# lightning rod question

Discussion in 'Electronic Basics' started by izzi4, Oct 19, 2004.

1. ### rayjkingGuest

I agree with the #8 wire not seeming to be adequate. The coast guard /
power squadron use the #8 wire and 60 degree protection cone as there rules
but for my sail boat I use a welding cable size ? connected from the
aluminum mast directly( no curves ) to the lead keel. I have observed a boat
being directly hit by lighting about 100 feet away from me. The vhf antenna
made a baby carriage size puff of orange smoke. No one was injured but the
electronics were fried.
I would like some explanation of ball lighting. I have known of a ball (
corona ) in the cockpit of a sail boat.

Ray

2. ### William J. BeatyGuest

Not true.

Even some reference books claim the above. They've fallen for
a type of physics myth; a "science urban legend."

Yes, in 1790 they assumed that a little bitty lightning rod could
discharge a miles-wide thunderstorm across the miles of space above
the rod. The experts reasoned that, after all, a needle could
discharge the main terminal of an electrostatic generator even
if the needle was many inches away. Researchers later figured out
how silly this was.

Check out Dr. Martin Uman's book "LIGHTNING" for some ACCURATE
lightning-rod discussion. (It's probably unwise to listen to
any of the emotional and dishonest "belief systems" espoused in
this thread, including my own! Go see what lightning physicists
actually say. Experiments and mathematical reasoning will win
over politics and "beliefs.")

Well then it's your own fault.

Why can't a lightning rod discharge the storm? The scale is wrong.
While a needle can discharge an electrostatic generator via ion-leakage
across a large gap, a lightning rod is not like a needle. A lightning
rod is tiny: like one fiber in a piece of felt if we obey the scaling.
If one fiber is slightly taller than the others, well, the high voltage
electrode doesn't care. If you erect a lightning rod, the storm
won't even notice.

Also, the scale is wrong for "charged wind" to transport any charge
upwards. If you hold a needle near a high voltage terminal, the
needle "emits" charged wind which travels at many cm per second,
and there is a significant electric current in the air; on the order
of microamps or tens of microamps. This easily shorts out an
electrostatic generator.

But if we scale things up and use a lightning rod and thunderstorm,
the "charged wind" coming from the tip of the rod STILL TRAVELS AT
CM/SEC SPEEDS AND THE CURRENT IS STILL MICROAMPS. To have a significant
effect on the charged storm cloud, this velocity would have to scale up
too. The lightning rod would have to "emit" an electric wind that
traveled at tens or hundreds of KM per hour, and the electric current
would have to be thousands of times higher than 10uA.

Note that the above is one of several "lightning rod controversies."
Emotions run high in such controversies, so you cannot trust what
either side tells you. You can't even trust many reference books!

3. ### William J. BeatyGuest

Interesting. I've also found that the "draining myth" has spread
to chindren's science textbooks.
What did he think would happen if such a small wire supported such
currents?

I've seen kiloampere (kilojoule) pulses applied to 12 gauge wire.
It doesn't vaporise. Instead it gets warm. So the issue is: if
lightning was guided by, say, some 10-gauge solid copper wire,
would the wire become hot enough to start a fire? I would have
to be VERY hot: think of how hard it is to start a fire using a
piece of wood and a soldering iron.

If the wire is bent into tight curves, the mechanical (magnetic) forces
of kilo-amp currents can break the wire. But this would have little effect
on its function: the high voltage arc could easily jump across any break.

True. They want to guarantee that the wires never become so hot that
they could conceivably start a fire.

On the other hand, it sounds to me like he first made up his mind, and
then he started looking ONLY for arguments that supported his viewpoint.
That's "religious style" thinking. Did he present the opposing arguments?

It's much better to start out not knowing, and then to collect lots of
arguments and facts both pro and con.

4. ### Tom MacIntyreGuest

And I just thought of a whole new meaning for the term "ball and
chain".

Tom

5. ### Tom BiasiGuest

I will always read what you have to say William.
I kind of thought that what I said may cause a "storm".
I recall having correspondence with Mark Kinsler when he began his research
in 1996 or so.
He often said then and it still seems true now that there is no clear
There are still things much greater than ourselves to discuss however.
Best Regards,
Tom

6. ### Rich GriseGuest

Would that be St. Elmo's Fire?

Ball lighning, like flying saucers, is/are willess spirits trying to
manifest without body, which doesn't work, much to their chagrin. ;-)

It would be kind of interesting to see if it's possible to come up
with something that could catch a ball lightning ball, so we could
study it.

Cheers!
Rich

7. ### Roger JohanssonGuest

St. Elmo's Fire is some kind of algea which glow in the dark, with the
same chemical processes as in fireflies. AFAIK

I have heard that ball lightning consists of superheated air, ionized or
plasma or something like that. The lightning has superheated the air and
some charge can maybe linger in the ball lightning. It is like water
droplets on a hot plate. They are isolated towards the hot plate by a
layer of steam. That is why the water droplets can survive so long.

