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Lightning travels through the path of least resistance

  1. Oct 6, 2005 #1

    I have a question for you, what I need to know is if lightning travels through the path of least resistance or the shortest path available. Hence would lightning travel through a 50Ft. piece of copper wiring or a 40 Piece of thick mj-11 coax cable. This applies in the design and engineering of a lightning rod mechanism for protecting antanae and satilite equipment.

    Thank You

  2. jcsd
  3. Oct 6, 2005 #2


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    I should think that it's the path of least resistance, but lightning is a far from simple phenomenon. There's a good article about it in a Scientific American magazine from a few months ago. I'm afraid that I can't remember exactly which one. It might be of some help. There are also some discussions about it here in PF, but once again my memory fails. Try using the 'search' tool to dig them up.
  4. Oct 6, 2005 #3


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    I am no expert in lightning either but if the two paths described above are in parallel then I would think that some fraction of the charge delivered by the strike travels in both paths (like in a current divider).
  5. Oct 6, 2005 #4


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    Lightning can behave very strangely. Lightning doesn't seem to like to turn corners. Consider a length of cable stretched out and suspended and it suddenly makes a sharp bend. When lightning strikes the cable it will arc off of it to ground as opposed to turning the corner and arcing to ground at what is a shorter distance through the air. Lightning contains VERY high frequencies and the inductance that the sharp corner creates is enough to do what I described. I have a friend who worked in a TV repair shop. Someone brought him a phone/answering machine that was hit by lightning. He said the cord on it was melted every one quarter to half inch. This was most likely caused by a very high standing wave ratio on the phone cord. The melted spots represent the peaks in current at 1 wavelength intervals. For those of you who are confused about Standing Wave Ratios and such do a little research on your own. When a transmission line has an SWR the current and voltage in different spots along its length are not the same.
  6. Oct 6, 2005 #5
    Lightning tends to follows what's called a trailer, A trailer is a difference in charge between the Earth and Cloud and is ralated to a stream of Ions that help make the connection before a strike occures, This is why they say, when you feel your hair stand on end it's because an Ion trailer is eminating from your body to created a short cut for the strike to occure, If you feel your hair stand on end then take immediate safety precautions according to that type of emergengy, The Ion trail is basically taking the most conductive path through the Air to allow for the strike, The Ion trail is invisible to the naked eye and only the up stroke or down stroke can be seen, The direction of the Ion trailer is dependent on whether the cloud has more charge or the ground has more charge and the least path of variable resistance, This will determine the type of strike that will occure.

    If it is night time and enough condensation is in the area of the trailer then saint elmos may be seen on conductive edges or corners, but the conditions for saint elmos has to be right.

    The amount of charge difference in your lightning rod will also determine the path the trailer will most likely take in accourdance to the charge in the cloud, There are many variables when dealing with this amount of voltage, especially since at these high voltages lightning will also follow an electromagnetic line of force like it was a wire.

    It would probably be good to read some good liturature on the subject since lightning at those voltages can sometimes be unpredictable to a point.

    If there are more than one trailers then the lightning will most likely take all the trailers to dissipate all its charge faster. This is called branched lightning.

    I play around with my 50,000v Fly back transformer and It can follow EM lines of force with a spiraling effect or cork screw effect.

    To have better protection from your lightning rod, Its a good idea to place a steel pole/Pipe at least 3 inches in diameter OD (Minimal) and 8 foot long put in a hole 9 feet deep, This makes a really good Primary Ground Rod that can be ground tapped, Using 1 or 2 Guage Solid ground wire is good, but Battery Cable wire is even better, it can handle more Amps and voltage than regular Grounding wire and the thicker guage is more efficient at making sure the strike goes to the ground.

    The deeper the Primary Ground rod is the more conductive the soil.Earth, If your ground rod is not deep enough then any dry spell in the weather can cause the ground to loose conductivity, Placing the Primary Rod in the ground 9 feet deep ensures that the Ground will always be efficiently conductive year around.

    If its not deep enough the lightning rod may be uneffective.

    Also apply weather protection to all of your exposed Copper ends to ensure there is no corrosion which can also cause a ground connection to be ineffective, Scotch Gard (Liquid Wire Lock) is good and can be applied by a brush or dipped.

    I hope this helps. :smile:
    Last edited: Oct 6, 2005
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