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
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.
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