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[Towertalk] grounding system

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Subject: [Towertalk] grounding system
From: (Carl Smidt)
Date: Mon, 29 Jul 2002 10:32:29 -0300
Tom wrote: "99% of this is how you route cables and how you wire =
things.73, Tom W8JI"

Don't be bashful Tom, tell us how in detail please. With all this talk =
about SPG's, etc., it is still hard to visualize. I do have the 'Grounds =
for lightning' and have looked at all of the web pages, but it is still =
difficult to determine what is right.

I have a 5 foot 1" by 1/4" copper bus bar running on the wall on =
stand-offs behind my equipment and the equipment grounded to it (in =
different places along its length) with webbed straps and it connected =
to my outside ground system with about 7 feet of 3/0 copper wire, but, =
no bulkhead panel.

My cables come to the house from the tower at an eight foot height, =
which is frowned upon, but it clears everything.=20

Also, if you disconnect everything, as Pete said, what do you plug the =
inside cables into when disconnected? Grounded females on the bulkhead??

Any explanations will be much appreciated. Thank you.

73,   Carl   VE9OV

  ----- Original Message -----=20
  From: Tom Rauch=20
  To: ; Pete Smith=20
  Sent: Monday, July 29, 2002 9:08 AM
  Subject: Re: [Towertalk] grounding system

  > At 05:03 PM 7/28/02 -0400, Glenn Little wrote:
  > >Acording to some data that I got from a surge suppressor company
  > >concerning lightning induced voltages, a lightning strike one Km =
  > >will induce 200 volts per meter of wire.  The second floor of you
  > >house appears to be about 10 feet or about 3 meters above actual
  > >ground. That three meter ground wire could have 600 volts on it =
  > >a strike one Km away.  If the strike is 100 meters away, the figure
  > >goes to 1KV per meter of wire.
  > These numbers seem a bit extreme, or at least a bit categorical.  =
  > many times have you seen a lightning bolt and counted less than 3
  > before the thunder came.  Did it fry your phone?  Your modem?  Your
  > radio?

  Part of the problem with taking things literally is people who market=20
  things always try do the best job they can in pitching the need for=20
  their devices. What we read, even though traceable to facts, are=20
  often the extreme.

  The induced voltage would be influenced by many things including what=20
  is around the conductor, the impedances loading the conductor, the=20
  density and angle of the strick, the position of the conductor, and=20
  so on.

  For example the guy lines on my 300 foot tower will often "pop"=20
  across the insulators with distant flashes, yet I can have a receiver=20
  on and running and connected to that tower without ANY lightning=20
  protection and nothing is hurt.

  There is a lot of available potential across an open circuit with a=20
  conductor high and in the clear, but not much current available to=20
  drive any load. Voltage decreases dramatically even with extremely=20
  high values of load resistance.

  99% of all of this is how you route the wires into the house and how=20
  the connections are all made.=20

  > I suspect these numbers could represent worst case, but there are =
  > many variables (orientation of wire, neight above ground, etc.) for =
  > to believe that one voltage fits all.

  Absolutely Pete.

  If that were true, I'd be in deep "poo" here. I have 4 or 5 miles of=20
  antenna wire spread over a half-mile square area, and 100-300 foot=20
  tall antennas. I leave everything connected all the time, and don't=20
  have a single lightning arrestor in any feedline or control cable. I=20
  live next to the worse area in the USA for lightning, we have=20
  afternoon thunderstorms like clockwork during the summer.

  99% of this is how you route cables and how you wire things.73, Tom=20

  Self Supporting Towers, Wireless Weather Stations, see web site: =
  Call 888-333-9041 to place your order, mention you saw this ad and =
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