Neutral and earth @ distribution level

Discussion in 'General Electronics Chat' started by Bibbster, Aug 1, 2013.

  1. Bibbster

    Thread Starter New Member

    Mar 28, 2013
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    Hey guys. A little confused here and google is just confusing me more so I thought I'd come to the experts for help.

    Now at distribution level we can have our 3 phases (live) and another neutral core with a earth sheath surrounding the wire this is known as SNE( separate neutral earth) and we can also have PME( protective multiple earth ) which is earthed periodically from the neutral

    Now this is where I become unable to comprehend it. At distribution level what is the function of the earth and neutral and when they are combined (PME ) how do they function?

    P.S. I'm from uk so may use different terminologies.
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    In N.A. there is Multi-Grounded Neutral conductor where periodic grounding of the neutral occurs to retain the integrity of the Earth Ground, this is carried out at no more than every 400m.
    Initially the Safety Earth ground reference will be from the star point of any distribution transformer.
    Not sure if this the application you are referring to in the UK?
    Max.
     
  3. Bibbster

    Thread Starter New Member

    Mar 28, 2013
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    Yeah, it will come from the star point of a transformer then be grounded every so often. When will the neutral and earth be used e.g. Under what sort of conditions ?
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Do you mean under what conditions are is the neutral periodically re-referenced to ground?
    There are a few different ones, one being throughout any distribution over 1Kv.
    There are some low voltage examples such as ground mesh used in buildings housing sensitive electronic equipment.
    If you want an in depth explanations on grounding I suggest Soares Book on Grounding, published by International Assn of Elec. Inspectors.
    The NEC uses it for a reference, but most apply also to the UK.
    I picked up a practically new copy on Abe Books clearing house for $1.00!
    Max.
     
  5. Bibbster

    Thread Starter New Member

    Mar 28, 2013
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    No,no I'm meaning when will a neutral and earth wires be utilised spat dist level. I understand in houses etc neutral acts as return path and earth will carry any fault current but I just can't visualise this at at dist level :(
     
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I am still not sure what your question is, if it is the general concept of the use of Earth Ground then it is simply the principle is that no potential shall exists between the the neutral and ground conductor for safety purposes.
    The source of the grounded neutral is usually always at the distribution source, in your case of domestic supply, the star point of the 3ph transformer.
    At one time in the UK, this was the only ground point at the source and a ground was not delivered to a residence, the ground was re-referenced by connecting the ground conductor to an existing metallic water supply or equivalent and relied on ground conduction back to the supply transformer.
    Later when metallic water pipes fell out of favour in preference to plastic etc, it was mandatory to install a ground rod and GFI or ELT at these residences.

    Ref:
    It was initially theorized that the earth was an electrically neutral body, i.e. an equal number of negative and positive charges are distributed throughout the earth at any given time.
    Being electrically neutral, earth is considered to be at zero potential and establishes a convenient reference frame for voltage measurements and safety purposes.
    Noting that voltmeters read only the difference in potential between two points, absolute measurements can be made by using earth as a reference.
    Max.
     
    Last edited: Aug 1, 2013
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