[TowerTalk] grounding quesitons: Ufer, strap, exothermic welds

[David Gilbert]

Again??  Seriously?  That myth has been debunked so many times, both 
here and elsewhere, that I can't believe people are still perpetuating 
it.  I've issued this challenge several times before and nobody has ever 
responded ... please quote one single URL or technical document that 
describes a verified instance where lighting passing through a proper 
Ufer ground , or any conductive element inside a buried concrete 
structure whatsoever, cracked the concrete.  You'll find instances where 
a direct lightning hit to the OUTSIDE of a block of concrete caused 
damage (buildings, bridge abutments, etc), but not via a Ufer system of 
sufficient size and construction.

Check out the I.C.E. technical note on the subject if you don't believe 
me.  It's not difficult to find on their website ... it even uses the 
word "myth" in the subject title.

Besides ... just think about it for a second.  There are thousands of 
tower installations with a tower base buried in the concrete.  What 
would be the difference, other than beneficial spreading of the current, 
if the tower was also properly connected to the rebar cage?

Lastly, connecting the tower to the rebar cage is REQUIRED by most 
zoning regulations.

I'm honestly curious why certain urban legends, like this one, seem to 
have such staying power in ham radio.  I suspect it's because the 
purported consequences sound dramatic even if they happen to be totally 
unfounded.  The more likely they are to fire up our emotional responses 
(fear, indignation, surprise, etc) the more likely they are to be 
believed ... and worse, passed on to others.  Most of the stuff on 
Snopes is like that.  If you want to create an immortal misconception, 
be outrageous about it.

Dave   AB7E




On 4/17/2011 8:19 AM, Robert Harmon wrote:
> Mat,
>
> Sounds like a very good ground system.  I have a question on one thing.
> As part of your grounding system you mention connecting to the rebar.  I assume this is the rebar cage that
> will be cast in the concrete base.  I think this is a no,no.  A lightning strike can
> conduct thru the rebar and crack the concrete.
>
> Bob
> K6UJ
>
>
>
> On Apr 17, 2011, at 7:24 AM, Mat Eshpeter wrote:
>
>> I am about to pour concrete for the base of my HDX589 tower. I am going to go with a Ufer ground as well as the Polyphaser recommended eight 75' radials with multiple ground rods (8' rods every 16'). Location is on top of a 1600' ridge in WV and lightning is a very real concern. My QRZ web page gives a feel for the location.
>>
>> To build the Ufer ground, I am thinking about connecting a single bare 2/0 stranded copper wire to the rebar. Questions:
>> 1) is one enough?
>> 2) how do I properly connect the copper to the rebar? Is exothermic weld the only way? Any problem with dissimilar metals?
>> 3) how should the copper exit the base slab - above grade or below grade?
>>
>> Also, seems that copper strap is the preferred ground material for connecting rods together. Will 0.032" thick strap have significantly better longevity than 0.022" strap? I am refering to the strap sold by Georgia Copper.  Copper is expensive and I don't want to invest in copper that won't add any value to my installation.
>>
>> Where can I find exothermic weld products to connect copper strap to 5/8" copper clad ground rods? I am exhausted reading Harger, Erico, Terraweld info, and can only find wire-to-ground rod products, no strap-to-rod products.
>>
>> 73
>> Mat
>> KK1C
>>
>>
>>
>> 		 	   		
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