ECN Forum Forums General Topics of the Trade General Discussion Area Lightning rod theory of operation?

GM, there are cloud to cloud strikes, and cloud to earth strikes. "Leaders" come from the clouds, and reach up from the earth to form a path.

From the site you posted:

"""The leader that reaches the earth first reaps the rewards of the journey by providing a conductive path between the cloud and the earth. This leader is not the lightning strike; it only maps out the course that the strike will follow. The strike is the sudden, massive, flow of electrical current moving from the cloud to the ground. """

If lightning orginated at the earth and went to the cloud, I would put lightning protection on my nieghbors house.


Dnk......

Here are some more interesting links.
http://www.arrl.org/tis/info/lightning.html

Radio hams on how to protect high antennae.

http://en.wikipedia.org/wiki/Talk:Lightning_rod

The wikipedia article is hedging its bets. It claims that there are TWO modes of operation: gradual discharge, to prevent (not to attract) lightning, AND conduction, in case of a direct strike.

Anyone figuring out how to control or attract lightning can name their price and retire. The utility companies have been trying to figure it out for decades.

Dave

I think the only thing that's agreeabble is that no-one can agree on this.

But we spend money to figure out why frogs don't fly...

Go figure.....


Dnk.....

Is there a difference between the average ground rod used at single family dwelling and a lightning rod?

I agree with marcspages.

If I recall, the problem with most lightning rod systems is that they are too small relative to the distances and currents involved.

It is hard for a 1000' lightning rod to equalize the electrical potential across 30,000'.

Shockme,
A residential ground rod is >8' long and is buried in the ground.
An air terminal is 12"-48" and is mounted in various areas of the roof extending into the air.
My point regarding the Physics teacher is that there are various theories, and none are a slam dunk. I generally teach several concepts, and suggest that they become a physisist when they grow up

The modern theory, propounded by Isaac Asimov, is that the true energy pump for these voltage differentials is cosmic radiation.

The earth is constantly bathed in such radiation. It energizes the upper atmosphere somewhate in the manner of a capacitor.

When the weather is appropriate the concentration of energized air molecules are ripe for a triggered release.

Some cosmic radiation is especially ionic and penetrating. It is assumed that they are the source of the 'leader' strike. Unlike current in a wire this charge carrier drives down through the atmosphere as if it were a cloud chamber at the end of some partical accelerator.

This functions much the same as if you were to drop some #16 across high voltage mains bussing -- hot to hot. The wire would explode into a plasma arc, which would then be sustained.

Unlike mains bussing, the pool of energized ions is comparatively small while the energy per electron is way, way high.

As the strikes proceed the earth operates as a conductor -- replacing the discharged ions. Florida, with its high water table makes for an ideal mobile electron tank. Hence it is no surprise that it holds the American records for repetative lightning strikes in an area.

Q. How does lightning form?
A. Lightning, a flow of electrical current between the earth and storm clouds, occurs as varying charges of positive and negative polarity build up in the atmosphere during a storm and begins to ionize the air. As more air is ionized and the result is a conductive path to earth. A discharge or current sent rushing toward the earth. As this downward force nears the earth's surface, positive charges rise up to meet it from many objects at earth level. As the negatively charged stepped leader thrusts toward the ground readying to discharge its energy, its path is erratic. Nearing the earth, positive charges are attracted by it and begin to arc upward from roof edges, lighting poles, antennas, etc. When any of these two opposing charge systems meet, they create a closed circuit. As the path to the ground is completed, a flash is created. This can occur several times as the cloud will recharg at a rapid rate.

Q. What happens when a building is struck by lightning?
A. A lightning strike to an unprotected building can be catastrophic. Packing up to 100 million volts of electricity and a force comparable to that of a small nuclear reactor, lightning has the power to rip through roofs, explode walls of brick and concrete and ignite deadly fires. In addition to structural damage, lightning surges throughout power lines causing wire damage and destruction of valuable electronic equipment including computers, televisions, stereos, security systems, etc.

Q. How does a certified lightning protection system work?
A. A lightning protection system provides a designated path for the lightning current to travel. The system neither attracts nor repels a lightning strike, but simply intercepts and guides the current harmlessly to ground.