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Understanding Earth Ground

Discussion in 'General Electronics Chat' started by wutever0, Aug 20, 2017.

  1. wutever0

    Thread Starter New Member

    Aug 20, 2017
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    I have a little confusion regarding how "Earth Ground" (as referenced in here) works and I searched around but I haven't had a good explanation. I'm going to take this point by point to kind of wrap my head around this.
    1 - My understanding is that the Earth is a very good conductor of electricity.
    2 - Also I was under the impression that the Earth acts as an infinite source and/or sink for electrons. Is that correct?
    3 - If so, wouldn't that mean that a battery which is connected directly, at its negative terminal, to the Earth, by a wire and not connected to anything else on the other end, wouldn't that battery lose charge immediately since the Earth acting as an infinite sink of electrons be a non-resistive destination for the electrons?
    4 - Wouldn't that also mean that if a closed-loop circuit is earth-grounded, and depending on the point which we are grounding, wouldn't it mean we would be interfering with the path the electrons would take since we are introducing a new path with very low resistance?

    Sorry if the questions are extremely silly. It's a first step to trying to understand how Earth Grounding protects us.
    Many Thanks
     
  2. SLK001

    Senior Member

    Nov 29, 2011
    1,440
    591
    1) No.
    2) No.
    3) See #2.
    4) And no.

    We use earth as a ground reference, because we "stand" on it. We want to be at the same potential as what we stand on to minimize the chances of electricity being more attracted to us than the earth, as a whole. The earth is a conductor, just not a very good one - also, the circuit containing the earth is not a reliable one, since different resistivities exist in different strata. Equipment is grounded to earth, because you wouldn't want its ground to be at a different potential than what you are standing on, or earth. If it wasn't properly earth grounded, you could potentially "complete the circuit" if you touched its ground while standing on earth - while can often be fatal.
     
  3. MaxHeadRoom

    Expert

    Jul 18, 2013
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    What you need to get is a copy of The Book on Grounding by Eustace Soares, it is used as a reference for NEC/CEC etc and is a world wide standard.
    Also. Ground Practices
    Max.
     
  4. crutschow

    Expert

    Mar 14, 2008
    23,124
    6,858
    No.
    The first rule of circuits is that the electrons need a complete path to flow.
    Electrons cannot move in or out of the battery with only one connection.
    You must have a connection to both battery terminals.
     
  5. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I see the U of Penn link is broken, this is the gist of it.
    Max.
     
  6. Tonyr1084

    Distinguished Member

    Sep 24, 2015
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    #2 and #3: The earth is not an infinite source or sink. Therefore a battery sitting on the ground would not lose its charge. Electrons don't flow just because they can. There has to be a reason for them to flow. In other words, using the battery analogy, the charge at the negative end of the battery wants to go to the positive end of the battery. Why? Because the positive end of the battery is devoid of electrons (having the negative charge), and those electrons will only go to where there's a void (to the positive end). So grounding one end of the battery - EITHER end - will not drain the battery. However, grounding BOTH ends will. And in some cases in a rather spectacular display of light and heat.
     
  7. ArakelTheDragon

    Well-Known Member

    Nov 18, 2016
    1,262
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    To put it simple:
    Ground has a very low resistance about "10 on -7" and electricity goes through the lowest resistance like the student. Instead of passing through a 1000Ohm human, it prefers to go to ground. Its not a guarantee that it wont pass through you as well so dont try!

    You also need to know the difference between "AC" and "DC" current. If you connect an "AC" wire to ground, electricity will flow (by ground I mean a stick of iron buried in the ground). If you connect a "DC" battery nothing will happen. The battery needs both ends connected for electricity to flow.
     
  8. MaxHeadRoom

    Expert

    Jul 18, 2013
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    "If you connect an "AC" wire to ground, electricity will flow (by ground I mean a stick of iron buried If you connect a "DC" battery nothing will happen."
    Not sure I understand that at all?
    BTW here a "stick of iron" is a copper coated ground rod, at least 6ft long .
    Max.
     
  9. WBahn

    Moderator

    Mar 31, 2012
    24,562
    7,700
    You have a couple of misconceptions that are interacting, so let's see if we can chip away at them.

    Imagine a fluid system in which you have a pump that draw fluid up out of a tank, pressurizes it and sends it into a system of pipes that then use that fluid to do a variety of things, perhaps lift loads or turn motors, at which point it is returned to the tank. In many hydraulic systems the tank is sealed and what is flowing out of the tank is, on average, equal to what is flowing back into the tank.

    Now imagine that our "tank" is a large lake or even an ocean and we separate the inlet to our pump and the return pipe from our system by a long distance. We are still always putting back the same amount of fluid we are pulling out, just in very different locations. The fluid that is returned to the lake (or an equal volume of other fluid in the lake) still has to eventually make its way over to the pump inlet to keep things balanced, but the amount of fluid in the lake is so large that we can't even detect this motion. This is a situation comparable to long haul DC power lines that pull electrons out of the ground one place and push them into the ground thousands of miles away. There IS a return current through the ground, but it is so small once we get any distance from the entry/exit points that we can't detect it.

