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O/T Question - What are the purpose of lightning r

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Turke Bros. Far

04-05-2007 07:16:00




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What purpose do lightning rods serve? I have them on my house and on the barn. Now Im no professor of science, but it seems to me that they would attract lightning rather that divert it.




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buickanddeere

04-05-2007 20:02:37




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 Re: O/T Question - What are the purpose of lightni in reply to Turke Bros. Farms, 04-05-2007 07:16:00  
If run ground cables with the intent of conducting the impulse current. The cable runs must be as straight as possible and certainly without sharp corners. The high currents also produce a very strong magnetic field. Lighting will often continue on straight rather than follow a cables bend or corner. If making a corner the two adjacent magnetic fields repel each other.



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KEB

04-05-2007 19:46:36




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 Where does this stuff come from??? in reply to Turke Bros. Farms, 04-05-2007 07:16:00  
Me again. Never ceases to amaze me how all this misinformation & these old wives tales continue to be propagated. Here's a couple places on the web that I know have some credibility when it comes to things like lightning. LTI is one of the foremost lightning protection and design companies in the world, to the point that they wrote the FAA's manual for protecting aircraft against the effects of lighting.

Link

Here's a link to a paper giving some background on lightning protection and the history of the technology.

Link

As I stated before, the sole purpose of a lightning rod is to guide the lightning current to ground via a "safe" path. The rod MUST be grounded in order to work, otherwise you'll end up with side flashes to who knows where on the structure. Note also that the lightning rod/ground wire does not have to survive the strike to do its job. Once the path is established, the current will continue to flow in the ionized channel even after the wire vaporizes. Obviously, you have to replace the system after this happens.

I don't want to come across as arrogant, but I'd sure like to see some reputable references providing data to support some of the mis-information being banted about here. If you can't back your statement up with references or data, then its nothing more than an opinion.

Keith

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Ultradog MN

04-05-2007 18:14:43




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 Re: O/T Question - What are the purpose of lightni in reply to Turke Bros. Farms, 04-05-2007 07:16:00  
As you all know, Ben Franklin was an early experimenter with electricity and was an advocate of putting lightning rods on buildings.
When he installed one on his own home the people in his church scoffed at him and told him that if he would only mend his ways a little he wouldn't have such a powerful fear of being struck by lightning.



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NE IA Dave

04-05-2007 16:41:48




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 Re: O/T Question - What are the purpose of lightni in reply to Turke Bros. Farms, 04-05-2007 07:16:00  
I'm confused by all the facts. The insurance companies in our area say if you have rods they must be grounded. Many ground rods have the copper wire broke off.

I have repaired a barn after a strike, and I sure do not believe a rod was intended to take a strike. The strike took on the rod on the west (top) side of a large barn. It went across the total length of the barn following the cable. It then went to the eve and towards the ground. The path was clear as the asphalt and wooden shingles looked like a mole had dug under to the sheathing. At the eves it took the corner post 8 X 10 in the barn and exploded it. There was no fire, although some charing in the path.

Right or wrong we were always told the rods took out the static electricity. It has been explained that if you hold a wire that is grounded, you can rub your feet on a carpet all day and never hear a snap of static electricity. It does make some sence, right or wrong.

Most of the older folks will not sleep at night if you remove the rods for roofing. I must say we seldom put them back on now days however it be, right or wrong.

With todays copper prices I kind of think it may be worth while to haul them away for scrap.

Regardless if they did not work, there must have been some prety good marketing skills involved.

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KEB

04-05-2007 19:56:33




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 Re: O/T Question - What are the purpose of lightni in reply to NE IA Dave, 04-05-2007 16:41:48  
Dave,

What you saw is a perfect example of what happens when a lightning rod is not properly grounded, either because the ground wire has degraded over time, been broken at some time in the past, or was never installed properly in the first place. The lightning followed the conductor until it hit a high impedance point, then flashed to the structure where it continued on to ground. Exactly what it would be expected to do if the ground wire for the lightning rod was broken.

Lightning rods have absolutely nothing to do with controlling static. You analogy of holding a grounded wire is only partly correct. Having an electrical connection to ground does keep static charges from building up on your body - in fact, people who work on sensitivie electronics use a wrist strap for that very purpose. In the case of a lightning rod on top of a building, there's very little to create static charges, basically just triboelectric charging as a result of dust being blown against the rod or building. Accumulation of charge on a relatively small object such as a lightning rod would have a negligible effect on any lightning strike.

