The special lightning rod

Hi All
Is there a lightning rod that doesn't absorb lightning?!
I mean ,I need a Rod that it doesn't let lightning strike to the protected area.

NO
You can only absorb lightening or reroute to ground.
The extreme high voltage looks for a short conductive route.
even if you put up a ceramic rod it will look for a better way or the dust rain combination on the rod.

That's the whole point of a lightning Rod. It's dissipates a charge before it exceeds the breakdown voltage of air!. It's not supposed to attract lightning.

Absolutely correct. The point on the end of the rod that points up towards the sky acts to dissipate the charge, preventing the voltage from getting high enough to cause lightening. That's the theory, at least. Not sure it it's 100%. Might help to erect several around the area you wish to protect.

From Wikipedia:
"A lightning rod (US, AUS) or lightning conductor (UK) is a metal rod or metallic object mounted on top of a building, electrically bonded using a wire or electrical conductor to interface with ground or "earth" through an electrode, engineered to protect the building in the event of lightning strike. If lightning hits the building it will preferentially strike the rod and be conducted to ground through the wire, instead of passing through the building, where it could start a fire or cause electrocution."
__________

Theoretically (that is, off the top of my head), to prevent a lightning strike in a particular place, it would be necessary to generate an electrical potential (approximately) equal to the thundercloud, because current does not flow between places of equal potential.

So I suppose, a _charged_ lightning _prevention_ rod at equal potential to the cloud (perhaps a hundred million volts or so) could discourage lightning strikes in its general area.

I hereby claim full patent rights for this invention. Please contact me for manufacturing licenses.

I'll be darned -- I guess I have that wrong. Here's another document that refutes my position:

* http://www.usfcam.usf.edu/cam/exhibitions/199..._McCollum/supplemental_didactics/21.Uman2.pdf

The reason I believed that a pointed rod would dissipate the charge that might produce a strike, is the fault of this guy [@7:43 minutes]:

* http://www.youtube.com/watch?v=ubZuSZYVBng&feature=share&list=PL2BF9B455E533AB7A

I don't know, looks plausible to me, based on his demonstration -- but maybe it doesn't scale up.

I notice:
The sparks between the domes are sudden discharges, so that the high voltage dome is repeatedly charging and suddenly discharging.
When the man points the nails at the HV dome, there is no visble spark, but the other discharge ceases.

Difference: the other dome is grounded, so when the spark occurs, the HV dome is suddenly discharged.
But when he points the nail, the current must flow through the resistance of his body, and the charge is being gradually dissipated.
(The current though the air then being too small to produce a visible spark.)
(A pointed nail tends to attract the charge better than the rounded dome.)

In both cases (I would guess), the same amount of charge is being dissipated over a period of time, i.e. the same AVERAGE curent is flowing.

His equipment may produce 200 kV, but its internal resistance must be so great that only a very tiny current can flow from the dome, so he is never in danger of electrocution.

Lightning clouds work at hundreds of millions of Volts, and have the capability of discharging tens of thousands of Amps (although only briefly).
If a lightning conductor could gradually dissipate the charge out of a thundercloud, it would be a quite useful source of power, even if only occasionally !

A very nice picture from the wiki page on corona discharge. I do believe at one point salesmen went door to door selling lightning rods to home owners 1930s-1940s. They would use a picture like this to convince people that the rod would bleed electricity from the air around their homes. While true that the point tends to have electrons crowded near the tip and thus becomes the jump off point for those electrons, as power levels increase and the threshold voltage is exceeded a spark forms. This will naturally occur at the tip of the rod as the ionized air has a lower resistance than normal air. So if there was a rod that was having a corona discharge, the ionized air would be rising into the atmosphere and could create a lower resistance path to ground for a lightning discharge. In practice the ionized air would probably be dissipated, there would generally be considerable wind when lightning is probably.

bq). Difference: the other dome is grounded, so when the spark occurs, the HV dome is suddenly discharged.
But when he points the nail, the current must flow through the resistance of his body, and the charge is being gradually dissipated.

Yes, I think you're right.

bq). (The current though the air then being too small to produce a visible spark.)
(A pointed nail tends to attract the charge better than the rounded dome.) In both cases (I would guess), the same amount of charge is being dissipated over a period of time, i.e. the same AVERAGE current is flowing.

Yes, I think it's that the point on the nail collects charge and concentrates it thus generating a large potential that ionizes the air and provides a current path. It is a much smaller current because there is less charge involved (only the amount of charge that collected on the point of the nail -- not the far greater charge than must accumulate on a flatter surface in order to ionize the same air path (granted a bit shorter, because the nail is closer to the charged globe, but in terms of a lightening rod, not that much difference in distance).

Because it's a much smaller current, it goes unnoticed. It would be an interesting experiment to monitor currents in a lightening rod during a storm.

bq).His equipment may produce 200 kV, but its internal resistance must be so great that only a very tiny current can flow from the dome, so he is never in danger of electrocution.

I don't think this has to do with internal resistance. I think it is merely the amount of charge that builds up before the air ionizes and provides a path for the charge to leak off. The currents in a thunder cloud discharge are so much higher, because there is so much more surface area for charge to accumulate. More charge means higher currents during discharge.

bq). If a lightning conductor could gradually dissipate the charge out of a thundercloud, it would be a quite useful source of power, even if only occasionally !

Yeah, I wonder if this is an untapped energy source? Might be a boon in places like Florida, Central Africa, and Singapore.

I did some more reading on how a lightning rod works and there are three camps:
1. Those that say it works merely by being the highest grounded conductor in the vicinity, thus the best path to ground..
2. That it's point effectively bleeds down the charge thus preventing the strike altogether.
3. That both effects are present and then the bleeding down of charge isn't always enough to prevent a strike, but when it happens, the rod is struck because of it's the best path to ground.

The problem with the idea of "charge being dissipated" by a rod is that the place the lightning charge is building up is within the cloud, a few miles above the rod. As far as I can make out (from minimal reading up on the subject), there is no charge in the air locally surrounding the rod.
It raises a point of ground potential above a building, and thus will attract lighning that would otherwise strike somewhere close by.

I understand really tall buildings get struck regularly, and therefore benefit the most from rods, as their electrical systems would otherwise present a particularly attractive ground point for lightning strikes.

An interesting story, "The Lightning-Rod Man" by Herman Melville.

http://www.melville.org/lrman.htm