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Why won't ground reroute the general home circuit?

  1. Aug 27, 2009 #1

    foo

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    For general house wiring.

    As I understand it, the ground will carry away harmful power when there is a fault in the neutral lets say a wall outlet that has a load plugged into it.

    What keeps power from going to ground normally? Is the ground only available when a load is plugged into the wall outlet thus adding the ground to complete a mini circuit within the load?
    If so, why doesn't current just flow to ground initially rather than only to neutral; why no power to both paths in such cases as well?

    Thanks in advance.
     
  2. jcsd
  3. Aug 27, 2009 #2

    Danger

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    Welcome to PF, Foo.
    I can't give you a definitive answer because I'm not an electrician. Basically, system neutral (white wire in North America) is a ground. The green or bare wire is merely an emergency back-up in case of failure in the neutral.
    Berkeman and a couple of others here can give you a much better explanation.
     
  4. Aug 27, 2009 #3

    negitron

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    Ultimately, neutral and ground are bonded together close to the load center (the circuit breaker or fuse box). The reason for keeping them separate within the building is to provide a safety for fault current but which otherwise carries zero current and has, therefore, zero volts on it. The neutral is a necessary part of the circuit, as it provides the return path for load current; however, since it IS carrying current, it also necessarily has a voltage present--this is normally fairly low since the resistance to ground is just a few ohms, but if it opens you can be exposed to line voltage. So you have two paths to ground: one to provide the return path for electric circuits and the other as a non-current-carrying safety.
     
  5. Aug 27, 2009 #4

    vk6kro

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    What keeps power from going to ground normally? Is the ground only available when a load is plugged into the wall outlet thus adding the ground to complete a mini circuit within the load?
    If so, why doesn't current just flow to ground initially rather than only to neutral; why no power to both paths in such cases as well?


    Power does not go to ground normally because it is not connected to ground.

    The load is connected between Active and Neutral.

    If there was a fault with the appliance so that power was unfortunately connected to metal parts of the appliance, then this would be dangerous for anyone who touched the appliance.
    BUT there is the ground connection connected to these metal parts and this carries away current to ground and, at the same time, it should cause a RCD or a fuse or a circuit breaker to trip, removing power from the appliance.
     
  6. Aug 27, 2009 #5

    foo

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    Thank you for the responses.

    Ok, so neutral comes in from the power lines outside the house > connects through a meter box > then through to the main breaker box > then throughout the entire house > then back to a neutral bus bar on the main breaker and then to where? What is the neutral bus bar tied to? Is it the same grounding rod or pipes that the ground is connected to?
     
  7. Aug 27, 2009 #6

    chroot

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    The power company supplies you with a hot and neutral wire, carrying current from their generators. You connect a third wire to your local ground, and also to the neutral wire out in your breaker box, and then you string all three wires all over your house.

    The essential idea is:

    1) Current normally only passes through the neutral conductor.
    2) Metal parts which may be touched by humans are connected to the ground conductor.
    3) If current ever flows through the ground conductor, devices in your breaker box sense it and turn off the power.

    - Warren
     
  8. Aug 30, 2009 #7

    foo

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    So then when the neutral wire completes its circuit it ends up at the neutral bus bar on the circuit break box right? Does this then get connected back to the neutral coming in from the power company? Is that how it completes the return path or where does this bus bar end up tying into?
    Thanks for the replies
     
  9. Aug 30, 2009 #8

    negitron

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    All three lines: the power company neutral, the building neutral and the building safety ground all get bonded to Earth via a ground rod located near where the power company drop line enters the building.
     
  10. Aug 30, 2009 #9

    vk6kro

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    Within the house, the ground and neutral wires are kept separate.

    Power only travels in the neutral and active wires.

    The ground wire only carries current if there is a fault.
     
  11. Aug 30, 2009 #10
    Hi, :smile:

    Basically, system neutral is connected with ground conductor at the sub-station end to keep the neutral conductor at ground potential in case of external faults (eg. lightning bolts on power system, etc.) to prevent the neutral from rising to dangerous voltages.

    Although , theoretically the ground wire and the neutral does perform the same function, practically, it is mandatory to have separate wire (earth wire) to safely carry fault currents away from the electrical system. This is strictly as per the dictats of the International Standards for Electrical Safety! For further details you can look up Wikipedia

    Regards,
    Shahvir
     
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