Re: O/T Question - What are the purpose of lightni

Posted by Gary Schafer on April 05, 2007 at 08:58:23 from (75.74.131.91):

In Reply to: O/T Question - What are the purpose of lightning r posted by Turke Bros. Farms on April 05, 2007 at 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

Replies:

• Re: O/T Question - What are the purpose of lightni KEB 20:12:37 04/05/07 (0)

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