Keith

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Billy NY

04-05-2007 15:33:43




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 Re: O/T Question - What are the purpose of lightni in reply to Turke Bros. Farms, 04-05-2007 07:16:00  
I was always fascinated by those rods and bulbs on our old barns, seems all the old farms had them around here, but I never understood how they worked. You answered your own question there, they do attract it, it's what they told me too. The company I attached a link for below, did a protection system on a 13 story building for us in '95. Very nice people, family owned, niche business, had worked out arrangements to work in NYC with I.B.E.W. local #3, was enjoyable to learn of their business. He explained the basic principal of how it works, which is kind of obvious. Apparently that special uninsulated conductor they use is, or was then only manufactured by a few companies, they had a good relationship with one, real specialty business, not a lot of people doing this work. That partcicular cable is specific for the application, must have some unique quality to it, don't recall what it was. A lot of high rise buildings have systems installed, many do not, and I'll tell you it's a darn scary thing when a storm you can't see, rolls up on you when up on a high rise in manhattan, you and 40 other guys are scrambling to get off the steel, not fun at all.

Those old Hawkeye bulbs and rods fetch a good price on e-bay, I've got one from our place, had to climb up a rickety roof to get it, it's a keepsake though.

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KEB

04-05-2007 20:04:49




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 Re: O/T Question - What are the purpose of lightni in reply to Billy NY, 04-05-2007 15:33:43  
Read the FAQ's at the company Billy has linked to. While there's some marketing slant to some of what they say, in general they're pretty much correct. I did notice one misleading statement on their home page, where they talk about lightning having voltage in excess of some large value. In terms of the effects of a lightning strike, the voltage is immaterial. What counts is the magnitude of the current pulse, which is what determines how much energy is deposited in the material the current is flowing through.

Keith

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RAB

04-06-2007 00:21:13




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 Re: O/T Question - What are the purpose of lightni in reply to KEB, 04-05-2007 20:04:49  
C"mon, Power is voltage multiplied by current. Energy is power multiplied by time. In these cases, voltages and current are the bigger numbers, but twice the duration of a pulse will still mean twice the energy (at constant power).



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KEB

04-06-2007 09:49:56




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 Re: O/T Question - What are the purpose of lightni in reply to RAB, 04-06-2007 00:21:13  
In the case of lightning, the voltage is sufficient to force a given amount of current through whatever the lightning stoke hits. The power dissipated in say a wire, is given by the square of the current times the voltage drop along the wire (i^2*r, derived from ohms law). The voltage between cloud & ground is immaterial, the only thing that matters is the voltage drop across whatever the current is flowing through. My comment above refers to the cloud to ground charge differential voltage, which as I said is immaterial in determining how much energy is deposited in the material the current is flowing through.

Lightning analysis uses a term called the "action integral", which is the current squared integrated over time, i.e., the i^2 part of the the equation above. This integral times the real part of the impedance (resistance) gives the total energy (typically in watt-seconds) deposited in the material.

Explaining all the nuances of lightning interaction with materials would require a textbook. If you want a more detailed explanation, do a seach on the web for MIL-STD-464, Electromagnetic Effects Requirements for Systems, and read the rationale for the lightning protection requirements.

Keith

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Billy NY

04-05-2007 15:49:22




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 CORRECTION in reply to Billy NY, 04-05-2007 15:33:43  
Well, wrong on that one, bad memory, they apparently don't attract lightning, thought that was what he told me, interesting stuff though.



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David in Mo

04-05-2007 11:21:17




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 Re: O/T Question - What are the purpose of lightni in reply to Turke Bros. Farms, 04-05-2007 07:16:00  
I grew up in a 2 story city house that had a dozen rods on it. Mom and Dad still live there 60 years later and the houses on either side have no rods. They both have been nailed by lightning over the years. Ours never did. Yes, rods do work, and no, the lightning does NOT hit them.



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Gary Schafer

04-05-2007 13:27:19




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 Re: O/T Question - What are the purpose of lightni in reply to David in Mo, 04-05-2007 11:21:17  
I have bought many lottery tickets over several years. Never have won the lottery. Does that prove that buying lottery tickets keeps you from getting rich? :>)
I also know several rich people that never bought a lottery ticket.

