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Just one hot with no neutral to main lugs

  1. Jan 17, 2010 #1
    This is a theoretical question about completing a circuit and trying to understand what a main panel ground rod does.

    The question is:
    Could you run just one hot wire (not in a conduit, but in free air) without an accompanying neutral to the lug of the bus bar in a main panel. The neutral bar in the panel is connected to the ground bar which in turn is connected to a ground rod in the earth. That way the breaker gets electricity to feed the branch circuit and the neutral from the branch circuit is connected to the neutral bar which is connected to the ground bar and then to the ground rod. Would this complete the circuit in order for a light bulb to burn?
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  3. Jan 17, 2010 #2


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    One hot wire from your meter to the main panel and then a neutral tied to ground only, is that what you mean?
  4. Jan 17, 2010 #3
    In short, the main panel ground rod provides a reference voltage for the system, and a controlled path for current under fault conditions.

    The way I understand your description would not work. The current that powers the light bulb you speak of still needs to make it's way back to the original generator in some shape.
  5. Jan 17, 2010 #4


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    The circuit would be completed through the soil. However, the bulb would not likely burn at full intensity due to some of the voltage being dropped across the soil between the ground rod at the service at your residence and the ground rod at the transformer. If this is a question of whether the earth can 'suck up' the current from anywhere, then the answer is no.
  6. Jan 17, 2010 #5


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    It is possible and was done for some early electric trains.
    But it's not a good idea. For large currents you can cause electrolytic corrosion in any buried metal nearby
  7. Jan 17, 2010 #6


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    Ground rise potential is the term when you have a high voltage transmission line come in contact with the earth. When I was working for a power company, earth resistances were measured around substations to see what potentials would occur if a line went down. There can be enough potential difference that you can get a shock by taking a step of a few feet.
  8. Jan 18, 2010 #7
    Yes, I am asking if putting a light bulb between a hot conductor and another conductor that is stuck into the earth, would cause the bulb to burn or allow a circular saw to run.

    I guess my real question is whether or not electricity has to return to a man-made transformer in order to complete a circuit or if electricity will naturally return into the earth, thus completing the circuit

    Assuming no people were walking nearby and using 120v, would that potential difference allow you to burn a light bulb or run a circular saw? I guess my real question is whether or not electricity has to return to a man-made transformer in order to complete a circuit or if electricity will naturally return into the earth, thus completing the circuit.

    Thanks to all for your interest and your replies.
    Last edited: Jan 18, 2010
  9. Jan 18, 2010 #8


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    The detailed answer depends upon the exact wiring of your supply transformer but, as the Neutral is at or near Earth potential, a current will flow from the Live to Earth, through a lamp or any device. The Neutral must be connected to Earth at some point back at the substation or generating station (that is the only way its potential is near (/ equal to) Earth potential. If it were not, L and N potentials would just be 'floating' at an unspecified potential with respect to ground (but with their 240 or 120V separation). If you measure the N volts in your home, they will probably not be at zero - this will be because of finite resistance in the N cable or unbalance in the three phase load back at the supply, if that's the way it happens to be done in your area. I understand that in the US, they often use single phase transformers to supply individual properties from a high voltage supply line. Any earth connection in such an arrangement will surely be poor quality as, to do it better would involve diging a big hole and sinking a good Earth spike at every pole with a local supply hanging off it. But the resistance in your 'unofficial' connection via the Earth will be much higher than that of your nice fat N wire. You will lose (and pay for) energy, dissipated by the current flowing through this Earth resistance. Plus there could be a serious safety issue, as has be said earlier, particularly if the ground around your earth spike goes dry. This could bring the spike potential to a lethal value if you are drawing a high current with a heavy load.
  10. Jan 18, 2010 #9
    There is (at least) one context in which an Earth current return is routinely used in modern practice, namely the Sea Earth return for the DC power used to international submarine telecommunications cables.

    A typical transatlantic system uses about 1A and 10kV to run the line repeaters, which are all connected series. The cable has only one useful conductor, so the return is via the Sea.
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