It seems to be commonly believed that the lightning rod functions by attracting lightning to the rod where it travels down the heavy cable and discharges to ground, rather than hitting the house or barn and likely starting a fire. However, one book I read said that, while the rod will do this, the primary function of the lightning rod is to reduce the likelihood of a strike in the first place allowing the charge differential (from the house and surrounding area relative to the clouds) to bleed off into the air. To do this the rod must have a sharp point. This was brought out in a discussion of the discovery Leyden jars (a crude capacitor). It seems Ben Franklin was playing with a Leyden jar but could not get it to collect up a charge because he was using a pointed electrode. He then switched to a rounded electrode (as the original Leyden jar had) and found it easily collected a charge. Thus he discovered a principal that he then applied to invent lightning rods (I believe he was the inventor).

Curious to hear your comments on this. Maybe an electrical engineer out there can verify it.

 

There was a recent study that claimed that blunt-tipped lightning rods actually work better than the pointed ones. Found an article about it:

http://abcnews.go.com/sections/scien...lin000515.html

As far as the principles behind it, I'm not an electrical engineer and have no idea whatsoever - as long as they keep my barn from burning down, I'm happy.

I've heard it described both ways - that they keep the lightning from striking by allowing the charge to dissipate, and that they 'attract' the lightning and allow it a direct path to the ground.

Edited to add: I re-read the article, and it sounds like they're saying the blunt-tipped rods work better because they attract lightning and are more likely to be hit. But, if your goal is to dissipate the charge, I would think you'd want the ones *least* likely to be hit (or the sharp-tipped rods) - which goes along with what you said. Maybe which lightning rod works "best" depends on what they want (or expect) the lightning rod to do...

LK

 

Interesting article. I like the idea of a sharp rod that gets struck less often. The question is, what gets struck instead. If the sharpie really does bleed off charge and there are less strikes, then it sounds like the better rod, but if the chance increases of a strike hitting the house instead of the rod, then I'll take the blunt rod, though I suspect the sharp rod could extend a little higher to compensate. (Wonder if sky divers look out for these things --of course they are not supposed to land on houses and barns). I know, put a sharp rod on the house and barn and then out if the field have a pole with a blunt rod to attract any remaining strikes.

 

Long time ago, I attended a meteorological seminar, that explained that lightning did not actually strike from the sky, but rather came from the sky to meet an opposite charge emanating from the ground. Should this hypotheses be accurate, the concept of charges dissipating into air would be reasonable. I have observed that structures with the older type pointed lightning conductors do receive less strikes than similar structures without such a thing. ( I get this assumption from researching the maintenance records of a few thousand churches worldwide.)

Theo

 

Ok, you guys asked for it. A little lesson in electricity.


In any situation where "electricity" is said to flow, you will have the movement of the electron towards the positive and also a "hole flow" (place where there is no electron - a positive charge state) that moves towards the negative pole. Don’t believe me; try imagining a row of full buckets. Take a full one and use it to fill an empty one. Put the empty one back down at the start of the line of buckets. Now use the third bucket to fill the second. Put it back down. See, full buckets move to the left, empty ones move to the right.

0XXXXX >
X0XXXX >
XX0XXX >
XXX0XX >
XXXX0X >
XXXXX0 >


It is this potential that is dissipated or prevented from forming in the first place by a sharply pointed lightning rod. More rounded shapes allow charges to build until maximum saturation of the surface is reached. Remember, at higher voltages electricity travels around and over a conductor, not through it like with 110v ac in your house. That is why you can see lightning as it hits a tree and travels down the trunk to ground.

Anyway, one charge builds up in the clouds and the other on the ground. Tall objects bring the two charges closer together and so the ark takes place there first. IE Churches and barns.

Don’t get me started on what an "electron" really is....

Hope this helps.

 

So while you all are explaining this phenom, maybe you can tell me why they used to have glass '*****' or globes on those pointed spears?

Decoration? or did they shatter if it took a hit, serving as strike indiators?

Shoot, now I started thinking.........................

 

I support the theory.
If you think about it lightning could never travel down a ground cable of that size. It would burn up without a problem. I read an article once that if it did attract lightning the ground wire would be the size of a tree trunk.

Dan 03 Ranger EDGE 4x4

 

hmmmm i remeber back in electronics school that they claimed hole flow was incorrect although the principals still apply
everyone knows that lightning comes from the ground up!

 

One of my former meteorology professors explained to us that a stroke of lightning is no more than an inch in diameter. It's the flash given off by the atmosphere around it that makes it appear much larger and more powerful than it really is. A conductive cable running off your house may very well channel the electricity into the ground and save your house. I've seen it happen with my own eyes before.

 

the way i understood it, the lightning rod acts as an air charge stabilizer, removing the positive charge around the house by essentially ground the exterior of the house.

 

Well, that round lightning rod theory sounds interesting, but it goes against current common practices. Many of the tall communications and electrical supply towers are required to use certain nuts and bolts with round heads on them to lessen the chance of lightning strikes.
On another note, have ya'll seen that movie "Sweet Home Alabama"? There is a guy in there that goes to the beach and uses lightning rods to make crystal clear sand sculptures of the lightning as it strikes the ground. Bogus. Of the educational nature shows I've seen the results of the lightning strikes in the ground leaves ugly malformed hollow chunks of charred silica and rock. Nothing even as remotely nice looking as what's in that movie. That's Hollywood for ya.

 

I don't really know about lightning rods, specifically. I can tell you that a rain channel mounted CB antenna on a 1977 E250 Econoline Club Wagon works really well, that is if the lightning is supposed to hit the rod.

We were struck by lightning travelling down I-40 near Twin Arrows, Arizona, and actually at Buffalo Range Road in 1983. It fried the control module and the cruise control and the inline fuse to the CB. It melted the back doors shut, and left zigzag burn holes down the roof of the van.

Anyhow, I like all the theories and never thought about it before. I always thought that lightning was supposed to hit the rod, not the house because the rod provided a shorter path to ground. Interesting thoughts and information.

By the way, there is no sound in lightning. All we saw was a blinding flash(several times more intense than a camera flash). No pop, nothing.

 

Wow! I think I will sharpen my radio antenna to a point to bleed off the static charge from my pickup truck hoping that way I won't get struck

 

Check out this link if interested in more info on preventing and disapating lightning strikes.

Before I followed this guys advice, we would loose a pole transformer and lots of electronic things about once a year. For last four years have watched many neat storms NOT hit us.

http://home.attbi.com/~k9sth/Lightning_Primer_1.htm

 

Hey you know that tiny bead on the end of the antenna is not so you don't poke your eye out, it's called a static ball to reduce static on your radio. Any RF engineers here to explain how that works?

Barry