Best regards
Gary



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Gary Schafer

04-05-2007 08:58:23




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 Re: O/T Question - What are the purpose of lightni in reply to Turke Bros. Farms, 04-05-2007 07:16:00  
You are right. They are intended to attract lightning. The idea is to have the lightning hit the rods where there is a safe path to earth for the charge to go rather that hitting the roof and finding its own path thru the structure and causing a fire.

Having a lightning rod that is grounded increases the chance of a lightning strike slightly over not having it. But it is better to have a controlled discharge path to earth than to let lightning find its own way should a strike happen.

There is nothing that can be done to prevent a lightning strike. You can only take measures to direct it safely to ground should it happen.

All objects build up charge as a charged cloud approaches. The objects do not have to be metallic to build up a charge. That is why lightning can hit a wood roof just like it can a metal pole.

Some believe that a lightning rod will prevent a strike by bleeding off the charge in the surrounding area. It will not. The earth, where the rod is connected to, can supply many times the energy much faster than it can be bled off. A small ion cloud forms at the tip of the rod that would repel the lightning but the wind readily blows that ion cloud away. A better lightning rod is one with a blunt end rather than the traditional sharp point as the blunt end is less likely to attract a strike than a sharp point.

As a charged cloud moves over an area, streamers start to form from objects on or near the ground and kind of wave around in the air. Then the cloud sends out what is called a “step leaders” which is sort of like a feeler from the cloud.
The “step leader” (the predecessor to a strike) moves in approximately 150 foot steps through the air. When it gets near a streamer on the ground object it attaches and that forms a small plasma path from cloud to ground. The large strike current follows that low resistance plasma path.

Because the step leaders move in 150 foot steps (down, side ways etc.) that is why lightning doesn’t always hit the tallest object in an area. It all depends on how the step leader moves. How it moves is determined mostly by local conditions in the air. Anything that is taller than around 150 feet is just as likely to get somewhere on the side as it is to get hit at the top.

Regards
Gary

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KEB

04-05-2007 20:12:37




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 Re: O/T Question - What are the purpose of lightni in reply to Gary Schafer, 04-05-2007 08:58:23  
Gary, good description except for one point. Rods don't "attract lightning" as one would normally think of an attraction. There is a high probability that a lightning leader will attach to a grounded rod before it attaches to a lower portion of the structure (the so-called cone of protection under a lightning rod), but this effect is on applicable over a small distance. That's why you see multiple rods on buildings - if the spacing of the rods is too great compared to how far they stick up above the structure, theres a good possibility that lightning can attach to the structure between rods.

Keith

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VADAVE

04-05-2007 08:52:13




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 Re: O/T Question - What are the purpose of lightni in reply to Turke Bros. Farms, 04-05-2007 07:16:00  
Have you ever walked into a metal building where the metal touchs the ground and wondered why your cell looses signal?
The exact same reason that lightening rods work but little more simple due to the strength of the lightening.
Also when lightening is getting ready to strike the air will become charged--you can feel it.

I have absolutely no fear of my shed will be hit by lightening. Pole building with a full metal skin; metal roof touches the metal facia which in turn touchs the soffet which is in contact with the sides and that touches the ground.
Forms an excellent Faraday Shield killing a cell phone signal in the building and out about 20 feet. It also drains the charge out of the air during thunderstorms--you ask how I know that--I have experienced it. Drove in with the hiar standing up on the back of neck walked up close to the building and it just went away.
That draining of the charge prevents the strike; however should a strike occur it will ride the building skin into the ground.

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730virgil

04-05-2007 08:32:36




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 Re: O/T Question - What are the purpose of lightni in reply to Turke Bros. Farms, 04-05-2007 07:16:00  
i have heard that the balls on lighting rods where there so you knew when lighting had struck. this must have been for you weren't home when lighting struck. my dad uncle had a barn stuck by lighting and burned to ground. he built a new barn on the same spot. a few years later this barn was struck by lighting and burned to ground. he then built a third barn on that spot ,but with lighting rods as the first 2 didn't have lighting rods.

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Tim, Ohio

04-05-2007 08:32:18




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 Re: O/T Question - What are the purpose of lightni in reply to Turke Bros. Farms, 04-05-2007 07:16:00  
Do lightning rods really work?

