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Re: [TowerTalk] Lightning Advice/Ground Potentials

To: <>
Subject: Re: [TowerTalk] Lightning Advice/Ground Potentials
From: "Roger (K8RI)" <>
Date: Wed, 12 Sep 2007 01:05:52 -0400
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>> There is no such thing as "no voltage difference" when you are talking

I agree a "no difference" situation id highly unlikrly, but I agree with Jim 
in you are unlikely to see any where near a million amps. 50,000 to 100,000 
for the really big monsters, or the so called "super strikes"

>> a million amps or so.
> Doubt you're going to see a million amps.  really, really big strokes
> might be 100kA, but that's in the stroke, not in some grounding wire

Even if it does hit that it's a very short duration peak (probably no more 
than 10 miliseconds or so)  with rapid rise and fall times. So the power 
disipated is considerably less than is usually expected.

> (the tower might carry that, but as soon as you start dividing the
> current up among various paths to "earth" the current in any one
> conductor gets smaller).  The peak current can also decrease because of
> the inductance of the conductors spreading the pulse out.
> Most lightning is in the 10-20 kA range.  The long duration continuing
> current that starts fires is actually in the hundreds of amps range.
> 100kA strokes are rare.

Probably less than a half percent and they tend to ocurr in the cooler 
weater. Also they are *apparently* associated with the "Sprites" reported by 

> See, e.g. M. Uman, "Lightning" or anything by Uman and Rakov in the last
> 10 years.

Iman is good, but you might find some NASA with some additional information 
on the super strikes.


Roger (K8RI)

> A lot of "lightning damage" is from induced currents, rather than direct
> conduction.  That several kiloamps with a few microsecond rise time
> flowing through the lightning down conductor has a pretty hefty magnetic
> field, and if you have a loop with a couple square meter area that
> intercepts that field connected to a sensitive circuit, it fries.  Folks
> fooling with small Marx banks, medium sized Tesla coils, and medium
> hobby Van deGraaff generators find this out real fast.  The energy in
> the "bang" is low in all these (a few joules), but they are notorious
> electronics killers at short range (garage door openers are a common
> victim).
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