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Ground fault- Why doesn't anyone get shocked?

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  • mbrooke
    replied
    Originally posted by romex jockey View Post
    Earth's R factor.....~RJ~


    Seems to play a role here.

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  • romex jockey
    replied
    Earth's R factor.....~RJ~

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  • mbrooke
    replied
    Originally posted by romex jockey View Post
    Maybe i was channeling Mr Kirchhoff again......~RJ~
    What do you have in mind?

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  • romex jockey
    replied
    Maybe i was channeling Mr Kirchhoff again......~RJ~

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  • mbrooke
    replied
    Originally posted by romex jockey View Post
    Looks like some of these 'earthing systems' make a difference Mr. mbrooke .....~RJ~
    Appears that they do

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  • romex jockey
    replied
    Looks like some of these 'earthing systems' make a difference Mr. mbrooke .....~RJ~

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  • mbrooke
    replied
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  • mbrooke
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    [COLOR=#ffffff]iii[/COLOR]
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  • mbrooke
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    [COLOR=#ffffff]ooo[/COLOR]
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  • mbrooke
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    [COLOR=#ffffff]vvv[/COLOR]
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  • mbrooke
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    [COLOR=#ffffff]...[/COLOR]
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  • mbrooke
    replied
    Originally posted by mivey View Post
    LV GFCI and MV are not the same application of course.


    The NESC does say that the primary and secondary neutral should be connected when you have a MGN system.
    Food for thought. What do you think? Is this a legit way of determining if they should be interconnected?
    Attached Files

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  • mbrooke
    replied
    Originally posted by mivey View Post
    LV GFCI and MV are not the same application of course.
    True- but the physiological response to any given shock does not change.


    The NESC does say that the primary and secondary neutral should be connected when you have a MGN system.

    True- but nothing on how to limit the duration of the voltage imposed on the LV neutral.

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  • mivey
    replied
    Originally posted by mbrooke View Post
    But the graph is:
    ...
    UL felt it good enough to be taken seriously here using it as a foundation on which industrial GFCI protection is implemented.
    LV GFCI and MV are not the same application of course.

    Originally posted by mbrooke View Post
    But I am theorizing that in some cases it does more harm then good.

    2.4kv can be brought into the structure.

    There is nothing in the NESC which says this voltage must be cleared under 5 cycles.


    I'd like my theory challenged and discussed because its something I'm genuinely curious about.
    The NESC does say that the primary and secondary neutral should be connected when you have a MGN system.

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  • Wayne Eckert
    replied
    MGN

    Originally posted by mbrooke View Post
    Ok, say you have a 7,200 volt single phase line running down your street. A a tree falls on the primary and it comes down on the neutral conductor.


    According to electrical theory 3,600 volts will drop across the phase conductor and 3,600 volts across the neutral going back to the substation.


    My question is, why doesn't 3,600 volts appear on the service neutral and thus everything in the home thats grounded?
    Simple answer is utilities, excepting California and a few others, utilize multi grounded neutral (MGN), which under the NESC requires the utility neutral to be grounded a set number of grounds per mile of neutral.

    Then the NEC requires the structures neutral to be bonded to the structures grounding system, so in the worst case, if everything is properly grounded and bonded during a cross fault, everything rises to the same voltage level with little difference in potential, therefore making it safe and minimizing damage and hopefully pulling enough amperage to either blow a lateral cutout, or run a recloser through it's cycles and until it locks out.

    Now that's the simple answer, in the real world there are many variables, some of which can burn a home to the ground or kill someone.

    But luckily between the NEC and the NESC the risk is greatly minimized.

    Wayne

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