Hi Jim,
What you have described is not a single point ground system as many may
believe. It is a multiple point ground system.
To be a true single point ground system the power and coax lines must be
referenced to exactly the same point. That is a power line must be run
over to the point / panel that the coax lines are terminated on. The
power must have protectors at that point to make sure the power is
referenced to that exact panel. All equipment grounds must be run to
that exact same panel.
Now everything is referenced to only one point.
From that one reference point you may run as many ground leads as
desired to the earth over as many paths as desired.
73
Gary K4FMX
Jim Jarvis wrote:
>
> We've beaten to death the notion of 'common' and 'gnd' being tied
> together at one point only...the service entrance. NEC is clear
> on that.
>
> What we haven't done is carefully examine what happens with our RF
> SPG, as it relates to the power ground, and the chassis grounding
> of our equipment.
>
> Picture this installation... we install a perimeter ground around the
> house using strap. We bond to 8' ground rods at each corner of the house,
> and extend strap radials outward from the perimeter, as we can. Then,
> we make ONE connection to the electrical system ground, at the service
> entrance, and add another 8' rod at that point. So far so good.
>
> Then...we run all our coaxes and control lines through a grounded panel,
> which may or may not be adjacent to the electrical service entrance.
> Then...we plug our equipment into the power system in the shack.
>
> In the event of a lightning strike, the surge impedances of the various
> paths to the equipment via RF gnd and power gnd will be different. Maybe
> a little, maybe a lot. A potential difference will be generated between the
> grounds, and across some aspect of the equipment.
>
> Can you really HAVE a single point ground? Even if the RF and power service
> entrances were immediately adjacent, and tied together with 3" strap...the
> drop circuits from each will follow different paths, and may have induced
> current on them from the primary strike...with different potentials due to
> their geometries. I still disconnect everything in the main shack.
>
> In a 24/7 broadcast installation, or amateur repeater, you clearly can't do
> that. You take reasonable precautions, and hope for the best.
>
> Thoughts/comments?
>
> n2ea
> jimjarvis@ieee.org
>
>
> _______________________________________________
>
> 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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>
_______________________________________________
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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