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

Many new lightning rods are not pointed for safety reasons. Look here . Research shows no loss of effectiveness.
Don

Well, I'll go to the foot of our stairs! How can you fall onto a lightning conductor point and injure yourself??!!!
Absolute bull***t!

Alan

I always told that you needed to put in several air terminals and wires around the building. In effect you were trying to build a "Faraday Cage" around you so that the lightning would go around the building instead of going through it.

Harold

From someone who was brave (read "mad") enough to connect equipment to lightning rods with the purpose of studying the magnitudes and durations of strikes.

Lightning (Franklin) rods do attract lightning if within the step distance of the strike - if outside then the strike may well miss the tip of the rod.

Rods don't increase the frequency of strikes for an area, but most certainly increase the concentration towards the rods within an area.

Some charge dissipation does occur (and I have seen the corona off the tip of a rod), but not enough to prevent strikes (come on, it's just travelled a few thousand feet. ya really think a few feet of ion cloud is gonna make any difference?).

Conductors can be made beefy enough to withstand a full strike.

Clouds can be both negative (general) and positive (about 1 out of 10 average) with respect to Earth.

Points are better, spheres will have lower attraction ratios.

M.

Alan I have been on plenty of flat roofed commercial buildings that it would be simple to trip and fall onto the points.

At one large building we where adding an addition to the GCs safety people would cover all the rods in the morning and then uncover them over night.

I specify the blunt tip air terminals now a days. I read an interesting study that concluded similar results between blunt tip and pointy.
I've have problems on roof mounted cooling tower equipment (or many commercial roof parapets) when pointy terminals are used, because it always would catch my shirt when I walked by.

Iwire, Ron,
Yes, I buy those arguments in favor of a blunt tip in such locations as commercial premises flat roofing for safety. I was thinking of the traditional 'church spire' arrangement. Browsing the Net just now I came across some references to Mars. It's so dry that static charges are believed to be going to be a serious problem for manned landings. Terming this effect "lightning in reverse", NASA engineers have developed a multi-tined "reverse lightning" rod to fit to Rovers etc.. It consists of many very fine titanium wires arranged aerial-wise to dissipate charges into the thin martian atmosphere, (in effect turning the atmosphere locally into "Ground"), to protect astronauts and electronic kit from discharges. Significantly, the thin titanium wires are sharpened to a very fine point.

Alan

Well I went out and searched around about lightning rods and there are a lot of theories, not many of them agreeing with my physics teachers' explanation. But I did find one that seems to meet what I see as the right reason. And whoever said it was right, lightning comes up from the ground and not down from the clouds. A lightning rod is more for providing a safe path to the ground in which nothing will overheat rather then to prevent them. Try this. http://science.howstuffworks.com/lightning9.htm
M@T

GMIntern,
What does your Physics teacher say? I don't get to electricity until Chapter 16, and I'm just now teaching Chapter 4. So I want to know what to say in front of the class, as everything that I read is conflicting. So I present it to the students that way too!

Well Ron, the last time I went over that was in my physics class last year, and I dont remember everything. But here is everything I can recall. Lightning is obviously electriciy, Ben Franklin figured that one out for us a long time ago, maybe back when some of you guys were kids, haha, just kidding. But he figured out, quite dangerously I might add, that lightning is indeed something like a visible path of electrons from the ground to the sky. Most people think that it is something that comes from the clouds, but actually it isnt. Lightning comes up from the ground to the sky. Now here is where it starts to get a little fuzzy. From what I can remember, there is electrical charge in the clouds, which will create lightning between clouds, but the real force behind lightning striking the ground is because the clouds and earth have a different charge. The main reason that the lightning will move from the clouds to the ground is due to ionization of the air in between. Ionization isnt the loss of electrons or protons, but simply these same electrons moving farther away from each other, sort of like a Van de Graaf Generator. Now dont take my word on all of this, I am after all human and subject to mistakes. I will recommend http://science.howstuffworks.com/lightning.htm for this one. Experts in a field can usually tell you more about it then a student can. Hope it helps. And my advice for teaching is to make sure you know what you are saying first. Because unless you are really good at bsing your way through something, you need to know what you are talking about before you can talk about it. Everyone usually likes the teachers who teach them things.
M@T