[TowerTalk] Fwd: Earthing a tower

[Hans Hammarquist]

 Anecdote or not. If you push enough current though any conductor it will "explode". (This is actually use in one type of detonators.) I don't know how much current required to crack concrete and if a direct lightning strike can be enough, but I don't think we have to worry so much about that as such a "super" strike will cause more harm in other places around the tower hit. 

I have my present house designed to take a "super" strike. I am using 3/4" copper pipes in all four corners of the house. According to the engineer, helping with this design, my house is ready for one of these "super" strikes, observed on occasions. I believe it is a lightning with a peak current of 300 kA, maybe it was even more. Anyhow, after three confirmed, direct hits in the house, I feel relatively sure I did something right.

Happy New Year everyone,

Hans - N2JFS

 

 

-----Original Message-----
From: Jim Lux <jimlux at earthlink.net>
To: towertalk <towertalk at contesting.com>
Sent: Sun, Dec 30, 2012 5:22 pm
Subject: Re: [TowerTalk] Earthing a tower


On 12/30/12 10:33 AM, Michael Mraz wrote:
> My dear old SK friend Al Caplan, who used to manage the Hy-Gain amateur
> division when it was part of Telex, was emphatic about proper grounding
> when I bought my HG-52 crankup. He said that lightning could split the
> concrete around the re-bar if the tower took a direct strike. It was a
> long time ago, but my recollection was that this nasty event actually
> occurred to some unfortunate ham who had to abandon the old foundation
> and install a new one in a different location.
>

this anecdote and ones similar come up all the time.  The short answer 
is, "not if the system was properly constructed in the first place".

If the rebar penetration of the concrete surface is incorrectly done, 
then it's a problem.  For instance, if the top of the concrete holds 
water at the steel/concrete join, it will eventually wind up inside a 
tiny crack, which then causes corrosion of the iron.  That in 
combination with water in the crack will cause spalling or cracking when 
lightning heats it up.


And when discussing "well, what it the installation isn't done right, 
then disaster strikes"... I'd contend that the odds of getting a Ufer 
done right are a whole lot higher than some of the bolt on clamp and 
grounding rod schemes I've seen over the years.

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