[TowerTalk] Lightning Advice/Ground Potentials

[Mike Brown]

Now I am confused Gary. I thought the tower ground was tied in with 
everything else. Unless, like a friend of mine who's tower is 300 ft from 
his house. If the tower is near the house,  I thought it was supposed to be 
tied into the SPG with everything else. Using more ground rods and cable 
spaced 16ft (or twice the length of the ground rod) apart.

73, Mike K9MI


----- Original Message ----- 
From: "Gary Schafer" <garyschafer at comcast.net>
To: "'Bill Turner'" <dezrat at copper.net>
Cc: <towertalk at contesting.com>
Sent: Wednesday, September 12, 2007 03:27
Subject: Re: [TowerTalk] Lightning Advice/Ground Potentials


> 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 at contesting.com [mailto:towertalk-
>> bounces at contesting.com] On Behalf Of Bill Turner
>> Sent: Tuesday, September 11, 2007 9:27 PM
>> To: Phil Camera
>> Cc: towertalk at contesting.com
>> Subject: Re: [TowerTalk] Lightning Advice/Ground Potentials
>>
>> ORIGINAL MESSAGE:
>>
>> On Tue, 11 Sep 2007 20:32:08 +0000, kb9cry at 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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