[TowerTalk] Fwd: Fwd: tower grounding

Mon Sep 1 11:03:08 EDT 2008

Now I wonder: The concrete is conducting due to water content and then  we 
drive in a few grounding rod and connect them to the tower. Knowing the rod  are 
make with a copper layer and the rebar are made of steel, isn't there a big  
risk of electrolytic corrosion? I never heard that to be a problem. Is the  
high pH the protecting factor?

I know concrete is the insulator between railroad tracks. You use the  fact 
that the wheels connect the tracks as a mean to check where a train is. I  
suspected though that where were some conductivity although I guess it may not  be 
considered enough as a good grounding for a lightning strike.

Hans, N2JFS

____________________________________
 From: wa2puq at frontiernet.net
To: HansLG at aol.com
Sent: 9/1/2008 9:08:51  A.M. Eastern Daylight Time
Subj: Re: [TowerTalk] Fwd: tower  grounding

Well, actually that question was answered by a guy in the 40's  name of Ufer.
It was found that the moisture in the concrete made it a very  effective 
coupler from the bonded re-bar cage, which was also bonded to the  tower, to the 
surrounding earth.
IIRC, the story is that it was first used as a method of  protecting military 
explosive bunkers and then extended to tower grounding by  Mr. Ufer who was, 
I believe, an FCC engineer.
There were concerns raised by some about the concrete block  possibly being 
blown apart by the power of the lightning bolt, but that was  found to be due 
to poor connections within the re-bar cage or to the tower  itself causing high 
heat and steam at the points of failure.  Also  concerns were raised about 
the concrete surrounding the re-bar rotting it  out.  But, since the pH of 
concrete is high (a base rather than an  acidic) corrosion did not occur (couldn't 
use it in buildings and bridges if  it did).  
I saw evidence of this firsthand some years ago.  An 80 foot  free standing 
commercial tower fell over because of corrosion where it entered  the block.  
BUT, what actually did it in was the layer of soil (dirt  complete with some 
wild flowers growing there) which had been allowed to  accumulate on TOP of that 
block, the top surface of which was slightly below  grade... a word to the 
wise out there... hint, hint!
One other consideration.  Any ground rods driven to augment  the Ufer 
grounded tower need to be driven at a distance to the block of TWICE  their length so 
as to be far enough away that the strike energy will be low  enough in their 
vicinity that they will actually add to the dissipative  effect.  Any closer 
and they'll be swamped out by the field at the tower  base.
Best way to visualize the earth surrounding the tower is as a big  sponge 
already filled with water.  Splash in some more and the water will  initially 
mound up at the pour point and then run off through the sponge... so  the same 
with the strike energy.  
The polyphaser website has tons of info, much of which came from  their own 
investigation on the subject.  I've used it... it  works!

73, Stan

----- Original Message -----  
From: _HansLG at aol.com_ (mailto:HansLG at aol.com)   
To: _towertalk at contesting.com_ (mailto:towertalk at contesting.com)  
Sent: Monday, September 01, 2008 2:56 AM
Subject: [TowerTalk] Fwd: tower grounding

Hi Dragonsong,

I believe the rebar cage will be  totally isolated from ground as it is  
surrounded by concrete. The  concrete is a relative good electric insulator 
and  
will therefor not  be good for grounding the tower. You have to add grounding 

rods  outside the lump of cement holding your tower in place.

There is  plenty of information of the "best way" to ground the tower. Two,   
three grounding rod driven 8 feet into ground is, I believe,  considered  
acceptable grounding for lightning strikes. When it comes  to RF grounding 
the  field 
is open for suggestions. Little depending  on the surrounding ground I,  
myself, believe in radials stretch just  above or on the surface of ground. 
Other  
folks believe the radials  have to be buried or left several feet  above 
ground. 
The length and  amount of radial is a science by itself  and I think the 
advice is:"  The more the better", up to some point that varies  between 15 
to 60  
radial.

Have fun with the tower and stay safe. K1TTT has some  serious safety  
warnings on his web site that you should look  at.

73 de,

Hans, N2JFS

____________________________________
From: _dragonsong at sbcglobal.net_ (mailto:dragonsong at sbcglobal.net) 
To: _towertalk at contesting.com_ (mailto:towertalk at contesting.com) 
Sent:   8/31/2008 11:06:21 P.M. Eastern Daylight Time
Subj: [TowerTalk] tower   grounding

First I want to thank all of you for the info  so  freely dispersed on this 
reflector. I've learned a lot in just  the month I've  been getting the 
discussions.

Now then, I just  today made a deal for my  very first tower. It seems to be 
a 
bit over  a Rohn 25 size but not quite a  Rohn 30. It's about 60 feet in 
length  and will be bolted to the house and set  in a rebar and concrete cage 

footing.

My questions are these, is it  possible to use the  rebar cage as a part of 
the grounding system for this  tower?   And, if so, what is the best manner 
of 
making that grounding   connection?

Thanks up front for your consideration and   responses.

Tearlach de   w8sco

There's nae man sae deif  as  he tha' winna   hear.
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