[TowerTalk] Proper tower grounding

[Jim Lux]

Rudy Bakalov wrote:
> Hello, I was wondering if anyone can share or point me to sources of
> info on proper tower grounding.  I am in the process of building a
> 90' galvanized steel tower and want to make sure it is properly
> engineered, including growding, before I pour the concrete for the
> foundation.
> 
> Thanks,
> 
> Rudy N2WQ
> 

Grounding for what purpose?
NEC safety (i.e. if something shorts to it)?
Lightning protection?
RF ground (i.e. it's part of a vertical antenna installation)?

These all have different objectives and ways to get there.

In general, some sort of concrete encased grounding electrode ("Ufer 
ground") will meet the first. 20 feet of suitably sized copper wire 
embedded in the concrete base does the trick and provides a handy way to 
connect to it. (The tower bolts and rebar cage can also work, too.)

A bigger wire version of the electrical code ground will go a long way 
towards meeting the lightning protection requirement, depending on what 
you want to protect against (i.e. the run of the mill 10-20kA strike, or 
the 99% percentile 300kA  monster stroke), what is connected to stuff on 
the tower, and what sort of voltage rise you can tolerate at the base of 
the tower.  Also, lightning protection is like insurance.. you have to 
decide what you can tolerate in terms of failures/equipment damage 
versus the cost and sophistication of the installation.  If it's a 
commercial 99.999% available 24/7 facility with huge consequences if 
you're down, it's a very different matter than a ham installation where 
you've got insurance to replace the gear and can tolerate a several week 
wait for the new gear to come in the mail.

For RF ground, nothing beats a radial field of some sort.

Jim, W6RMK


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