24-Aug-2001

010824.gif

Dear Cecil:

Everyone learns about lightning rods in grade school. There is the heavy-duty kind on skyscrapers that takes the brunt of bolts and conducts them safely to ground, and the delicate, sharply pointed ones that protect residences by bleeding off electric charge and preventing strikes. Having been well schooled in skepticism by our beloved Cecil, I tried to find a scientific study showing that rods actually ward off lightning, before plunking down dollars. No luck, except for manufacturers' marketing propaganda. I've seen a scale-model village successfully protected by tiny lightning rods from a "lightning" machine. But models don't always scale up to the real world. Do houses with lightning rods actually get hit less often than houses without? --John Glenn, N.T.A. (Not The Astronaut), San Francisco
Cecil replies:

You're thinking: What a stupid question. Everybody knows lightning rods work. People wouldn't have put them on buildings for more than 250 years (lightning rods were initially proposed by Benjamin Franklin in 1749) if there weren't a sound scientific basis for them, would they?

Well . . . maybe they would, maybe they wouldn't. We need to have a little talk.

Current U.S. lightning protection standards are embodied in a document published by the National Fire Protection Association known as NFPA 780. First issued in 1904 and updated periodically since, NFPA 780 codifies the traditional lightning rod installation, in which sharpened metal "air terminals" known as Franklin rods are connected to an earth ground by means of heavy conductors. A lightning bolt strikes a Franklin rod and is carried harmlessly to earth by the grounding apparatus, sparing lives and property. Though technically voluntary, NFPA 780 has been adopted by many local jurisdictions and government agencies and is the de facto national code.

Some years ago manufacturers of a new type of lightning rod using what's called early streamer emission (ESE) technology began agitating for a new NFPA code for their product, which supposedly requires fewer air terminals that can be placed farther apart than the traditional Franklin rods. An ESE terminal, described as looking like "a chrome cantaloupe with a chrome Frisbee around it and a little sharp prong on top and mysterious portholes around the sides," uses radioactive material to send a stream of ions aloft. This supposedly provides a path for lightning and guides it harmlessly to ground.

Most research to date shows that ESEs work no better than Franklin rods and fails to justify the claim that fewer terminals can be used. In 1993 the NFPA declined to approve proposed NFPA 781, which would have set ESE standards and presumably given the ESE industry a shot in the arm. ESE makers sued, claiming NFPA 781 had just as much scientific backing as NFPA 780. In a settlement the NFPA agreed to have ESE technology reevaluated by an outside panel.

The panel confirmed that there was no scientific basis for NFPA 781. But guess what, it said. There's no scientific basis for NFPA 780 (traditional lightning rods) either.

NFPA membership voted to approve an updated 780 anyway, but the NFPA standards council overruled them and announced its intention to rescind 780 unless somebody could give them good reason not to. While the NFPA wouldn't come right out and admit it when I called, I suspect the threat of another lawsuit was in the back of everybody's mind.

Proponents of traditional lightning rods freaked. A report from the Federal Interagency Lightning Protection User Group said, in essence, Come on, everybody knows this stuff works--if you rescind NFPA 780 it'll be back to the anything-goes days of the 19th century, when lightning rod con artists abounded. But there was an unmistakable air of desperation to the group's plea. Much of the evidence was from sources like the Iowa state fire marshal's annual report from the 1920s, which talked about barn fires. After 1950 research largely ceased; people just assumed traditional lightning rods worked.

They probably do work, but maybe not as well as was once believed. Critics of 780 point out that lightning remains a largely unpredictable phenomenon and that rods merely improve your chances rather than offering guaranteed protection, as the old code assumes. (Another beef: the committee in charge of 780 includes too many lightning rod manufacturers, who have a vested interest in maintaining the status quo.)

The NFPA standards council deferred a final decision "to give proponents of NFPA 780 an adequate opportunity to set forth the claimed substantiation for traditional lightning protection systems." Comments are currently being accepted; the group will decide what to do next at its October meeting. I'm betting the sparks will fly.

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John T

04-05-2007 08:05:48




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 Re: O/T Question - What are the purpose of lightni in reply to Turke Bros. Farms, 04-05-2007 07:16:00  
They actually do work if designed n isntalled properly. When a cloud passes over with all that charge accumulation once the potential voltage between it n something on the ground is high enough current will arc jump i.e. a lightning bolt. The lightning rod system is to allow a slow gradual discharge to prevent the sudden high energy discharge strike.

