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Old October 22nd 08, 05:55 PM posted to rec.radio.amateur.antenna
Jim Lux Jim Lux is offline
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First recorded activity by RadioBanter: Mar 2007
Posts: 801
Default Antenna ground or rig ground?

Rick wrote:
I know that's not the best way but I
don't want to run an 80 foot ground cable to the shack ground.
Thanks for all the good advice. 73 Gary N9ZSV



I see why you want to ground close to the shack for your single point
ground. This is good. But you will then have two grounds. One being the
ground outside your window and the other being the service entrance ground
with all the "green wire" grounds connected to it (the 3rd conductor in all
your ac line cords). When there is a strike there WILL be a potential
difference between these two grounds. That means for those few microseconds
they will NOT act as one ground and therefore there will be currents flowing
between these two points. You don't want this happening. The NEC code
requires you to bond your external grounds together, meaning you should run
a conductor outside your house from the shack ground to the service entrance
ground. It is a good idea to install ground rods every 16 feet along this
run.


It's not clear why you'd need ground rods along your NEC bonding jumper.
If you're trying to make it do double duty as part of a grounding
ring, maybe? But then, it's the "grounding electrode", and can't serve
as the jumper.

Depending on the distance, too, the bonding wire's not going to help
with the microseconds of transient (as the transient propagates down
that bonding wire)...

Electrical safety ground (green wire) is one thing, Lightning
dissipation is another, and common reference potential is yet another.
The first two have to be connected because of NEC. The first and third
are usually connected because of coax connectors with the shield
connected to the chassis.

But in terms of minimizing transient damage to your equipment, whether
or not it happens to be grounded isn't as important as whether all the
equipment goes up and down together. You could put it all in a metal
cage and suspend it from an insulator and let lightning hit it, without
problems. (people do this for HV measurements on tesla coils and EMP
testing)




And the same conductor should be connected to any tower ground you
have as well.




There's tons of information on this subect. The antenna email reflector
archives is a good one, as well as the QST series about 4-5 years ago.
I know you don't want to do it, but the purpose of that 80 feet of wire is
important. Without it, all of your other work could be for naught.

Rick K2XT