for a
primary on a power line either!
Actually, we CANNOT use the EARTH as a conductor for AC power either --
the resistance is far too high to carry enough current.
There are cases where earth is used as a conductor. HVDC links often can
use an "earth return" if one of the two wires goes down. Of course, the
"ground" system (earth terminal is the preferred term here) is somewhat
more elaborate than most hams would install. Here in southern
California for the Pacific DC intertie (4.5kA at 1MV) it's a huge
network of silicon steel bars a few miles off the coast of Malibu. If
you know the area, the join between the "land" side and "sea" side cable
is under the parking lot at Gladstones 4 Fish.
They run it for testing once a month in the dead of night.
Presumably the resistance is low enough that the losses aren't intolerable.
For the same reason, the use of SEPARATE grounds for RF or for audio
with no "green wire" between the equipment is VERY unsafe -- the reason
for the safety ground is to blow a fuse if something "breaks" and causes
the chassis to be "hot," exposing people to electrical shock. The REASON
for the green wire is to blow a fuse, and if there's no green wire, only
separate ground rods, there's not enough current through the earth to
blow the fuse and remove the shock hazard.
73, Jim K9YC
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