    Now imagine that our inlet was in one lake and our outlet was in another, such that the fluid being returned to the second lake couldn't make it back to the first lake. As time goes on, the level of the lakes would change and it would get harder and harder to pump more fluid from the lowering lake and discharge it into the raising lake.

    Now imagine that our pump was AC, meaning that it pulled a bit of fluid up, doing some work, and then pushed it back down, doing some more work. At each entry/exit point we would just be moving the same fluid in the vicinity of the pipe back and forth and there would be no need for any fluid to actually flow between the two points. We could, in fact, put the inlet and outlet in two completely different and isolated lakes and run the system indefinitely without changing the overall level of fluid in either lake. The same is true with AC currents in a long haul line. This is where the notion of an "infinite current sink" comes from.

    As for a connection to ground draining a battery or not needing a complete circuit when one point is connected to ground, perhaps the following blog might help:

    https://forum.allaboutcircuits.com/blog/a-battery-isnt-a-capacitor.588/

    The bottom line is that as soon as any net charge flows onto or off of a circuit or component (from or two single ground connection, for instance), the circuit develops an overall net charge that tries to undo this. The forces involved build up rapidly with even just a minute amount of charge flow so that any such flow stops almost as soon as it starts.
     
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  10. ArakelTheDragon

    Well-Known Member

    Nov 18, 2016
    1,262
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    Yes, thats what it normally means, but to tell the truth an old iron stick thats 3 feet in the ground will also do, but you cant use as much electricity, because it becomes dangerous.

    The power electronics (middle voltage electronics today) consist of 3 wires ("0", phase and ground), only the phase wire carries the electricity, the rest are for safety reasons or for reducing the losses with the generator. Even if you dont have "0" but you connect the wire to ground, electricity will flow.
     
  11. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I am well aware of earth grounding in setting up ground mats for sub stations etc. the statement I have issue with is "if you connect AC to ground a current will flow, a DC battery nothing will happen"??
    Max.
     
  12. WBahn

    Moderator

    Mar 31, 2012
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    Put a current meter around that neutral wire (which I think is the one you are calling "0") and you will quickly learn that if current is flowing in the line wire (what you call phase) then current is flowing in the neutral wire. In fact, that is how ground-fault interrupt circuits work, by sensing even small differences in the difference between these two wires.
     
  13. WBahn

    Moderator

    Mar 31, 2012
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    What is "10 on -7"?

    You need both connections for either. Look at the other end of that "AC" wire that you've shoved into the ground (i.e., the other side of the generator/transformer). Guess what? It's shoved into the ground!
     
  14. ArakelTheDragon

    Well-Known Member

    Nov 18, 2016
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    But you can drain current even if you dont have a "0" wire. The defences used are test the current in the "phase" wire and "0" or "ground", meaning you can test between "phase" and "ground".

    There is current flowing through the "0" wire, that I admin, but even if there isnt a "0" wire, and you only have "phase" and "ground" your consumer (appliances) will still drain the current normally.
     
  15. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Define what is the "0" wire?
    Your country of origin would help as the terminology is strange!.
    Max.
     
  16. ArakelTheDragon

    Well-Known Member

    Nov 18, 2016
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    If you have the manual skills and technical safety knowledge, try connecting a light bolt between the "phase" and "ground" and you will see that you dont need the "0".

    And yes I know the generator is connected to ground, if you write the circuit "generator - ground" , "device - ground" you will see it should work.
     
  17. ArakelTheDragon

    Well-Known Member

    Nov 18, 2016
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    Its a standard 3-wire system: "0", "phase", "ground", I am from Bulgaria, but I think all of Europe uses this system.

    If you connect 1 end of the DC battery to ground, nothing will happen, if you connect both ends than yes it will work, and like mentioned in the previous post dont do it!
     
  18. ArakelTheDragon

    Well-Known Member

    Nov 18, 2016
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    If you have the wires at your home, the green-yellow one should be "ground", connect the phase to a light bolt and then to ground with a switch and see if it will work.
     
  19. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Sorry, doesn't make sense, AC or DC you need both in both cases.
    With AC your service provider has already connected/referenced the supply origin to earth ground.
    Max.
     
  20. WBahn

    Moderator

    Mar 31, 2012
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    That's because the "0" and the "ground" wire are BOTH connected to the other side of the generator/transformer. The "0" wire (what we call the "neutral") is a direct, metal-conductor connection while the "ground" wire is an earthed-safety ground that is ALSO a direct, metal-conductor connection to the neutral at one point in the system (in the U.S. and many other places, it is at the service entrance). The intent is for the "0" wire to carry the current under normal conditions and the "ground" wire to only carry current under fault conditions. Many of those fault conditions do not depend and are not affected by whether the system is grounded to the Earth. But some of them do.

    When you connect your "light bolt" (as opposed to dark bolt? or a heavy bolt?) between the phase and ground, you are creating a direct short, via metal conductors, across your supply. It doesn't matter whether the ground wire is connected to Earth or not.

    Do you mean "light bulb"? Same thing (except now it isn't a short). It will work regardless of whether anything is connected to Earth because the "ground" wire and the "0" wire are physically connected to each other at some point in the system.
     
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