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Re: [TowerTalk] US Tower damaged by lightning

To: Towertalk <>
Subject: Re: [TowerTalk] US Tower damaged by lightning
From: Grant Saviers <>
Date: Wed, 28 Apr 2010 17:32:53 -0700
List-post: <">>

Jim McDonald wrote:
> Jerry,
> My questions really were about repairing the tower, but I welcome any
> suggestions on improving the grounding.


Quite a horror story.  It seems you did a lot of smart things with the 
installation, but they weren't enough.  I'm no lightning expert but here 
are some thoughts:

An earlier post (which I can't find) referred to a consulting/lightning 
protection company that strongly advocates deep drilled (at least 3 rods 
to 30 feet plus) ground rods for tower strike protection.  From your 
descriptions of the damage, it seems to me that the strike current went 
everywhere to find ground, indicating the existing radials and ground 
rods (surprisingly) had too high a ground resistance/impedance and/or 
too much current per radial (e.g. the blown rod connection at the end of 
a radial)

Here is another appropriate reference  
Interesting take aways for me were the number and length of radials, 
current division, potential rise, conductive cement for rods, and as 
much transformer and optical isolation as is possible.  So more radials 
and rods for the tower or deep drilled rods and conductive cement seem 
appropriate.  With some googling I found some suppliers of ground rod 
enhancing materials,

I don't understand how a single point ground system can be made to work 
globally in the average residence but it does make sense to me that 
radios and PCs with peripherals have local single point grounds to 
minimize the differential ground potentials they experience.  I also 
speculate that circuits that require DC ground connections to tower 
circuits would benefit from as much series inductance as they can 
tolerate.  RFI filters with inductance in the ground lead to the tower 
side may be an easy way to provide some ground impedance and energy 
spike integration. 

Getting rid of the conductive conduit and the common grounding radial 
from tower to house/barn seems to me to be a good move as they may take 
too much of the strike current where you don't want it to go.

Lightning isn't much of a problem at my current QTH.  However, I'm 
considering a new QTH, new tower, so all this investigation has some 
value for me.  Pass on any insights you gain.

Grant KZ1W

My first boss had some "Engineering Maxims" that are appropriate:

There is no such thing as ground.
Capacitors turn voltage spikes into current spikes.
Every picofarad has a little nanohenry all its own. (my favorite)


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