[TowerTalk] Ufer gnds/foundations

[Jim Lux]

W7CE wrote:
>> I'm not a student of Ufer grounds.  However, I HAVE engineered some
>> large towers...including a 500' self supporter.  Everyting I've
>> read says...provide a low impedance path AROUND the foundation,
>> not through it.
>>
>> Think about it...1 million amperes is going to vaporize just about
>> anything you put down there.  I've seen 8" copper strap, 1/16" thick
>> simply dissapear.  If it's inside the concrete, the expanding vapor
>> will cause cracking and structural failure.
>>
>> My sense of the Ufer ground was that it was intended to reduce
>> corrosive currents, and improve conductivity, not to handle peak
>> lightning strikes.  Perhaps I'm wrong.  I'm sure the assembled
>> expertise here can correct me.
>>
> 
> I'm certainly no expert either.  That's why I'm asking the questions.  My 
> research pointed to Ufer grounds for towers as a good solution.  Ufer 
> proponets claim that exploding concrete is a myth.  I got the impression 
> that most modern communication facilities use Ufer grounds for lightning 
> protection.
> 
> I am curious about something.  If lightning will vaporize an 8" x 1/16" 
> strap, why even bother?  That tells me that #2 solid copper wire should 
> vaporize in direct strike also, yet direct hits happen all the time and the 
> wire and equipment survive.
> 
> Regardless of which grounding system I use, I am thinking that deeper is 
> better, especially since my soil is very dry for the first 7-8 feet.  Here's 
> an interesting link that I found last night on the subject of ground rod 
> depth:

The advantage of the Ufer ground is that it makes your ground electrode 
very large in surface area.  Therefore it has low inductance (good for 
impulses), large C to the surrounding earth (good for impulses), and low 
R (good for everything).

Except in some weird cases, I would think that the tens of square feet 
of surface area in even a small concrete encased electrode will beat a 
single rod of any depth.

>