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#56696 - 09/28/05 03:44 PM Lightning rod theory of operation?
Scalar Offline
Junior Member

Registered: 09/26/05
Posts: 1
Does anyone know what the official theory is for how lightning rods work? I've heard some different claims and I don't know which is correct.


Some people say that lightning rods help prevent lightning strikes by dissipating the voltage difference between the sky and the ground. Storm clouds mostly carry positive charges while the ground carries a negative charge.

The rods are pointed on the end specifically so that they act as electron emitters, though the emission is nowhere near rapid enough to generate a visible corona. The rods carry the negative potential up from the earth, spray it into the air, and help ionize the air and dissipate the charge-difference in the air that could lead to a lightning strike near the building.


And other people say that none of this happens. The rods are simply there to provide an easy route for the strike to follow, rather than along a path that leads right through the frame of the house, for example.

There is no dissipation or ion-streaming effect, and the rods don't need to be pointed at all... a cut-off flat or rounded stub is equally as effective.

Rods also don't do anything to reduce the frequency of strikes, and buildings with lightning rods are struck no more or less than structures without them.


So which of these is it? Is there any charge dissipation occurring, or is it only just an easy path to ground?



[This message has been edited by Scalar (edited 09-28-2005).]

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#56697 - 09/28/05 04:11 PM Re: Lightning rod theory of operation?
Jps1006 Offline
Member

Registered: 01/22/04
Posts: 609
Loc: Northern IL
wouldn't an ammeter confirm the flow of electrons? Is anyone brave enough to collect data both during good and bad weather? Where is Ben Franklin when you need him?

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#56698 - 09/28/05 05:36 PM Re: Lightning rod theory of operation?
Ron Offline
Member

Registered: 03/13/02
Posts: 577
Loc: White Plains, NY
If you asked four engineers, you would get five different opinions on this topic.
There is lots of opinions on the web.
_________________________
Ron

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#56699 - 09/28/05 08:06 PM Re: Lightning rod theory of operation?
Scott35 Offline

Broom Pusher and
Member

Registered: 10/19/00
Posts: 2679
Loc: Anaheim, CA. USA
 Quote:

If you asked four engineers, you would get five different opinions on this topic


LOL!!!

I am leaning towards "The Other People's" descriptions, from "Scalar"'s post, as being more accurate.
"Other People" description would be the one starting with:
"And other people say that none of this happens."


Scott35
_________________________
Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!

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#56700 - 09/28/05 08:46 PM Re: Lightning rod theory of operation?
Bob Offline
Member

Registered: 02/05/02
Posts: 182
Loc: Mobile, AL, USA
Do a google search and find out for your self. Ltg rods do not prevent a strike.

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#56701 - 09/29/05 03:42 AM Re: Lightning rod theory of operation?
George Corron Offline
Member

Registered: 05/16/01
Posts: 728
Loc: Lorton, Va USA
Lightning rods do not prevent a strike?

Okay... I disagree with that one. The most widely held theory is the equalization of charge between earth and sky. Now the debate begins as to whether the sky is pos or neg, or which is which, doesn't matter, it releaves the imbalance condition which causes a strike.

"Easy path for a strike to follow". Nah, we ain't got wire enough for this, too many amps for a pathway, well, more than once.

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#56702 - 09/29/05 03:53 AM Re: Lightning rod theory of operation?
Trumpy Offline

Member

Registered: 07/05/02
Posts: 8470
Loc: SI,New Zealand
Good on ya George!.
Common thought would have it that lightning strikes the ground.
To a degree that is untrue.
From the highest point in a given area, high speed photograghy will show you that there is a "leader" that goes from the ground up to make contact with the Cloud-Ground contact.
It is that contact that gives the sound of the lightning strike.
_________________________
Let's face it, these days if you're not young, you're old - Red Green grin

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#56703 - 09/29/05 04:05 AM Re: Lightning rod theory of operation?
Alan Belson Offline
Member

Registered: 03/23/05
Posts: 1800
Loc: Mayenne N. France
The whole point ( no pun intended) of a lightning rod is to leach away electrons in a controlled manner to ground to pre-empt a strike proper, as conditions move toward an event? As George points out ( no pun intended) we ain't got enough wire to carry a stroke safely down a building more than once. They aren't, as far as I'm aware, continually renewing the LC on the Empire State Building, which is said to get struck many times per year. The point is, ( NPI), Good Ol' Ben did all the experimental work some 12 score and ten years ago. And he found, by experiment, that a point on the rod ( his was made of iron- Yankee parsimony? ) seemed to give better results. He had some kind of bell mechanism rigged up in his stairwell to indicate that some kind of electric current was flowing during thundery conditions, and we know this worked because there is a letter extant from his wife to Ben in England begging him for directions as to dismantling the bloody thing as it was driving her to distraction.

Alan

ps. Which could explain how he survived the crazy kite stunt.

[This message has been edited by Alan Belson (edited 09-29-2005).]
_________________________
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#56704 - 09/29/05 04:23 AM Re: Lightning rod theory of operation?
Dnkldorf Offline
Member

Registered: 12/12/04
Posts: 1091
Loc: nowhere usa
I think the rods are "pointed", so you can pound them into the ground.

(How I got ground rods out of this, I'll never know)

We are discussing air terminals, right?

Lightning will hit anywhere it wants to, we can't "as of yet", control where it will hit.

Lightning rods, and lightning protection systems, do not "attract" lightning, they provide an easy path to earth, so the strike can be disapatted.

Roger Block has some interesting books on this. Alot goes into it, alot more than I had ever thought.


Dnk...

[This message has been edited by Dnkldorf (edited 09-29-2005).]

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#56705 - 09/29/05 09:50 AM Re: Lightning rod theory of operation?
John Crighton Offline
Member

Registered: 05/16/05
Posts: 172
Loc: Southern California
Lightning rods are pointed because the electrical charge is most dense at the point.

For the same reason, ultra-high-voltage terminals are spherical, so the charge is evenly distributed.

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