I'm going to add one more comment to the discussion, and then I'm not going
to post any more on it, due to the sensitive nature of the topic.
I don't think that I can build ANYTHING reasonable that will survive a
direct hit from a stroke of lightning. The currents involved are simply too
massive. So I agree with the statement that these fixes, including
unscrewing the coax, are only effective for a nearby hit.
And, since I believe in bonding the various grounds together (and in the NEC
code), I feel it is important to note that ANY reasonable ground bonding
conductor will have a MUCH lower impedance than that of the soil. This will
certainly keep the delta V much lower than it would otherwise be.
Anyway, that's it. Gonna go back to enjoying the radio !
73 de Gary, AA2IZ
----- Original Message -----
From: "Robert & Linda McGraw K4TAX" <RMcGraw@Blomand.Net>
To: <tentec@contesting.com>
Sent: Tuesday, August 12, 2003 1:41 PM
Subject: Re: [TenTec] Another grounding question
> I regret to write openly on the reflector about the following post but due
> to the error in the statement, I feel compelled to do so. The opening
> statement is absolutely wrong!! It is very dangerous to use this approach
> to grounding. The writer stated that he cut the cut the link with a bolt
> cutter. Keep in mind that the alleged lightning stroke that hit the tower
> has already traveled through a few thousand feet of air. A few inches or
> even a few feet of open link is of no extended value for further
protection.
> It is however an invitation to big trouble.
>
> If every ground system is tied together the voltage across the ground
points
> is nearly zero volts due to the low resistance, typically less than 0.1
> ohms, provided by the common bond between the points. On the other hand,
if
> grounds are not connected, the resistance of the earth between any two
> points is several ohms to several hundred ohms. It must be understood
that
> lightning is a current source of extremely wide frequency coverage.
> Actually it is a series of pulses in a single stroke. These pulses have a
> very sharp rise time and a slow decay time thus the wide RF spectrum of
> coverage. The values of ground system inductance, ideally very low thus
the
> reason for large flat connectors, and resistance of low R materials, of a
> ground system contribute to the overall efficiency of the system.
>
> Case in point. Take two values of R being a low value typical of ground
> points bonded together and two values of R such as two or more driven
> grounds in the earth. Pick a value of current in amps and calculate the
> voltage drop across the values of R in both cases. Now decide if you want
> two grounds bonded together or two separate grounds. The voltage between
> the two example systems should tell the whole story. Low voltage, little
> damage. High voltage, lots of damage.
>
> Now, about direct strikes. It is virtually impossible to protect from a
> direct lightning strike. The total effort with regard to lightning
> protection is focused on protection from "nearby strikes" and prevention
of
> direct stroke build-up. These are the ones that cause more than 90% or
more
> of the damage and these are the ones that the population is least
protected
> from.
>
> A better understanding of lightning and the effects are best found on the
> "Lightning Safety Institute" website.
>
> For additional reading, please see the following:
> http://www.amwindow.org/tech/htm/lightning.htm
>
> Also please see the references at the end of the paper.
>
> 73
> Bob, K4TAX
>
>
> ----- Original Message -----
> From: "K Van Horn" <W7SV@sbcglobal.net>
> To: <tentec@contesting.com>
> Sent: Tuesday, August 12, 2003 10:59 AM
> Subject: Re: [TenTec] Another grounding question
>
>
> > Dear Ed and Janet,
> >
> > Do not EVER tie them together! When lightning strikes your tower, and it
> > WILL, you will have upwards of 100000 volts destroying every electrical
> > device in your home from the ground lead of your electrical system
during
> > the 15 -50 milliseconds that it takes for the voltage to bleed off into
> the
> > ground system!! Many textbooks recommend tieing these together, but they
> are
> > in ERROR!! Save yourself a lot of money and more trouble than you can
> > imagine!
> >
> > If you tie them together and you take a strike, the following is a list
of
> > what you can expect to replace:
> > (even if they are turned off at the time of the strike because the
voltage
> > is so high that it jumps the switches)
> >
> > Air Conditioner (inside and outside unit)
> > Refrigerator
> > Dishwasher
> > Oven
> > Microwave
> > Television sets
> > Amplifiers
> > Radios
> > Computers
> > Can Openers
> > Clock Radios
> > Light Bulbs
> > Doorbells
> > Stereo Amplifier and Receiver
> > Garage door opener
> > Security System
> >
> > All in all, over $20,000 in damage on two strikes 6 days apart.
Whereupon
> I
> > realized the error and cut the link out with a boltcutter and solved the
> > problem!
> >
> > Sincerely,
> >
> > Kirby
> > ----- Original Message -----
> > From: "Ed and Janet" <janed@burgoyne.com>
> > To: <tentec@contesting.com>
> > Sent: Monday, August 11, 2003 12:37 PM
> > Subject: [TenTec] Another grounding question
> >
> >
> > What is the thinking on grounding the tower ground to the ground coming
> into
> > the house at the power, 220 service entrance? Tie them together or not?
> Ed
> > _______________________________________________
> > TenTec mailing list
> > TenTec@contesting.com
> > http://lists.contesting.com/mailman/listinfo/tentec
> >
> > _______________________________________________
> > TenTec mailing list
> > TenTec@contesting.com
> > http://lists.contesting.com/mailman/listinfo/tentec
> >
>
>
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