[TowerTalk] TowerTalk Digest, Vol 100, Issue 37

[Tom Cox]

This is an enduring myth, isn't it? What seems to 
get neglected from the discussions is that 
concrete is already a conductor, with or without 
the rebar. One of the points of the Ufer ground 
system is that the whole outer surface of the 
concrete, wherever it touches the ground, is a 
ground electrode, and the surface in contact with 
the ground is measured in square feet, not square 
inches.

As you said, Dave, where's the evidence for 
lightning-induced explosions, or spalling, or any 
of that, in a properly-constructed base? That's 
why it was used to protect hundreds of tons of 
munitions in lightning-prone Arizona Quonset huts 
in WWII. Thanks. Mr. Ufer.

73,
Tom, KT9OM






On 4/17/2011 2:00 PM, 
towertalk-request at contesting.com wrote:
>
> Message: 5
> Date: Sun, 17 Apr 2011 11:06:57 -0700
> From: David Gilbert<xdavid at cis-broadband.com>
> Subject: Re: [TowerTalk] grounding quesitons: Ufer, strap, exothermic
> 	welds
> To: towertalk at contesting.com
> Message-ID:<4DAB2C41.9080000 at cis-broadband.com>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
>
> 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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>>>
>>>
>>>
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> End of TowerTalk Digest, Vol 100, Issue 37
> ******************************************
>