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@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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