[TowerTalk] spider balls.. they work

[Jim Lux]

At 10:13 AM 7/30/2004 -0400, david jordan wrote:
>Boys,
>
>This discussion occurred, on this reflector,  a few years ago.  At that 
>time a commercial manufacturer of the static dissipation devices responded 
>to similar questions, etc. Check the archives or google it and read all 
>about it.
>
>NASA uses these devices extensively at it's launch platforms in addition 
>to the more conventional means to manage lightning risk.

NASA does NOT use these devices any more.  There was a test done quite a 
few years ago (Apollo era) and after several strikes on the dissipator 
itself, extensive review, etc. they went to a more conventional "Franklin 
type" (i.e. rod, good grounding, etc.) lightning protection scheme.  They 
actually have video of lightning striking the dissipators.  In the FAA 
installations often cited by the mfrs of the dissipators the same thing is 
true.

There are also some odd things like employees of the mfr later going to 
work for the government and recommending the installation of the products 
of their former company.

I've started to collect some information on 
this.  http://home.earthlink.net/~w6rmk/lightning.htm has links

It seems that the manufacturers of the dissipators are legally very 
aggressive, having threatened lawsuits against IEEE and NFPA, among 
others.  This prompted a more thorough than usual review of the IEEE paper 
(by Mousa... google for Mousa and Lightning... it will turn 
up).  Interestingly, Mousa does say that the dissipators can have a 
beneficial effect on a certain class of discharges, but actually makes 
another kind worse, and, overall, that you're better off with a well 
designed conventional system.  Also, for what it's worth, the special class 
of discharges apparently cannot occur when the thing being discharged is 
less than 300 meters tall.


  The mfr of the dissipator tried to get a NFPA standard for the 
dissipators (as opposed to the existing NPFA 780 lightning rod standards), 
and when a huge number (probably every lightning expert in the world) of 
very knowledgable people, backed up by extensive research, said that the 
proposed standard was, in short, "bunk".




>Here are several web sites that have good descriptions of how the devices 
>are used and the expectations and performance of the devices.
>Some of you might recognize the company Nott Ltd., as they build the BB3 
>mobile screw driver antenna "http://www.nottltd.com/article.html",

Nott is combining the usefulness of static dissipators for such things as 
P-static and windblown dust/rain charging on insulated antennas, with their 
usefulness for preventing lightning strikes.

His statement: "Unfortunately, a large amount of misinformation has 
accumulated over the years, much of it now accepted as fact by virtue of 
tradition." is more true than I think he appreciated when he wrote it back 
in 1986.





>"http://www.lightningmaster.com/Broadcast-2.htm",

Is quite vague, and has several misinterpretations of lightning theory.  I 
note also an interesting statement:
"
If the dissipator acts as a lightning rod and takes a hit (all static 
dissipation systems should for designed lo withstand this possibility of 
lightning will follow the path of least impedance lo ground.
"

Doesn't fill you with confidence that that the things actually work, does it.


>"http://www.esda.org/esdbasics3.htm",

This article talks about ESD protection, where the charging source is 
limited both in physical extent, size, and duration.  A thunderstorm, 
extending over thousands of meters, with couloumbs of stored charge, and 
continuous charging currents of amps, is hardly in the same category.



>and here is one written by a fellow ham operator 
>"http://www.repeater-builder.com/rbtip/static.html".

This is describing a dissipator for P-static, which is a real problem, and 
for which fuzzy pointy things work great.

Too bad that Kevin added the totally erroneous statement:

"Although not marketed as a lightning deterrent, it is interesting to note 
that after this device has been installed, lightning will likely NOT strike 
this antenna because of the lack of ability of the antenna to build a 
counter charge where discharge from a cloud would be attracted."




>Good Luck,
>dave
>wa3gin
>
>Keith Dutson wrote:
>
>>Your subject line says "they work" but you do not describe the claim of what
>>they are supposed to do.  This is highly misleading.  Most of the posts on
>>this thread have referred to advertising that claims these devices can be
>>employed to prevent lightning strikes.  What are you claiming?
>>
>>Keith
>>
>>
>
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