John T



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Brian G. NY

04-05-2007 07:52:14




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 Re: O/T Question - What are the purpose of lightni in reply to Turke Bros. Farms, 04-05-2007 07:16:00  
There was lightning protection on every building (including the chicken house) at a place where I used to live. One day as I was sitting at the kitchen table, lightning struck the combination weather vane/lightning rod on the end of the barn right in full view about 150 ft. away. First of all when lightning strikes that close there is no waiting to hear the thunder as it is simultaneous with the strike. Real scarey! Anyway, there was a shower of sparks at the rod but when I went out to check the ground cable, it was as cool as a cucumber. This system had been installed in the 40s and everything used in the istallation was made of copper including the nails and straps and the grounding wire was real heavy gauge. I often wondered if lightning would have hit the barn if the rod had not been there?
I once worked on a prison farm here in NYS and one afternoon lightning struck a huge maple tree where we had two freshening cows pasturing. Of course they were under the tree to escape the rain. Both were killed instantaneously. The ends of the roots popped right out of the ground and the tree was split down the middle but it survived. We had our own slaughtering plant so we called a couple of the inmate butchers out and
butchered the cows so it was not a total loss.
Lightning is powerful stuff!

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two mile

04-05-2007 07:48:10




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 Re: O/T Question - What are the purpose of lightni in reply to Turke Bros. Farms, 04-05-2007 07:16:00  
I am confident that they serve a practical purpose that has a scientific explaination. Reguardless, they also have a decorative purpose. Ours have white glass balls that do absolutely nothing, and we have a wind vane attached to one of them with a leaded glass tail. When we reroofed our barn several years ago, we spent a lot of time looking for a vendor that could hot dip galvanize the support frames. They are part of the charactor of our barn, not unlike having a chrome radiator cap on a tractor.

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mjbrown

04-05-2007 07:38:27




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 Re: O/T Question - What are the purpose of lightni in reply to Turke Bros. Farms, 04-05-2007 07:16:00  
The purpose of lightning rods is to put the salesman's kid's through college.;-)



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KRUSS1

04-05-2007 09:46:13




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 Re: O/T Question - What are the purpose of lightni in reply to mjbrown, 04-05-2007 07:38:27  
And apparently to draw out a lot of very long winded answers.



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georgeky

04-05-2007 07:33:21




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 Re: O/T Question - What are the purpose of lightni in reply to Turke Bros. Farms, 04-05-2007 07:16:00  
It was alway's my understanding that they were intended to attract lightning. The rod is grounded by a copper wire to a ground rod drove in the ground. It is suppose to run any charge into the the ground instead of the building.



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Bob

04-05-2007 07:28:28




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 Re: O/T Question - What are the purpose of lightni in reply to Turke Bros. Farms, 04-05-2007 07:16:00  
The theory is that they "bleed off" electrical charges BEFORE a buildup leading to a "strike" occurs.



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dan hill

04-06-2007 02:43:23




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 Re: O/T Question - What are the purpose of lightni in reply to Bob, 04-05-2007 07:28:28  
Trees are struck often by lightning.A big red oak was struck and killed on the edge of my field.It had a split the entire length of the trunk when I cut it for fire wood.A 150 year old church had its steeple destroyed last year in Jan.No rods.A church in Palmyra had a strike on the steeple 5 years ago.Steeple was rebuilt and got struck last year, church burned down this time.No rods.This church was high above the road on a granite out cropping.Lightning strikes seem favor ledge areas.Chimneys are often targets.I answered a fire call where lightning struck a big maple , cut a furrow thru the grass and traveled thru a wire fence around the flower bed then on to the house telephone.The cellar was full of smoke and 2 light bulbs were blown out of their sockets.No fire was found but we kept the truck there for 2 hours just to be sure.A friend has been struck twice by lightning, once in an aluminum boat the second in his kitchen.My first house had a good sized pine beside it.Lightning struck the tree and jumped to the phone line in the cellar several times.A boy was struck and killed carrying a steel fish pole years ago.A nother boy was standing on a small porch during a thunder storm .Lightning struck a large maple,came along a wire dog run attached to the porch and killed the boy.I think the lightning would have gone to earth if the dog wire was grounded .I have had many close calls with lightning.I do think lightning rods work and wish my buildings had them.I cant remember a building that had rods on it being struck and burned.Lightning can strike at any month of the of the year...

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rrlund

04-05-2007 07:42:08




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 Re: O/T Question - What are the purpose of lightni in reply to Bob, 04-05-2007 07:28:28  
Yup,as I understand it,there are 2 halves to a lightening bolt. The one coming down and the one going up to attract it. It will go to the strongest charge from the ground. The rods are supposed to neutralize that charge.



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