You also have many thousands of ham radio towers in northwest 7 land
with either Ufer grounds or embedded tower bases. You tell me how many
of them have exploded during lightning strikes, and how that justifies
the admonition to "never encase a ground rod in a tower base".
I once did an extensive internet search trying to find documented
examples of concrete structures that had exploded from the inside out
due to internal grounded conductors. I couldn't find a single one.
Maybe you can find one, and if so I'd like to see the link. I did find
several instances of damage to concrete structures from lightning hits,
but all of them had external damage from simple lightning strikes. Most
other damage was attributed to the fact that there wasn't any grounding
at all ... i.e., an ungrounded structure on top of a concrete base.
From a theoretical point of view, I could picture a discharge causing
more damage from insufficient metal in the concrete rather than too
much. Spread the current ... minimize the heat buildup. If you want to
argue that a single ground rod in a concrete base is a poor idea, OK ...
I can buy that. But these other blanket statements are garbage science.
Dave AB7E
On 4/17/2017 10:45 PM, Rick Dettinger wrote:
A Uber ground was developed for dry areas during WW2. In damp areas, the
concrete can do just what happened in the concrete pole test.
Per Wikipedia article:
"A disadvantage of Ufer grounds is that the moisture in the concrete can flash
into steam during a lightning strike or similar high energy fault condition. This
can crack the surrounding concrete and damage the building foundation.”
We have plenty of damp soil in northwest 7 land.
Best,
Rick
On Apr 17, 2017, at 9:57 PM, David Gilbert <xda...@cis-broadband.com> wrote:
That isn't even close to being the same condition and only serves to help
perpetuate a stupid myth that refuses to die among the ill informed. Anyone
that doesn't understand that a Ufer ground is essentially multiple ground rods
encased in concrete is indeed ill informed. And anyone who doesn't understand
the mechanisms and considerations behind a Ufer ground shouldn't be making
contributions to threads like this.
Sorry for the ire displayed by me here, but this stupid topic keeps surfacing
year after year in ham radio circles ... and specifically this forum ...
without the least bit of thoughtful consideration behind it. I'm tired of our
hobby, supposedly a technically based one, being subject to definitively stated
exhortations that are so demonstrably wrong.
Dave AB7E
On 4/17/2017 9:09 PM, Rick Dettinger wrote:
I don’t think its a myth. In the early 1970’s, the power company I worked for
was testing out some hollow reinforced concrete poles. There was considerable
concern by the line workers that the poles might be more dangerous to work on
than wooden poles, in the event of an accident. To check this, we installed
one of the poles in a sub station, and wrapped a 26KV 1200 amp feeder conductor
around the pole. When the station breaker was closed, the pole exploded
dramatically, with a large fireball. The results might have something to do
with moisture content in the concrete. The results convinced us to only use
the poles on transmission lines that wouldn’t be worked hot, like we did with
distribution lines. Of course, the power levels are much higher in lightening
strikes. The conduction paths should similar from encapsulated ground rods in
a tower base to Earth.
73,
Rick K7MW
On Apr 17, 2017, at 8:32 PM, Doug Renwick <ve...@sasktel.net> wrote:
That myth refuses to die. I have 5 concrete tower bases with ground rods
partially encased and never a worry about an exploding base.
Doug
-----Original Message-----
-NEVER- encase a ground rod in concrete ... especially a tower base.
As a retired 2-way radio tech, I'm aware of two towers that had to be
re-installed because of lightening strikes exploding their concrete bases.
73!
Ken - K0PP
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