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B lightning striking electric circuits

  1. Jul 11, 2017 #1
    Why does lightning seem to hit objects with free electric currents inside (like computers or cell phones) more than "neutral" objects?
     
  2. jcsd
  3. Jul 11, 2017 #2

    davenn

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    computers and other house hold items ... TV's, DVD's freezers etc etc will get damaged because the lightning has hit the outside powerlines on the street
    which then conducts the high voltages into the house

    a cellphone WONT get struck unless it's plugged into the charger or if a person carrying the phone outside gets struck
     
  4. Jul 11, 2017 #3

    anorlunda

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    Neutral objects. Do you mean trees? Rocks? Dirt? It does hit them frequently.

    I thunk your question is like, "Why does toast always fall butter side down?"

    Edit: I forgot the EMP from nearby lightning strikes. Is that what you mean?
     
  5. Jul 11, 2017 #4
    I know lightning hits objects like trees but isn't it more likely to hit something with electric circuits running inside it?

    There was an incident where lightning struck through the glass and hit one of the computers here. So I'm wondering about that.
     
  6. Jul 11, 2017 #5

    davenn

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    NO that is incorrect and will only do so for the reasons I stated
     
  7. Jul 11, 2017 #6

    anorlunda

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    The thing I forgot in #3 was EMP.

    A boat 50 feet away from my boat was hit by lightning. Although I have no direct evidence of a direct hit on my boat, all my electronics (including hand held devices) were fried. The only explanation I could come up with was EMP, but a layman might easily say that the devices were "hit" by lightning.
     
  8. Jul 11, 2017 #7
    Oh okay wow... I didn't know lightning strikes could do that. I'm not very familiar with EMP. Does it propagate as a burst of photons or something else?
     
  9. Jul 11, 2017 #8

    anorlunda

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    In my case, it could have been current coming down the mast, to the thick cable that attaches to a "dynaplate"; an underwater metal plate for grounding purposes. But again, I have no direct evidence, only speculation.
     
  10. Jul 11, 2017 #9

    davenn

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    just plain old electromagnetic radiation .... Radio Frequency, light :smile:
     
  11. Jul 11, 2017 #10

    phinds

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    EMP means "electromatic pulse". A strong one causes large induced currents in electronics that blows them all to hell and gone.
     
  12. Jul 11, 2017 #11
    Lightning hits power lines very frequently because they are very high, just like trees.
     
  13. Jul 11, 2017 #12

    Drakkith

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    According to wikipedia, lightning definitely releases an EMP that can disable nearby electronic devices. See here: https://en.wikipedia.org/wiki/Lightning#Transient_currents_during_flash

    It makes sense, given that there is a huge current spike within 1-10 microseconds. The ionized plasma channel that conducts the lightning strike should radiate just like an antenna.

    All EM radiation is made up of photons. An EMP is a strong burst of EM radiation in the microwave to radio-wave areas of the spectrum. This radiation is absorbed by conductors, just like a radio signal is, and induces are large voltage and current spike in them. This spike can then damage any electronics attached to the conductor (which is often a power line). The EMP itself can probably damage isolated electronic devices not connected to a conductor, but in a much more limited area since these devices don't have nearly the surface area of a large conductor through which to absorb the energy of the radiation.

    Just look up the wikipedia article on EMP's for more information.
     
  14. Jul 11, 2017 #13

    Baluncore

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    So long as we are dependent on sensitive electronics, we will think we are being picked on by lightning.

    Knowing that must be very comforting, but a significant lightning strike current will not pass through that plate without first blasting away the seal where that plate meets the hull. Changing currents do not flow through conductors, they flow over surfaces, around the outer edge.

    External bronze or stainless steel chain-plates are the way to prevent sinking and protect electronics. They keep strikes to the rigging out of the electrical power system and so away from the electronics. It may well be your “common grounding” plate that got your electronics fried.

    Lightning sinks small boats by destroying underwater sensors. A sensor's connection cable guides the strike to the surface boundary of the hole in the hull. The wet seal or plastic between sensor and hull may then explode as steam is generated. That removes the sensor and so makes a hole in the hull. It matters little what the hull material is, the insulated sensor cables will provide the guide.

