[TowerTalk] Earthing a tower

[K8RI]

On 1/2/2013 10:12 AM, Jim Lux wrote:
> On 1/1/13 8:21 PM, K8RI wrote:
>> On 12/30/2012 2:14 PM, ve4xt at mymts.net wrote:
>>> Another repetition of the exploding base myth.
>>>
>>> If concrete is so explosive, and such a poor conductor, why is it
>>> often used to assist with rod-earth connections?
>>>
>>> As well, the very existence of the Ufer ground pretty much debunks the
>>> exploding base mythology.
>>>
>>
>> The NWS even has  video showing what could be construed as the exploding
>> base and it is no myth, BUT we need to be able to separate cause from
>> hearsay.
>>
>
> Can you provide a URL or something?  I tried googling "NWS concrete
> damage lightning" etc and couldn't turn something up.

I searched on "concrete damage by lightning" in Bing.

I haven't found the one on the NWS event yet, but there is a comment 
about half way down on
http://forums.mikeholt.com/showthread.php?t=131113
by  dereckbc referring to a telecom site grounding to minimum spec.


The NWS event I was referring to was part of a Sky Warn training session 
a couple of years back, but I have little sense of time so all I can say 
for sure is that it was probably some time in the last ten years.  I've 
not found the specific photos I was referring to, but all I did find 
appear to be related to moisture getting into the metal/concrete interface.

Third row down on (Depending on your screen resolution) shows a pier pin 
tower base with a chunk blown out http://www.bing.com/images 
/search?q=concrete+damage+by+lightning&qpvt=concrete+damage+by+lightning&FORM=IGRE




>
> I did find a LOT of pictures of concrete damaged by lightning, but none
> of them were a Ufer ground.. More things like a sidewalk hit by
> lightning, or a concrete block wall with a big crack.

Likewise I only found the one tower base, but lots of structural photos.


>
>
>
>
>> I have seen pictures of concrete blown apart from lightning strikes and
>> some of those were from the NWS so I believe them.  However in those
>> cases we need to ask WHY did the concrete either blow apart, or crack so
>> badly it had to be replaced.
>
>
> Yes.. the ones I saw were not a Ufer style ground.
>
>
>
> In the course of my googling, I also learned about Bruce McCain or Max
> Mccomb (I saw both versions of the name), who was an electrical
> contractor responsible for grounding ski-lift towers in the Sierra
> Nevada. His success with the Ufer ground led to his advocating it for
> the NEC.
>
> Of course, this is hearsay so far.. haven't found the original info.
> Just "did you know about x..." kind of stuff in a forum or website.
>

I do have the one, first person account by  dereckbc referring to a 
minimum NEC spec UFER ground at a telecom site, but no photos.


>
> One common thread in all the discussions I've read where spalling did
> occur was that either
> a) it wasn't a grounding system issue.. it was somewhere else in the
> structure
> b) where it was a grounding system, everyone concerned thought that
> nothing would have done any better than the Ufer ground, and probably
> worse.

I found pretty much the same, although dereckbc did recommend that 
minimum spec was likely insufficient.  I found no instance where 
something would have been preferred over a UFER ground.

As I mentioned, it appeared that water ingress was the likely cause in 
all the  events with which I'm acquainted, whether it be as first or 
second person.

73

Roger (K8RI)


>>
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