[TowerTalk] Lightening

[Kim Elmore]

I'm a research meteorologist at the National Severe Storms Lab in Norman, OK. I don't do Lightning research but know others that do. Here's what I know from them: 1) static porcupines don't work, 2) in order to induce a noticeably higher probability of cloud-to-ground lightning strikes, an object needs to be at least 200 ft above the average surface (not terrain). Tree tops become part of the average surface. 

Kim N5OP

"People that make music together cannot be enemies, at least as long as the music lasts." -- Paul Hindemith

> On Jun 26, 2017, at 15:50, Bob Shohet, KQ2M <kq2m at kq2m.com> wrote:
> 
> 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 at 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 at contesting.com] On Behalf Of
>> Patrick Greenlee
>> Sent: Monday, June 26, 2017 1:32 PM
>> To: towertalk at 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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