[TowerTalk] Fwd: Fwd: tower grounding

HansLG at aol.com HansLG at aol.com
Mon Sep 1 19:37:43 EDT 2008

I am not an expert in this but find the comment about concrete  interesting. 
 From: jimlux at earthlink.net
To: HansLG at aol.com
CC:  towertalk at contesting.com
Sent: 9/1/2008 6:15:46 P.M. Eastern Daylight  Time
Subj: Re: [TowerTalk] Fwd: tower grounding

HansLG at aol.com wrote:
> 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 
> will therefor not be good for grounding the  tower. You have to add 
> rods outside the lump of  cement holding your tower in place.

This is untrue.  Concrete  (unless is specially made to have high 
resistivity, as for electric  railroads) has higher conductivity than the 
surrounding soil. Lots of  ions, it's hydrophilic, etc.

The relatively high conductivity of  concrete is the basis for the 
concrete encased grounding electrode (aka  Ufer ground) currently 
required by many jurisdictions as the primary  grounding means.  Whether 
you like it or not, the rebar cage is  electrically connected to the 
block of concrete it's imbedded in (unless  you've taken specific 
precautions against it, which almost nobody  does..)

The efficacy and durability of the Ufer ground has, by now,  been 
established by over 50 years of field experience, numerous controlled  
laboratory tests, etc.

Ensuring. I have never heard about anyone having problems with  corrosion of 
the rebar unless it gets exposed. I am a little consern about the  
electrolytic corrosion still though.  

> 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. 

Acceptable is determined by many factors, not  the least of which might 
be your local jurisdiction's rules (at least if  you want insurance on it).

>From an engineering standpoint, you need to  decide what the purpose of 
the lightning ground is (i.e. what sort of  impedance are you willing to 
accept, etc.)
I still would consider some grounding rods being better. Maybe I am  wrong 
and will correct my mind if so.

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. 
> folks believe the  radials have to be buried or left several feet  above 
>  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.

I would say more a craft or art, than  a science.  For most situations, 
the soil properties are not well  known enough to actually model the 
behavior in detail. So you keep adding  wire until the performance 
doesn't improve, or you run out of money, or  you get tired of trenching.
So true,

Hans  N2JFS  

**************It's only a deal if it's where you want to go. Find your travel 
deal here.      

More information about the TowerTalk mailing list