[TowerTalk] Fwd: Earthing a tower

[Jim Lux]

On 12/30/12 3:06 PM, Hans Hammarquist wrote:
>
> Anecdote or not. If you push enough current though any conductor it
> will "explode". (This is actually use in one type of detonators.)

Oddly, I have personal experience with exploding wires (not EBW 
detonators, but in other applications)...

THere's nowhere near enough *energy dissipated* in a lightning strike 
through a Ufer ground to do this.  The actual stroke is about 100 
kJ/meter & the dissipation in the stroke in air is substantially higher 
than in a grounding system.  To put 100kJ in context, TNT is about 4 
MJ/kg. about 110kJ/ounce.  So, put an ounce of TNT in a properly 
designed hole in some concrete, and you can split it or spall it.


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.

Yes..

>
> 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.

yes..

The key thing on destruction is the I^2*t (called the action).. Because 
that's related to the energy deposited