Over the past 18 years, my tall 130’ tower has been hit by lightning (not
lightening) at least four times that I know of and the shorter tower, 100’ at
least three times. Both have rebar in concrete with less then desirable
grounds due to being on ledge. In fact that 130’ has only 18” depth of
concrete at the deepest point, although I tried to compensate by making the
base bigger - much 4’ x 5’. Perhaps I have been fortunate but there have been
no issues with cracking or damage due to lightning strikes. I did use No 2
bare copper for the ground for all three legs with three – four horizontal
ground rods on each because they are mostly shallow with depth of 12’ or less
(ledge). I have no idea how effective they actually are but no issues with
anything explosive as a result of the lightning. I also use a pier pin (into
the cement) and “floating” base on each tower so the lightning has had plenty
of opportunities to affect the concrete if it was going to do so.
73
Bob KQ2M
From: Gary Schafer
Sent: Monday, June 26, 2017 4:29 PM
To: 'Patrick Greenlee' ; towertalk@contesting.com
Subject: Re: [TowerTalk] Lightening
It can happen. Several years ago I had my boat docked at a friends place and
a palm tree got hit by lightning. The concrete seawall about 10 feet away
had a large chunk blown out of it. This was a salt water canal. There was
rebar in the seawall.
It didn't do any damage to the boat except for the compass being off by
about 90 degrees for about a month and it slowly returned to normal.
In another life I used to write subcontracts for two way radio tower
installations so I saw quite a few towers mounted on and in concrete. In
that time I did see a few foundations that cracked due to lightning strikes
on the tower. However most if not all of those towers did not have auxiliary
ground rods at the base of the tower.
73
Gary K4FMX
> -----Original Message-----
> From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of
> Patrick Greenlee
> Sent: Monday, June 26, 2017 1:32 PM
> To: towertalk@contesting.com
> Subject: Re: [TowerTalk] Lightening
>
> There seems to be an urban myth in popular circulation about foundations
> being subject to being blown to bits or at least cracked open
> sufficiently for them to fail due to lightning. If this were a real
> threat wouldn't it be common experience with Ufer grounds? Can anyone
> provide a reference to a properly documented incident where lightning
> blew apart a foundation?
>
> I'd be happy to abandon my current thinking and get on board with the
> lightning blows up concrete folks it there were sufficient factual
> evidence.
>
> Patrick NJ5G
>
>
> On 6/26/17 11:23 AM, Clif Keely via TowerTalk wrote:
> > Reading through some of the comments here recently have me trying to
> recall some of the comments I have read over the years. I seem to
> recall several that spoke to using 2 or 3 ground rods on a tower which
> might not be a bad idea. I should think one of the reasons would be to
> keep the discharge energy from making steam within the concrete base and
> that explosive burst of steam, producing a lot of cracking within the
> block and with that reducing it's ability as a solid base. I have no
> research to support this but offer it only as a thought. For myself if
> I hear thunder I disconnect antenna and power cables. After that I keep
> my fingers crossed as I think lightning will do what ever it bloody well
> wishes.
> > _______________________________________________
> >
> >
> >
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>
>
>
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