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What happens if "hot" wire touches Earth ground?

  1. Feb 28, 2015 #1
    Greetings !New to the forums.
    Here expanding my concept of what AC Electricity is
    My question (correct me if wrong)..
    If AC power alternates between +,- at a rate of 60Hertz/second and negative is used as -earth- at the AC generator

    If the hot wire touches the ground would happen? (I think Nothing)

    Cause by the principle of my understanding if I touch a live "Hot" ac wire and I am standing still to the ground current from the "hot" wire will travel through me to reach the potencial difference cause there is no voltage in ground .

    But since the current is actually passing through my body I will get electrocuted.

    Question is if this happens would the voltage go back to neutral?
     
  2. jcsd
  3. Mar 1, 2015 #2

    jim hardy

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    I think you need to get straight in your mind the basic concepts of

    energy
    work
    power

    charge
    potential
    potential difference


    current

    and learn the units of each

    before you become totally confused.
     
  4. Mar 1, 2015 #3

    jim hardy

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    Current will return to the source from which it came.
    If enough of it it travels through you to get there, you will indeed be electrocuted.
    If earth also provides a path back to that source, current might go through earth too.
     
  5. Mar 1, 2015 #4

    Nugatory

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    That is not right. If the hot wire touches the ground, there will be a somewhat exciting spark (I have some melted screwdrivers to prove it) and a rush of current from the hot wire to the ground. If a circuit breaker or other protection device does not open, things will explode, melt, catch on fire. If you happen to be part of that path to ground, you will receive a dangerous, perhaps lethal, electrical shock.

    What you may be missing is that the earth at the AC generator is not negative, it is zero. In a North American 60Hz 120 system, the hot wire is alternating between negative -170 and +170 (120 volts is the RMS average - google for "root mean square electrical power" for more), so there is a voltage difference from ground, and hence current flow in one direction or the other throughout the cycle.
     
  6. Mar 1, 2015 #5

    jim hardy

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    a compilation of electrical explosions


     
    Last edited: Mar 1, 2015
  7. Mar 1, 2015 #6
    Thanks very much for the replies !
     
  8. Mar 1, 2015 #7

    berkeman

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    Yikes! Did you see the Fire Engine that pulled up to the burning substation around 2:44 in the video? They thought better of it and drove right on by. Not a thing in the world they could do until the power was turned off... :wideeyed:
     
  9. Mar 1, 2015 #8

    jim hardy

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    Indeed you don't put water on an electrical fire . The stream will conduct current right back to the fire hose and whoever's holding it.

    Country wisdom : never pee on an electric fence.
     
  10. Mar 2, 2015 #9

    dlgoff

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    Last edited: Jul 13, 2015
  11. Mar 2, 2015 #10

    DrClaude

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    City wisdom: never pee on the third rail :wink:
     
  12. Mar 2, 2015 #11

    jim hardy

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    Don - you taught me that nuance of term "Step Voltage".
    DrClaude - I married a NYC girl. She confirms your advice .

    Thanks, guys !

    old jim
     
  13. Mar 2, 2015 #12


    Hehe.
     
  14. Mar 2, 2015 #13

    jim hardy

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    We tried an insulator wash system that used the principle of breaking the stream into droplets separated by enough distance to prevent conduction..
    It worked okay the first couple of times...... wish i had a video of that 240KV flashover

    Thanks for the confirmation !
     
  15. Mar 2, 2015 #14
    I've heard of power line insulators washing systems where they use water spray under high pressures. Water is of low conductivity or even tap water.
    Sounds insane but...
     
  16. Mar 2, 2015 #15

    jim hardy

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    Very pure water is a good insulator. Some generator windings are water cooled.

    I've heard of success washing insulators on transmission lines. Our trial on a transformer didn't work out well.
     
  17. Mar 2, 2015 #16
    System was the same used for washing insulators on transmission lines? Maybe it was used in a wrong way...
     
  18. Mar 2, 2015 #17

    jim hardy

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    Maybe. It was one of the earliest offerings. I see it's still done a lot of places.
    Washing%20insulators%20affect%20ADSS%20cables.png

    On a high line like that there's nothing immediately below the insulator, so runoff falls and separates.

    I'd be doggone nervous around this:
    image26.jpg
    Our failure was on a transformer with vertical insulators like these.
     
  19. Mar 3, 2015 #18

    rollingstein

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    Why is it not possible to design the analog of an automated circuit breaker? A short like that, doesn't it have some signature? I suppose you cannot just detect the high current because there might be legitimate reasons for a high current too?

    Some of those shorts seem to last for ever. It'd be nice to have an automated system trip the feeders. Too many false alarms?
     
  20. Jul 13, 2015 #19

    dbc

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    k..... now im confused....

    taking what Nugatory said into account.... A/C transformers primary coil are a direct path from hot ( >4000V ) to ground/neutral (unless you are considering the reactance of the inductor coil).... so why dont A/C transformers in substations and on poles blow up when they are hooked up since there is no resistance? Is the coil's inductor's reactance actually acting as the resistance of the circuit thus preventing current from flowing at a substantial rate? And what happens when the secondary side is disconnected? Does the primary current continue flowing?
     
  21. Jul 13, 2015 #20

    rollingstein

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    @dbc

    How so? On a delta-star AC transformer (assume you mean step down) the neutral grounding is on the secondary not primary side.
     
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