[TowerTalk] concrete and lightning

[Gary Schafer]

jimjarvis at comcast.net wrote:
> I was responsible for a 500' self supported installation,
> AM/FM/commercial tenants,  and significant effort was placed on routing strike current away from the foundation
> concrete.   That stick gets hit 8-10 times a year, with no
> damage, and it's been up since 1979.  
> 
> The polyphaser site indicates that concrete will absorb moisture, and release it slowly.   Depending on whether there is a good conductive path through the concrete... j bolts or welded rebar cage....you might get current to ground that way...or, if the cage system doesn't touch earth below th e foundation,  strike current would have to flow through the concrete alone...producing added heat.  
> 
> While no one can say for sure what will happen, were it my tower, I'd have 3" strap routed from the tower legs to a dissipative ground, above and around the foundation, and then a radial/strap/groundrod system beyond that.
> 
> This is particularly true if I had a fixed height tower attached to my home.  I'd want to provide a nice, low impedance path the other way.    Personal preference at present is for crankup poles that live down.   Let the trees take the big hits.  
> 
> FWIW.  
> 73/n2ea


If you don't want any strike energy to go through the concrete base then 
you better not have any J bolts in the concrete attached to the tower. :>)

Part of the energy is going to go through the concrete whether you like 
it or not. The trick is to have other adequate grounding in addition to 
the concrete.

73
Gary  K4FMX