>From http://www.engineeringtoolbox.com/electrode-potential-d_482.html
Metal Ev
----- ----
Aluminum -1.67
Zinc -0.76
Iron -0.44
Nickel -0.24
Copper +0.34
and
"Metals which are higher in the electrochemical series displace metals
which are lower in the sequence, which means when connecting two metals
the metal with lowest potential will corrode."
Corrosion is accelerated in the presence of moisture and ionic
contaminants so it depends upon your particular conditions, but it looks
like a questionable practice to me. There is almost as much voltaic
differential between aluminum and zinc (galvanizing) as there is between
copper and zinc, and there is of course a huge difference between copper
and aluminum. Then again, it's the aluminum clamp that would take the
abuse, and they would be the easiest to replace. I just question the
integrity of the connection.
I'm light years away from being on expert on any of that, though, so
maybe somebody more knowledgeable could weigh in and comment.
73,
Dave AB7E
On 4/18/2011 12:59 PM, Dick Green WC1M wrote:
> How about aluminum contacting galvanized material? I use aluminum ground
> clamps to connect my ground and Ufer wires to the tower legs.
>
> 73, Dick WC1M
>
> -----Original Message-----
> From: Jim W7RY [mailto:w7ry@inbox.com]
> Sent: Monday, April 18, 2011 1:37 AM
> To: David Gilbert; towertalk@contesting.com
> Subject: Re: [TowerTalk] grounding quesitons: Ufer, strap, exothermic welds
>
> Good info Dave... Also From the same site:
>
> http://comm-omni.com/ and their ham radio info page...
>
> Dissimilar Metals
>
> Copper should never touch galvanized material directly without proper joint
> protection. Water shedding from the copper contains ions that will wash away
>
> the galvanized (zinc) tower covering. Stainless steel can be used as a
> buffer material. However, be aware that stainless steel is not a very good
> conductor. If it is used as a buffer between copper and galvanized metals,
> the surface area of the contact should be large and the stainless steel
> should be thin. Joint compound should also be used to cover the connection
> so water can not bridge between the dissimilar metals.
>
> The above is why you want to use tinned wire (or suitable transition
> material) not bare copper when connecting to a galvanized tower.
>
>
> Their site also has some good info about cathodic protection for guy
> anchors. If you use Phillistran, (recommended) then don't ground the
> dead-man and you will have no issues.
>
> 73
> Jim W7RY
>
> --------------------------------------------------
> From: "David Gilbert"<xdavid@cis-broadband.com>
> Sent: Sunday, April 17, 2011 10:22 PM
> To:<towertalk@contesting.com>
> Subject: Re: [TowerTalk] grounding quesitons: Ufer, strap, exothermic welds
>
>>
>> a. Neither of those codes apply to a non-electrically energized
>> structure, that's why. I have, however, glanced through the Napa County
>> (where you live) regulations online, and while I didn't find anything
>> specifically mentioning tower installations, those regulations are
>> extremely comprehensive ... almost to the extreme. They even specify
>> the size wire required for bonding ham radio equipment to the SPG. I
>> would be truly astounded if Napa County did not somewhere specify that
>> the rebar cage in a tower base needed to be bonded to the tower.
>>
>> b. The instances of cracked tower bases that I've read about, and the
>> only one quoted by I.C.E., was where the tower had NOT been bonded to
>> the rebar cage ... i.e., no Ufer ground existed, or that the Ufer ground
>> was of insufficient size. In any of those three instances you speak of
>> was any sort of investigation performed to see if the tower had been
>> connected to the rebar cage? I doubt it. In fact, the existence of
>> those three cracked bases most likely demonstrates exactly why, in
>> contrast to your original advice, the tower should indeed be bonded to
>> the rebar cage. You can't blame the Ufer for the failure if the Ufer
>> didn't exist in the first place.
>>
>> c. Yeah ... it's a myth. Here's another link for your perusal .....
>> http://www.comm-omni.com/polyweb/ufertower.htm
>>
>> Dave AB7E
>>
>>
>>
>>
>> On 4/17/2011 1:55 PM, Robert Harmon wrote:
>>> 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
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> _______________________________________________
>>>>>>
>>>>>>
>>>>>>
>>>>>> _______________________________________________
>>>>>> TowerTalk mailing list
>>>>>> TowerTalk@contesting.com
>>>>>> http://lists.contesting.com/mailman/listinfo/towertalk
>>>>> _______________________________________________
>>>>>
>>>>>
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