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).]
If you asked four engineers, you would get five different opinions on this topic
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."
Scott " 35 " Thompson Just Say NO To Green Eggs And Ham!
#56700 - 09/28/0511:46 PMRe: Lightning rod theory of operation?
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.
#56702 - 09/29/0506:53 AMRe: Lightning rod theory of operation?
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
#56703 - 09/29/0507:05 AMRe: Lightning rod theory of operation?
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.
ps. Which could explain how he survived the crazy kite stunt.
[This message has been edited by Alan Belson (edited 09-29-2005).]
Wood work but can't!
#56704 - 09/29/0507:23 AMRe: Lightning rod theory of operation?