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Energy network Earthing

  1. May 10, 2015 #1
    Hi All,

    First post of many on the forum.
    On the Subject of earthing I had always been led to believe that electricity would always go to ground (if of course ground was the lower potential)
    I was talking to someone the other day who was discussing un-earthed transmission systems and live working on such systems. They seemed to infer that there was no danger of becoming part of the current path when acting as a route to earth from a live conductor to ground of an un-earthed system.
    Is this possible?
    Any insight would be greatly appreciated
     
  2. jcsd
  3. May 10, 2015 #2
    For current to flow there needs to be a loop. If you tough either side of an isolated secondary transformer and earth ground, there's no return path.

    However there could be a ground fault in which case you get zapped. There could be capacitive coupling between circuit and earth ground, forming a weak return path.
     
  4. May 10, 2015 #3

    jim hardy

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    we answer this question a lot.

    here's a quote from one of them
    https://www.physicsforums.com/threa...ound-rather-than-negative-pole.798525/#post-1
    and another from https://www.physicsforums.com/threads/how-do-you-ground-a-current-in-a-circuit.757305/#post-1
    check these threads
    https://www.physicsforums.com/threads/why-do-we-ground-an-electronic-circuit.810961/#post-1
    https://www.physicsforums.com/threads/why-ground-split-phase-residential.767111/#post-1
    https://www.physicsforums.com/threads/not-fully-understanding-grounds.622107/#post-1

    and come back with questions on anything that's unclear ?.
     
  5. May 10, 2015 #4

    jim hardy

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    With how powerful a microscope do you want to examine that question ?

    If there's absolutely no circuit from that power system to earth besides you, then no current can flow through you.
    He'd be right.

    All circuits have area, so does earth, so there is some capacitance between that power system and earth.
    That capacitance can complete a circuit and allow current to flow through you.
    He's not mentioned that.
    So long as that capacitance limits current to less than your can feel (a few microamps) it won't shock you.
    Your doorbell is a small enough power system system it won't shock you. Not enough capacitance.
    But a mid-size industrial system might push a goodly fraction of an amp through its capacitance and that's plenty to be lethal.

    That's one of the reasons we earth power systems and equip them with "ground detectors".
    Check out "IEEE GREEN BOOK" for a really thorough lesson.
     
  6. Jul 26, 2015 #5
    Sorry for the late reply, but thanks for all the replies much appreciated, although maybe created more questions, thanks all
     
  7. Jul 26, 2015 #6
    Its quite safe to work on live conductors as long as you are at the same potential as the conductor and inuslated from any other potential.

    This is how linesman are able to work on EHV lines.


    The term Earth is defined in British law:
    http://www.legislation.gov.uk/uksi/1989/635/regulation/8/made
    "A conductor shall be regarded as earthed when it is connected to the general mass of earth by conductors of sufficient strength and current-carrying capability to discharge electrical energy to earth. "


    If the system is completely isolated from earth, then current will not flow through you to earth, because that is an open circuit. Its a method used to acheive safety in explosive atmospheres where stray earth currents are very dangerous.

    However, the reason we earth power distribution networks, and are obliged to do so by law; is because an undetected earth fault can arise. If you then become part of the circuit to earth, (ie another fault) current will flow.
     
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