In a dry climate the superheated air, or plasma, can stay together
because the air works as an isolator, somehow.

8. ### Bob MyersGuest

No, I'm afraid you're confusing your phenomena. St.
Elmo's is definitely the visible result of an electrical
discharge; see

http://www.fact-index.com/s/st/st__elmo_s_fire.html

Bob M.

9. ### Sam WormleyGuest

St. Elmo's fire is a plasma (i.e. a hot, ionized gas) that forms arounds
the tips of raised, pointed conductors during thunderstorms. It is known
as a corona discharge or point discharge to physicists.

10. ### Don KellyGuest

-----------
The use of a #8 conductor is a bit iffy- even for home use. In addition the
placing of a rod at each end of a gable roof is also very iffy. Even in the
old days, a cone of protection was assumed. 30 degree cone good, 45 -not
bad. The problem is that this left most of the roof unprotected by the rod
system. Fortunately the probability of any house sized area being hit is
pretty low.
Another thing that was once written into codes was the use of odd sizes of
conductors- e.g.#5- only available through the purveyors if lightning rods.
However, from all that I have read on the subject and some design work on
the basis of known principles (i.e. Moussa's work and EPRI).
Look at your instructor's contention: say #8 was used - about 0.0006
ohms/ft- lets make it 0.01 ohms/ft to allow for skin effect and whatever.
Now consider a typical stroke- about 35kA peak- Assume that it peaks in
about 1 .5 microseconds and lasts for 100 microseconds for an average
current of less than 20kA for 100 microseconds. Average power =4x10^6
watts--WOW! but energy per foot of conductor is 400 Joules. Not all that
great. The point of the rod may be gone but the rest should be OK. What
might happen is that there is a poor contact somewhere and a high energy
dissipation at that contact- blowing it to ratshit.

As r w_tom indicated grounding and the soundness of connections is
important. Thank you, w_Tom
No point in diverting 35kA into a 10 ohm rod where the down conductor is 2
feet away from your backside on the john. EM theory comes in to play more
when the stroke has occured- but little more than consideration of
travelling waves and their reflections need be considered from a protection
point of view. . The effect of a reflection can seriously burn your butt.

11. ### Roger JohanssonGuest

Okay, I must have confused it with another phenomenon. I thought about
something glowing in the water, on the water surface, seen especially when
waves break or the water flows around the bow of a boat, which is
explained as some kind of light emitting algea in tropical waters.

St. Elmo's Fire is obviously, from the examples in that link, an
atmospheric phenomena, similar to ball lightning.
The ball lightning explanation, in the link from the above url, is very
similar to my explanation though.

Not a good and complete explanation, but that is approximately what we
know today.

12. ### Rich GriseGuest

Naturally, I'll pounce on this one.

But, let's cut to the quick. People have been "discussing" this sort of
thing since people have been discussing.

There's a new question, howsomever.

And that question is:

What does it _feel_ like to live in the physical plane?

Thanks,
Rich

13. ### Rich GriseGuest

"Um, general? I think you've got your phenomena scrambled."

Ba-dump-bump!
Tsssssh!
Rich

14. ### Roger JohanssonGuest

I found a nice old picture of st. elmo's fire on a ship:

http://www.wordiq.com/definition/St._Elmo's_Fire

The picture makes it very clear that it is a massive discharge from
extended parts of an object, like the mast tops of a sailing ship.

15. ### Myxococcus xanthusGuest

That's focusing on the cloud-discharging capabilities of -one- rod,
obviously miniscule.

Would be the -combined- effect of (1) thousands of lightning rods in a
moderate-sized community, plus (2) hundreds of miles of transmission
line, telephone line, supporting cable, etc. suspended between
hundreds of tall poles and tall towers, plus (3) tall lamp posts, tall
antennas, etc. have a significant cloud discharging effect?

Order-of-magnitude estimate on this? I'm wondering, since I've seen
several ground/tree strikes while out in rural areas, but only one
direct strike to a tree in the city, and I'm an urban dweller.

Myxococcus xanthus

16. ### Bob MyersGuest

OK, Rich, that at least SOUNDS like a quote I should
recognize - is it, and if so, from where?

Bob M.

17. ### Tom BiasiGuest

I think maybe the actual quote was:
"Well, if I may respectfully submit, sir, I think you've got your phenomena
scrambled, General."

18. ### Rich GriseGuest

Firesign Theater, "Everything You Know is Wrong".

Cheers!
Rich

19. ### John PopelishGuest

What about the sharp points on the edges of millions of tree leaves?
At the magnitude of currents involved in corona discharge (not
strikes) the resistance of copper and trees is insignificantly
different.

20. ### Richard HenryGuest

"I have heard...somehow"

That's what I like. Clear, concise references.