I don't know whether I would call that "extensive" damage but whatever...
I have my own photos of me standing next to this anchor, but since I can't send
attachments, here is a link:
https://en.wikipedia.org/wiki/KVLY-TV_mast#/media/File:KVLYPylon.jpeg
I didn't see any extra grounding conductors. BTW, my GPS said this was 1/4 mile
from the base of the tower :-)
I'm not saying that extra grounding isn't required or is a bad idea, just that
concrete encased steel isn't a bad idea.
Wes N7WS
On 4/18/2017 8:01 AM, Rick Dettinger wrote:
Here is an article that described a Ufer ground failure that prompted the
installation of an extensive external grounding system on a 1900’ BC tower.
http://www.radioworld.com/headlines/0045/proper-grounding-and-bonding-are-crucial/338510
The Broadcast industry doesn’t seem to put their faith in Uber grounding.
Rick
On Apr 18, 2017, at 12:25 AM, David Gilbert <[email protected]> wrote:
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 <[email protected]> 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
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