Lots of people have misconceptions of what a "single point ground system"
is.
It is mainly concerned with your equipment and not the tower ground system.
As others have said, you need a good ground system at the tower to get rid
of as much energy as you can near the tower if it gets hit. But there is
still a path to the house/equipment via the coax lines from the tower so
some of the energy is going to make it to the house as it is next to
impossible to get rid of all of the energy at the tower.
The single point ground is where all of the radio equipment, phone lines,
power lines etc. share a common (single point) for connection together. That
single point is then grounded via multiple ground rods as close by as
practicable.
Ideally all equipment should have its own ground lead run directly to the
single point ground plate and not daisy chained thru other pieces of
equipment. You never want current flowing thru the equipment, in one lead
and out another. All lines going to each piece of equipment including coax,
power, phone etc. should FIRST go to the single point ground panel where
suppressors are placed especially for power lines and phone lines before
they go to each piece of equipment. The single point ground panel is there
to provide an extremely low impedance connection point between all those
connections.
During a strike that puts all lines at the same potential via the
suppressors or direct connection at the single point plate or panel.
Since all equipment has connections to it only from the single point ground
panel there is no potential difference between any lines coming or going
from the equipment.
If the power and phone grounds are a long ways or on the other side of the
house, it is best to run a power feed over to your single point ground panel
and place a suppressor on it at the panel rather than rely on a long bond
between the power panel and your single point ground panel.
So a single point ground system has nothing to do with how the tower is
grounded but only how your equipment and its inputs are grounded together.
73
Gary K4FMX
> -----Original Message-----
> From: towertalk-bounces@contesting.com [mailto:towertalk-
> bounces@contesting.com] On Behalf Of Bill Turner
> Sent: Tuesday, September 11, 2007 9:27 PM
> To: Phil Camera
> Cc: towertalk@contesting.com
> Subject: Re: [TowerTalk] Lightning Advice/Ground Potentials
>
> ORIGINAL MESSAGE:
>
> On Tue, 11 Sep 2007 20:32:08 +0000, kb9cry@comcast.net (Phil Camera)
> wrote:
>
> >OK, so now lets bond everything together, outdoors. Now when we ge the
> induced energy, everybody (grounds) all rise and fall in that voltage
> together and there is no voltage difference inside of your equipment and
> voila, no current and no zapped electronics.
> >
> >Quite simple if you think about it.
>
> ------------ REPLY FOLLOWS ------------
>
> Simple, but wrong.
>
> There is no such thing as "no voltage difference" when you are talking
> a million amps or so.
>
> Let's say your tower takes a direct hit. Lightning wants to go to
> ground. It doesn't want to go to your house, but it will if there is a
> voltage difference and a path. You may think the base of your tower
> has a zero impedance path to ground, but at a million amps, I
> guarantee the impedance is small, but not zero. Even a perfectly
> straight tower leg or piece of ground wire has some inductance and
> resistance. Because your coax and rotator lines come off the tower at
> some point above earth ground, even if only a few inches, they are
> going to see a potential difference, and it can be quite significant
> depending on your particular configuration. This potential difference
> is going to seek its own path to ground, and that path is through the
> coax/rotor wires running off to your house. At the point where those
> wires enter the house, you need to provide a second path to ground
> lest the voltage pulse get into your house and equipment and find its
> own path to ground.
>
> And this is why the concept of a "Single Point Ground" makes no sense
> to me. In the case above, there must be at least two grounds or there
> will be trouble.
>
> If there is an error in my example, please point it out.
>
> Bill W6WRT
>
>
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>
>
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