    Rigging and external chain plates will normally carry the strike current to remain outside the hull until about 30 cm above the salt water line, where it cuts the corner through the air, away from the hull to spread over, and later into the water surface. An insulated hull without chain plates may have a hole burned or punched in the hull slightly above the waterline. That is where the strike current crosses from conductors inside the hull to the sea surface.
     
  15. Jul 12, 2017 #14

    anorlunda

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    :woot: If you want to spark a lively discussion among boaters, mention anchoring. To stimulate EEs, mention lightning. I'm no exception. I can't resist jumping in with more opinions.
    1. I resist anyone making definitive statements about lightning effects or lightning protection. Given 10 repetitions of an experiment with identical circumstances, I expect 10 different results. I have some experience with rocket-triggered lightning experiments so I've seen documented evidence of the variability of current paths.
    2. Even among authorities and code-writing bodies, there is no unanimity about lightning protection advice.
    3. The "seal" that @Baluncore mentioned on my boat is a 1/2 inch bronze bolt, and the hull is 1 inch thick at that point. Even if the penetration hole was enlarged by a current, it would not leak because the external plate itself forms a waterproof bond with the hull.
    4. I heard at least one anecdote about a similar boat with the mast connected to an underwater grounding plate. It was hit, and the the connecting cable vaporized sending molten copper through the cabin; yet the hull remained intact.
    5. My boat does have external chain plates, so they could indeed be a current path.
    6. There is zero physical evidence of my boat being struck at all. Therefore, one possible scenario is that the EMP originated on the neighboring boat 50 feet away that was struck and damaged.
    7. The evidence I do have is two-fold. First: I was on board with 6 other people when hit. I heard a ZAP sound, and thought, "That's very bad." But I recall no flash or thunder. The others on board noticed nothing. If the ZAP came simultaneously with a clap of thunder, I don't think I would have heard it.
    8. Second: All the items destroyed (SSB radio with backstay antenna, wind instrument with masthead sensor, radar with external unit halfway up the mast well within the cone of protection, hand held VHF, hand held GPS) were located in the cabin close to each other (within a 1 meter diameter sphere.). The sphere was within 50 cm of one of the chain plates).
    9. Other electronics within the sphere were unaffected. VHF radio with masthead antenna. Pactor modem, LED lights. Digital watch. Depth & Speed instruments. GPS chartplotter. Electronic battery charge controller. AC inverter. Hand-held depth sounder.
    10. When I visualize an EMP originating on the other boat, the first approximation is an omnidirectional expanding wave. But there are multiple sources of non-uniformity plus reflections on the other boat, on my boat, or from the water surface that could lead to non-uniform concentrations of EMP energy.
    11. The only evidence that it was EMP rather than a direct strike is that hand-held devices were affected.
    So I repeat. There are so many variables and so many possibilities in an event like a lightning strike on a boat, that it is crazy for anyone to make definitive statements about what did happen or what might happen in the future. When you see a hole blown in the hull (or lightning craze tracks, or vaporized wires), you can safely say that some current went there, but you can't say much about where else the current or the EMP went.

    The only word I like to use regarding lightning strike effects is enigmatic.
     
  16. Jul 12, 2017 #15
    An example of EMP happened to me when I was walking cross London Bridge (London, England) with my umbrella up and lightning struck the next bridge, which was Tower Bridge. A spark jumped from the metal shaft of my umbrella to my hand, a distance of about an inch.
     
  17. Jul 12, 2017 #16
    Did you think I said 'protons?' =)
     
  18. Jul 12, 2017 #17

    davenn

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    nope ... why do you ask ?
     
  19. Jul 12, 2017 #18
    Yep lightning is bad for electronic stuff.
    Best to turn off computers and other non essential electronics if it's a serious lightning storm.
    Not joking, I have lost valuable stuff twice.
     
  20. Jul 12, 2017 #19
    Well, I said photons and you said no... aren't photons the same as electromagnetic radiation?
     
  21. Jul 12, 2017 #20

    phinds

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    You seem to think that photons are like little bullets. That's not what happens. It's an electromagnetic wave. When it HITS something, photons are the result of an interaction
     
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