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B How do you calculate voltage drop across neutral and ground?

  1. Nov 20, 2018 #1
    In our practical world, the voltage between the neutral wire and the ground is not exactly 0V, and there's some small current passing through the wire connecting the neutral wire to the ground, how do you mathematically calculate this voltage drop?
  2. jcsd
  3. Nov 20, 2018 #2


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    Would that be in a powerplant, or somewhere on the North York Moors ?

    You need something to begin calculating with -- mainly strengths and directions of stray magnetic fields, and the full layout of ground wiring that functions as antenna -- and that's generally not easy to set up.
  4. Nov 20, 2018 #3


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    There is nothing fundamental about this - it depends on the circuit and how it is being used,
    You would need to measure the resistances in the circuit and also know the likely currents that would be flowing.
    The resistances of the cables can be estimated from their lengths and thicknesses and there will probably be data about the likely resistance of the cable joints. Also, in a three phase system, there can be unbalanced neutral current at the transformer which can produce an inherent neutral voltage. Note - this remark depends on the particular supply layout and where "the transformer" happens to be. If the transformer is part of the Consumer's Installation, high imbalanced volts are very likely because there can be a big difference between the loads on the two legs of a 'split phase' system.
    But don't go there unless you want to get involved with a massive subject with many many variations. :wink:
  5. Nov 20, 2018 #4
    I thought it was a basic v=ir equation, but nope, that seems complicated
  6. Nov 20, 2018 #5


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    It requires knowledge of which R and which I. :wink:
    Thing is, in a three phase system, the Neutral conductor would, ideally, carry no current because the three phases would carry equal net (load balanced) currents. Any imbalance will cause a Neutral Voltage to appear (Unbalanced Current X Neutral line Resistance). Same in a Split Phase domestic system, where two equal loads will produce Zero Neutral current.
    But something to make you feel better is that the way the Power / Energy is metered, you only pay for the Energy you have actually used in your devices. Losses in the supply cables are, of course, paid for by somebody but that cost is divided up between all users in the unit cost. Remote users actually get pretty good value because of the Energy dissipated in their long supply cables is paid for by all of us.
    And the point made by @BvU is also relevant. EM waves are radiating away from every AC circuit.
  7. Nov 20, 2018 #6


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    Kevin is no longer with us, so this thread can be closed now. Thanks for your replies. :smile:
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