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Earthing in Electrical Systems

  1. Nov 6, 2016 #1

    cnh1995

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    I have a few questions about earthing in electrical systems.
    1) How can earth be used as a "conductor"? I googled its resistance and it turns out that earth resistance is not that large and it can be reliably used as a conductor. For example, I read it can be used as a return conductor in single wire power system, HVDC etc.
    Is this true? How can earth act as a conductor in long distance HVDC transmission lines? Which properties of earth are involved here?

    2) When we plug the tester in the live (hot) terminal on the switchboard, we see the neon bulb glowing. I know that the current flows to the ground through our body. But how does this current flow even when we are standing on insulating materials like concrete floor, a stool or when we are sitting on a matress etc? Also, as we go upstairs in our apartment, the distance between the switchboard and ground increases. But we still get a current through the tester when we are on higher floors. How is this possible? I read that the stray capacitance of our body is involved here but no explanation was given. Please explain this.

    3) In residential wiring, neutral wires are grounded at a particular location. Is that the only ground present in the whole residential circuit?

    (I should mention that I am from India and we have 230V, 50Hz supply with one hot and one neutral.)
    Thanks a lot in advance!
     
  2. jcsd
  3. Nov 6, 2016 #2

    rbelli1

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    Gold Member

    1) How can copper be used a a "conductor"? Which properties of copper are involved here?

    2) Look up how capacitors behave. It will be clear.

    3) Where and how the neutral is grounded will be based on your national electrical code. Usually it is grounded in the main distribution box only. Some sub distributions boxes are grounded as well. Separate safety grounds are distributed to every place the power conductors are. This may not be true in some older construction. In distribution systems there is often no separate neutral.

    BoB
     
  4. Nov 6, 2016 #3
    1) The resistance depends mainly on the type and size of electrodes used. An example of an Earth Return system is an under sea telecom cable, where a sea electrode is used at each end and the amplifiers along the cable are powered by current fed down the cable. Notice that the current in the sea follows the cable - it does not wander off all over the planet.

    2) The body has about 100pF capacitance to the rest of the Universe. This amounts to about 10 MegOhms at 50 Hz, low enough to allow the neon to light.

    3) I don't know Indian wiring practice, but in some countries the Neutral is grounded at the sub station can provide a safety Earth (Ground) for the premises.
     
    Last edited by a moderator: Nov 6, 2016
  5. Nov 16, 2016 #4
    Earthing is very necessary in any electrical power system. One of the main purpose of electrical earthing is to protection. There are several types of earthling systems use in the world such as TT earth System, TN-C_S earth systems ect.
     
    Last edited by a moderator: Nov 16, 2016
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