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Thread: How does electricity moves through the ground? - TT Earthing Systems

  1. #1 How does electricity moves through the ground? - TT Earthing Systems 
    New Member fixiefitzy's Avatar
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    I am just starting a course to become an electrician ( 2 month in ). I like to understand how things work.

    How does the current that passes down to earth via a rod driven into the ground outside your house travel through the ground to the local transformer to complete the circuit.

    And how does it know what direction to travel through the earth?

    Would it not possibly travel to another transformer?

    (please explain simply)


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    The electrical current travels by means of ions dissolved in the moisture in the ground. In dry soil, this may not work as well. Also the ground rod has to go below the frost line, because ice is not a good conductor.

    The current does not know, but the current always has to flow in a circuit. If no current returned to the neutral of the transformer, then none could flow out through the line. You could think of the two nearby transformers as being similar to two pumps pumping water out of a pond, then returning water to the same pond. The water does not care which pump suction line it returns to, but you may be sure that both pumps will have water flowing into the suction pipe, or else nothing would be coming out.

    By the way, the current normally flows back to the transformer via the neutral conductor, not the ground. The ground path only carries current in event of a fault.


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    New Member fixiefitzy's Avatar
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    harold14370 Thank you for your explanation I think I understand it I'm based in the UK and my assumption is that by Pond you refer to our National Grid.

    I understand this only occurs in fault conditions I was interested in how under fault conditions a circuit is made so the RCD gets tripped.

    I have been looking at different bits on the web and if I have got this correct the earth likes to stay Neutral 0 current so it will pass the current up to the transformer. The amount of earth is a large expanse so the transformer must some how attract the current. Is this a correct assumption can anyone explain how this attraction works? and if so how far would it attract current from?
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    No, what I intended to do was make an analogy between a transformer and a mechanical pump, where a transformer would be like a pump and the ground would be like a pond of water, or sea of electrons, if you will. Obviously, that analogy was not a good one.

    Under normal conditions, the current flows as follows. Let's say you are using a circular saw or drill out of doors. Without a ground fault in your saw, the current goes from the pole transformer, through a circuit breaker in your home's distribution panel, then out through the circular saw, back through the distribution panel, and to the opposite (grounded) side of the transformer.

    Now let's say there is a fault in your circular saw, such that the line voltage makes contact with the chassis of your saw. There is a conduction path which goes from the saw, through your body to the wet ground you are standing on, then back through the ground to the grounded side of the transformer. Now there is more current in the line side of your distribution panel than in the other side (what we would call the neutral in the US, where we have a center tapped transformer). Your ground fault interrupting device would then trip because it detects higher current in the line side than the return conductor. In the US we would have a ground fault circuit interrupter (GFCI) on each protected circuit, but as I understand it, you in UK have a single device which monitors the current in the whole home.

    Think of the earth as one huge conductor. The current can flow any distance, but like any other conductor it does have some resistance associated with it. That resistance is not uniform throughout but varies with the moisture in the soil and other factors.

    Edit: I shouldn't have used the term "sea of electrons" which actually applies only to metals, but it kind of fit in with my water pump analogy.
    Last edited by Harold14370; November 29th, 2011 at 05:53 AM.
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    It's interesting. When investigating power outages in our area, I realized there is no ground or neutral wire in the feed to the pole transformers. There are two hot lines (two phases), and the earth ground IS the ground/neutral.

    I've been in the electrical/electronic biz for 5 decades, and never knew that!
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    Quote Originally Posted by MeteorWayne View Post
    It's interesting. When investigating power outages in our area, I realized there is no ground or neutral wire in the feed to the pole transformers. There are two hot lines (two phases), and the earth ground IS the ground/neutral.

    I've been in the electrical/electronic biz for 5 decades, and never knew that!
    Are you sure it wasn't two insulated conductors and a bare neutral conductor? That's the way mine is. Or do you mean the connection to the primary of the transformer?

    Service drop - Wikipedia, the free encyclopedia
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    No these are the feed lines. Two uninsulated lines. One goes to one transformer (with no other connection than earth ground), the other continues on to another transformer down the block. Out of the transformers, the insulated lines go to the houses (The service lines).

    220px-Polemount-singlephase-closeup.jpg

    Note the single feed line at the top. The wire attached to the case side on the right goes to earth ground, completing the circuit, at least from what I can see.
    Last edited by MeteorWayne; November 30th, 2011 at 06:28 AM.
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    Then you are referring to the primary side of the transformer. The transformer with single bushing on top as shown is used when a primary neutral wire is available. If there weren't a primary neutral wire the transformer would be connected phase to phase, which would need two high voltage connections (bushings).

    From Wikipedia:
    http://en.wikipedia.org/wiki/Distribution_transformer
    Primary
    The high voltage primary windings are brought out to bushings on the top of the case.

    • Single phase transformers, generally used in the USA system, are attached to the overhead wires with two different types of connections:
      • If a primary neutral wire is available, a 'wye' or 'phase to neutral' transformer can be used. This usually has only one bushing on top, connected to one of the primary phases. The other end of the primary winding is 'grounded' to the transformer's case, which is connected to the neutral wire of the 3 phase system, and also earth ground. This type of distribution system, called 'grounded wye', is preferred because the transformers present unbalanced loads on the line, causing currents in the neutral wire. With the 'delta' connection, this can cause variations in the voltages on the 3 phase wires.
      • If no neutral wire is available, a 'delta' or 'phase to phase' transformer must be used. This has two bushings on top which are connected to two of the three primary wires, so the voltage across the primary winding is the phase-to-phase voltage. This type is used on long distribution lines where it is uneconomical to run a fourth neutral wire.

    • Transformers providing three-phase secondary power, which are used for residential service in the European system, have three secondary windings and are attached to all three primary phase wires. The windings are almost always connected in a 'wye' configuration, with the ends of the three windings connected together and grounded.
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