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Transient currents and effects

  1. May 20, 2014 #1
    Hello,
    My question is out of curiosity and pertains to transient currents and their possible effects on any electrical equipment. For example, The various electrical components(infotainment systems, headlights, radio etc) in a car are “grounded” on the chassis, If a live wire from a electricity pole carrying high current were to fall on my car, what effect would it have on the components in the car? would the high current cause damage to the components? what path will the current take? and is there a possibility for the high current to reach the component through its ‘grounded’ terminal?
    Could someone please clarify/explain the outcomes?
    Thank you.
     
  2. jcsd
  3. May 20, 2014 #2

    psparky

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    First of all, the rubber tires on your car are highly insulated. It will take a lot of voltage to penetrate them.

    Secondly, the electrical line lying on your car isn't interested in the 12 volt system on board, however, it is interested in returning to its nearest transformer.

    Thirdly, if there is enough voltage to penetrate the tires, the high voltage will enter the chassis, then go thru the control arm or axle, then thru the rim, then thru the tire, go thru the ground, back to its transformer. If there is enough amps as you put it, then the heat from this transfer will likely burn the electrical circuitry in the car along its path.
     
  4. May 20, 2014 #3
    Electrons oppose each other and want to spread out as much as possible in the given conductor. In this case, your car. Virtually all of the current will be traveling on the outside of your car, essentially acting like a Coulomb Sphere.
     
  5. May 20, 2014 #4

    psparky

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    I agree. It would spread out to the 4 tires evenly as you say. Then, since the car body is attached to the frame, it would then get onto the axles, rims, then tires. Or, if the voltage is high enough, it my bypass the tires and jump the air gap of a lower hanging wire on the car. Whichever resistance path is lower, its gonna take that one.

    If a person were sitting inside the car, the person would not get shocked. Again, the voltage wants to get back to its transformer, it's not interested in the person in the car. However, if the voltage is high enough, the person will get burned just like the surrounding electronics.

    Now if that person decides to get out of the car, that's another story. If the person steps one foot out while touching the car.....whammo! That person is now the ground and is now dead. This is often the case when an excavator digs up a high voltage wire......the guy sitting on the machine now has a decision in front of him....a life and death decision. And there are no tires on an excavator, only steel tracks so this baby is "red hot" in a high voltage situation.

    If the person were to jump out of the car, in that situation the person should be able to escape unharmed. You do have to be careful walking away tho. Smaller steps not lifting your feet would be better than larger steps. If high voltage is near by, your big step makes you a resistance, possibly causing you to be electrocuted.
     
    Last edited: May 20, 2014
  6. May 20, 2014 #5
    Thank you Psparky and MrSparkle for having taken the time to reply. I also agree with the person sitting inside the car not being harmed due to the creation of Faraday cage.
    "If there is enough amps as you put it, then the heat from this transfer will likely burn the electrical circuitry in the car along its path". (-psparky)
    Then Is there a possibility for this to happen say if lightning struck the car? Will the electrical circuitry of my car be destroyed then?
     
  7. May 20, 2014 #6
    none of the electronics are likely to be in the path of the lightning. The electrons connect with the outside of the car and stay outword while they make their way to the axle and then the tires. The chassis is certainly going to have lower impedence than anything leading to the stereo. Even if it struck a whip antennae, it would still want to spread out along the outside. Maybe the headlights could be damaged. Its hard to say for sure. I would say the biggest threat to the electronics would be the induced EMF from the lightning, not the lightning itself.
     
  8. May 21, 2014 #7

    psparky

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    article-0-154A8D98000005DC-174_634x417.jpg


    article-0-154A8D94000005DC-264_634x417.jpg

    Here's a picture of lightning striking a car.

    The guy inside was unharmed.

    The car just needed to be buffed out.....lol.
     
    Last edited: May 21, 2014
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