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lightning rod question

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

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  1. rayjking

    rayjking Guest

    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. 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.")


    Still reading?

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

    Tom
     
  5. Tom Biasi

    Tom Biasi Guest

    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
    answer.
    There are still things much greater than ourselves to discuss however.
    Best Regards,
    Tom
     
  6. Rich Grise

    Rich Grise Guest

    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. 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 Myers

    Bob Myers Guest

    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 Wormley

    Sam Wormley Guest

    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 Kelly

    Don Kelly Guest

    -----------
    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. 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 Grise

    Rich Grise Guest

    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 Grise

    Rich Grise Guest

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

    Ba-dump-bump!
    Tsssssh!
    Rich
     

  14. 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. 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 Myers

    Bob Myers Guest

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

    Bob M.
     
  17. Tom Biasi

    Tom Biasi Guest

    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 Grise

    Rich Grise Guest

    Firesign Theater, "Everything You Know is Wrong".

    Cheers!
    Rich
     
  19. 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. "I have heard...somehow"

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