Carl, if I may a couple of suggestions based on your
comments of your system and my limited(but always
learning) knowledge. First, the connection between your
equipment ground and the outdoor ground should be a low
impedance ground. I'd recommend using #4 welding cable
(it's what I use) rather than the 3/0 cable. The welding
cable is made up of about 500 strands of 30awg wire. If
you do the calculation, you'll see that it has more
surface area (electron flow on the outside of a wire's
surface) than the larger but fewer strands of the 3/0).
Second, hopefully after you've run the cables from the
towers, at whatever height above ground, it is best to
drop them to the ground to your SPG and then route then
up again to your house entrance. If one doesn't do
that, based on my knowledge, you could end up with
energy in your residence. Phil KB9CRY
> 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.
>
> 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 -----
> From: Tom Rauch
> To: towertalk@contesting.com ; Pete Smith
> 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 away
> > >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 from
> > >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. How
> > 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
> things always try do the best job they can in pitching the need for
> their devices. What we read, even though traceable to facts, are
> often the extreme.
>
> The induced voltage would be influenced by many things including what
> is around the conductor, the impedances loading the conductor, the
> density and angle of the strick, the position of the conductor, and
> so on.
>
> For example the guy lines on my 300 foot tower will often "pop"
> across the insulators with distant flashes, yet I can have a receiver
> on and running and connected to that tower without ANY lightning
> protection and nothing is hurt.
>
> There is a lot of available potential across an open circuit with a
> conductor high and in the clear, but not much current available to
> drive any load. Voltage decreases dramatically even with extremely
> high values of load resistance.
>
> 99% of all of this is how you route the wires into the house and how
> the connections are all made.
>
> > I suspect these numbers could represent worst case, but there are too
> > many variables (orientation of wire, neight above ground, etc.) for me
> > 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
> antenna wire spread over a half-mile square area, and 100-300 foot
> tall antennas. I leave everything connected all the time, and don't
> have a single lightning arrestor in any feedline or control cable. I
> live next to the worse area in the USA for lightning, we have
> afternoon thunderstorms like clockwork during the summer.
>
> 99% of this is how you route cables and how you wire things.73, Tom
> W8JI
> W8JI@contesting.com
>
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