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Re: [TenTec] OT: Lightning and Grounds

To: Tentec <tentec@contesting.com>
Subject: Re: [TenTec] OT: Lightning and Grounds
From: Robert & Linda McGraw K4TAX <RMcGraw@Blomand.Net>
Reply-to: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Thu, 30 Jun 2005 22:00:00 -0500
List-post: <mailto:tentec@contesting.com>
Carl's comments are really the only really safe way to handle the issue. 
However, in many cases, such as remote radio installations or repeater 
installations the approach of disconnecting is not a reality.  At the same 
time, proper grounding is a reality.  I strongly subscribe to the practice 
that all grounds being served by a common electric service must be bonded 
(connected) together.

Several have asked about why disconnecting the antennas and leaving the 
ground connections caused a problem.  Look at it this way as a simple test. 
Start with 2 driven grounds say some 20 ft apart.  Measure the resistance 
between the two.  Then connect the two driven grounds together with a piece 
of #8 or larger copper and again measure the resistance between the two. 
Well of course, the connection between the two connected together will have 
a much much lower resistance.  Now then, apply ohms law, E = I*R.  You have 
2 values of R to use, one without the bond wire and one with the bond wire. 
You choose an arbitrary value of current  "I", say 100 amps.  What's the 
voltage between the two grounds?  Now, say your radio equipment is connected 
to one ground and the AC mains is the other.  Thus without being bonded 
together the difference in potential will be flowing from your radio ground, 
to your radio equipment through your 3rd pin ground or from the chassis to 
the neutral via the power transformer insulation.  Even though the equipment 
is off.  Result:  damage to the radio and if the surge is large enough, 
damage to the house.

In the example above I will use a R value of 25 ohms for the resistance 
value of the un-bonded grounds and an R value of 0.1 ohm for the bonded 
system.  In each case the current is 100 amps.  The voltage between the two 
un-bonded rods would be 2500 volts and for the bonded configuration the 
voltage would be 10 volts.  Which case would you prefer?  Most power 
transformers have a test voltage rating, primary to frame of 1500 volts.

For the comment of the power company not requiring a driven ground, I don't 
think this complies with the NEC.  Perhaps someone that is more familiar 
with the NEC can contribute to the statement.  To that end, some have said 
to use the water line as long as it is metallic.  Many houses use copper 
inside but have plastic or PVC to the meter.  No ground exists in this 

I realize that this is not really along the topic of Tentec radios, but does 
apply to Tentec radios and all other brands as well.  Thanks to the 
moderator for allowing the discussion and post.  To that end, I have a nice 
paper which I have presented at several conferences and has been published 
in several journals.  It deals with "Lightning Protection for the Home and 
Station".  It is free for the asking.  It is in Microsoft Word format and 
the file size is about 175K.

If you wish further dialogue on the subject contact me direct.

Bob, K4TAX
171 Grandview Dr.
Sparta, TN 38583

----- Original Message ----- 
From: "Carl Moreschi" <n4py@earthlink.net>
To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
Sent: Thursday, June 30, 2005 9:25 PM
Subject: Re: [TenTec] OT: Lightning and Grounds

>I completely disconnect all my equipment when a storm comes.  That means
> disconnecting all my electronic equipment from the antennas, power, phone
> lines, and GROUND.
> Carl Moreschi N4PY
> Franklinton, NC
> ----- Original Message ----- 
> From: "John Rippey" <w3uls@3n.net>
> To: <tentec@contesting.com>
> Sent: Thursday, June 30, 2005 10:13 PM
> Subject: [TenTec] OT: Lightning and Grounds
>> K4TAX wrote:
>> "George, I do hope you have those driven grounds bonded to the AC mains
>> ground and all other driven grounds around the property.  Failure to do 
>> so
>> will produce a step voltage between two different ground during a near-by
>> lightning strike.  Equipment connected between the two different grounds
>> will then share the current flowing between the two different grounds.
> The
>> result is that one can observe extensive equipment damage or worse."
>> 1. I've often wondered what would happend with a lightning strike nearby
>> and everything connected together (as at my QTH): coax feed line ground
>> block; phone; AC main; AC outlet strip for radios; radios' bus bar 
>> ground.
>> This may be dumb, but why would not the electrical charge from lightning
>> come bounding into the shack via the common grounds? Disconnecting the
>> antenna leads at the radios does not seem to be a protection since the
>> radios' grounds are common with the outside grounds.
>> 2. The local power company told me a couple of years ago that the code
>> around here anyway no longer requires installation of a ground rod at the
>> Main for a new house. What gives here?
>> 73,
>> John, W3ULS
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