[TowerTalk] Ground Rods into Concrete Stubs

[Ed - K0iL]

> > Thursday, August 17, 2000, 11:10:07 PM, you wrote:
> > MF> I'm in the process of getting a tower put in, a 48' Rohn HDBX.
> > MF> Is there any reason that I can't take and attach 3 ground rods to 
the BOTTOM
> > MF> of the base stubs (that are buried in the concrete)?  That would 
put them
> > MF> another 4-5 feet down.
> > MF> I am planning on also putting in some more ground rods (8 footers I 
imagine)
> > MF> in the immediate vicinity also.

A Ufer ground such as you're asking about might be more trouble than it is 
worth in my recent experience.  You may, depending on your soil 
composition, be setting yourself up for galvanic corrosion by placing 
galvanized steel in contact or even close proximity to copper rods with 
both contacting the soil.  I would NOT attach the copper ground rods 
directly to the Rohn Concrete stubs (galvanized steel), nor would I place 
galvanized rods in  place of the copper rods with additional copper rods 
near the base.  Doing so might be asking for accelerated corrosion 
problems.

For a background explanation; at work we are in the process of replacing 
guy anchors on most if not all of our commercial 300' to 500' towers due to 
galvanic reaction.  We had "C" channel guy anchors in contact with the soil 
with below grade concrete anchors.  The guys wires were grounded using 
copper ground rods per industry standards (Motorola R56).  Bad idea, 
especially in southeastern Nebraska where the soil composition accelerated 
the corrosion process.  In less than 15 years, maybe only 12, the corrosion 
caused a 1.5" hole and 4" of very thin area overall in a 6" C-channel.  You 
could flake off the steel with your fingernail.  Even in areas where the 
soil composition was less damaging, we still have so much pitting and loss 
of steel that we're replacing the anchors anyway.  Some anchors where added 
during upgrades less than 4 years ago and they already show signs of 
pitting as well.

To counter this problem on the new legs, we're installing sacrificial 
anodes (magnesium I think) and coating the new anchors with a roofing 
compound so they will not directly contact the soil.  Also in the problem 
soil areas we are using galvanized ground rods to ground the guys.  You can 
read about galvanic corrosion on Anchorguard's web page at 
http://www.anchorguard.com if you like.  Not associated with them, just 
found the site very informative on the subject.  There are other vendors 
selling these as well.  Good luck with your HDBX tower.

73,
de ed -K0iL
k0il@arrl.net


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