Dave,
Wow, did I hit a nerve ? Didn't mean to stir up deep rooted
feelings on this subject.
Lets take one thing at a time. Our local building code does not specify
connecting the tower to the rebar cage. It is also not required in the national
Uniform Building Code or the NEC.
In building department inspections I have seen three separate instances of
cracked concrete tower footings caused by lightning strikes. Two common
denominators in each of these was the lack of tower grounding to a ground
rod(s),
and a required building permit was not attained (which would have prevented
this)
Urban myth ? hihi
Bob
K6UJ
On Apr 17, 2011, at 11:06 AM, David Gilbert wrote:
>
> 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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