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Static Dissipators?

Posted: Tue Jul 04, 2017 11:20 am
by Ray
Happy 4th of July to everyone. I really appreciate all of the real-world experience on this forum and I always learn something.

I just read an article in the June issue of QST written by an owner of a lightning protection company. In the article she says that static dissipator devices have been "debunked" by the NFPA. I've read several other articles about how they may be useful to more effectively dissipate the leader setup before a strike. The idea is to keep the air voltage gradient below a certain threshold so that the lightning does not have a ionized path to follow for the actual strike. It does make some sense to me if you have every seen someone touch a Van De Gaff generator and seen the person's hair rise straight up ( the hair trying to dissipate the static charge). I installed a porcupine dissipator last fall on the top of a new FM array. I've seen them on many installations, along with satellite earth station sites. What does the group think? Is a traditonal lightning rod more effective? Ray

Re: Static Dissipators?

Posted: Tue Jul 04, 2017 1:40 pm
by Deep Thought
First off, I wouldn't trust anything from someone running a "lightning protection company".

The NFPA usually involves itself with writing standards for fire prevention, and one of the big deals in industrial circles is prevention and dissipation of static charges on equipment and nearby surfaces to prevent volatile fume and dust explosions. Without the context of the "debunking" it's a bit hard to give you an informed opinion. I doubt they'd concern themselves with "lightning protection" in that scope.

Some folks in lightning-prone areas swear by "static cat" type devices but since all of the evidence is anecdotal it mostly comes down to a "belt and suspenders" approach with systematic grounding, bonding and lightning rods and dissipators. Even with all that, Thor sometimes targets bay #3 of an eight bay antenna for no good reason other than he can. :lol:

Re: Static Dissipators?

Posted: Tue Jul 04, 2017 5:04 pm
by Kelly
Agree with Mark, there may be something to Static Cats or other spine-ball devices, but it's hard to document. Most of these devices are installed on top of the tower, but that doesn't stop other parts of the tower from being struck. That said, I can't think of a tower which uses some of these devices, that has taken lightening damage, so there may be something to it.

Re: Static Dissipators?

Posted: Thu Jul 06, 2017 6:11 am
by w9wi
I've seen lightning strike the little green AT&T pedestal -- completely ignoring the 1,000-foot tower 150 feet away.

Lightning does whatever it darn well feels like doing.

Re: Static Dissipators?

Posted: Thu Jul 06, 2017 8:53 am
by RGORJANCE
Lightning-----IT IS ALIVE! It is intelligent. It evolves. Just when you think you have conquered it....it gets you in the butt!

Having had numerous intimate contacts with it since the early 1950's, I have learned that whatever you do to fight it, it keeps coming back with new and advanced tricks. Don't underestimate this evil force.....well, I can't really justify calling it evil as it does help us stay financially solvent. :shock:

Fossil

Re: Static Dissipators?

Posted: Thu Jul 06, 2017 9:54 am
by kkiddkkidd
When I am working on a site suffering from the ravages of the evil force... I tell the client that we can eliminate the minor strikes, minimize the moderate strikes and reduce the major strikes. For the mega-strikes, even the best surge protection in the world will become just that much more smoking shrapnel...
RGORJANCE wrote:
Thu Jul 06, 2017 8:53 am
Lightning-----IT IS ALIVE! It is intelligent. It evolves. Just when you think you have conquered it....it gets you in the butt!

Having had numerous intimate contacts with it since the early 1950's, I have learned that whatever you do to fight it, it keeps coming back with new and advanced tricks. Don't underestimate this evil force.....well, I can't really justify calling it evil as it does help us stay financially solvent. :shock:

Fossil

Re: Static Dissipators?

Posted: Thu Jul 06, 2017 9:57 am
by kkiddkkidd
I watched a tall (prob 400+ft) self supporting tower in FL get struck about halfway down and the lightning bolt then danced DOWN the tower and wore out the adjacent power lines and tree tops. I never observed it actually hit the top half of the tower.
w9wi wrote:
Thu Jul 06, 2017 6:11 am
I've seen lightning strike the little green AT&T pedestal -- completely ignoring the 1,000-foot tower 150 feet away.

Lightning does whatever it darn well feels like doing.

Re: Static Dissipators?

Posted: Thu Jul 06, 2017 1:57 pm
by Deep Thought
In my Southern Illinois youth we observed a lightning bolt ignoring at least a half dozen 30-foot TV antenna towers, three different power lines, a couple dozen tall-ish (30-40 foot) trees within about 250 feet of the gas line under a ditch full of water it had some sort of vendetta against. Up from the ground came a-bubblin' methane. :shock:

Re: Static Dissipators?

Posted: Thu Jul 06, 2017 7:39 pm
by rich wood
I have been putting the ERI dissipators on towers for several years now. They seem help bleed off the charge before the strike hits. The lightning rods should be in place also,, every little bit can help. Proper grounding in essential in any installation. Nautel has an excellent white paper on how to set up a site properly. See:
http://www.nautel.com/wp-content/upload ... t-1998.pdf

Re: Static Dissipators?

Posted: Mon Jul 17, 2017 1:15 pm
by radio_guru
I'll second the ERI lightning spurs. Put them on all my towers so far and the hits have been fewer and farther between. And at the same time beefed up the earthing system so the resistance would be lowest as well.

And like others have opined, lightning will go where it wants and how. So if the spurs dissipate the charge to where it hits something else other than the tower or building, then that's fine by me. Not that it will never hit us. But the goal is to simply reduce the potential differential to the point it finds a new gradient elsewhere....

RG

Re: Static Dissipators?

Posted: Tue Jul 18, 2017 5:55 am
by RFWarrior
I don't think they do a lot to prevent lightning strikes... there's a lot more physics involved there than a wire brush can solve. Where I do think they are very useful is to bleed off charge as the tower ionizes, minimizing the arcing across guy wire insulators and spark balls - intentional corona. So, for an AM tower, depending on location, they can be extremely beneficial... for FM towers, I'm not convinced.

Re: Static Dissipators?

Posted: Tue Jul 18, 2017 7:13 am
by RGORJANCE
Due to old age....here is one idea I forgot about.

Waaaayyyy back when.......WTMJ AM 620 kHz in Milwaukee had a three tower in-line array. Two short towers with a tall Franklin on the North end of the array.

They had a static problem which was treated with - as I recall - a 100,000 ohm non inductive resistor mounted across each insulator on the top set of guy wires all the way to the ground. This provided a high resistance static bleed to ground and from what their engineers told me, worked really well. This was the 5kw site that was West of Milwaukee in the Brookfield area. That was replaced with their new site which is a 50kw array.

Fossil

Re: Static Dissipators?

Posted: Tue Jul 18, 2017 8:33 pm
by ChuckG
RGORJANCE wrote:
Tue Jul 18, 2017 7:13 am

They had a static problem which was treated with - as I recall - a 100,000 ohm non inductive resistor mounted across each insulator on the top set of guy wires all the way to the ground.

I still have an AM site like that, each of the top insulators is bypassed with a large resistor. No idea of the value and I'm not climbing
up there with a DVM to check....but they do work.

Re: Static Dissipators?

Posted: Wed Jul 19, 2017 7:44 am
by kkiddkkidd
I have a number of sites with the dissipators and a number without and don't see any major difference between the two. With that said, IF I had a site that was lightning challenged, I wouldn't hesitate to add dissipators WHILE updating the grounding and surge suppression in general. They are just another lightning tool.

Most of the sites that I have w/ various brands and models of dissipators were built by myself and have very good grounding and surge protection anyway. If I were building a new site, I would almost certainly use them again, just because...