[TowerTalk] Conclusion: Ground Rods into Concrete

[K7LXC@aol.com]

In a message dated 08/19/2000 7:35:59 AM Pacific Daylight Time, 
mike.foerster@home.com writes:

> 1. Concrete could explode if the tower were hit by lightning.  Most agree
>  this is a myth.

    The phenomena is that the lightning arcs between the rebar pieces 
(potential differences) since they aren't bonded. It's this high temp plasma 
that causes the damage. 
>  
>  2. Any re-bar extending out of the concrete would rust and carry inside the
>  concrete and
>  affect the strength.  My initial thoughts are that this would take many
>  years to affect the structure
>  of the concrete. After reading the articles in the above, my feeling is 
that
>  it still may not affect the
>  concrete mass for many years past the service life of the antenna.
>  
    The building codes say that the rebar cannot touch the dirt because of 
the migratory rusting that takes place. In many tower bases, the rebar isn't 
structural but keeps the concrete from shrinking and cracking. 

>  3. There seems to be a valid point in sing the rebar and that the concrete
>  as a conductive ground,
>  (Ulfer ground) along with the existing ground system.  But not really
>  completely understanding the system,
>  I've opted to pass.  (I didn't find a lot on the internet with my
>  searches...)

    Ufer grounds are handy where you don't have enough room for a 
full-fledged ground system; commercial guys use them in these instances. 
Everything has to be bonded so it's out of the scope of most amateur 
installation. If you've got room for a 'standard' ground system, there's no 
reason to go to all the work of an Ufer ground. 

    BTW I've got reprints of the paper ("Protection to Keep You 
Communicating") by Roger Block of PolyPhaser that was written to address ham 
ground systems. A buck to Box 572, Woodinville, WA, 98072, will get you a 
copy. 

Cheers,    Steve    K7LXC
Tower Tech

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