[TenTec] Another grounding question

Tue Aug 12 15:15:39 EDT 2003

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 at Blomand.Net>
To: <tentec at 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 at sbcglobal.net>
> To: <tentec at 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 at burgoyne.com>
> > To: <tentec at 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
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>
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