[TowerTalk] tower & antenna project questions

[jimlux]

Jan Wise wrote:
> I am not sure, but I think if you look at the Hand Book It will state that you do not want the tower or anything else to be grounded that goes through concrete. The reason being that a hit from lightning 
> Will cause the concrete to explode. If I am wrong someone please let me know !

not in the handbook.

in fact, the preferred grounding method is the concrete encased 
grounding electrode (aka a Ufer ground, named after Herb Ufer, who 
developed it for grounding ammunition storage buildings)

spalling from lightning occurs when you have rebar or a bolt that comes 
through the surface of the concrete, and then has corroded, so there's a 
thin gap between conductor and concrete.  When the lightning hits, the 
water in the gap boils, forming steam, which spalls or fractures the 
concrete.

You can do a quick calculation and see that even 100kA through a piece 
of fairly small diameter wire just isn't going to heat it enough to 
cause a problem.  ANd, if there is sufficient contact area between wire 
and concrete, the current density through the interface is low enough 
that the heating in the concrete is small.  It's only when you have the 
partial connection through a gap of water (which has high resistance) 
that there's a problem.