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Ground Resistance

ebee
It used to be fag packet type approximation that when measuring the earth impedance that as a very very much rule of thumb starter for ten sort of thing.

approx 80% of the total figure between two fart away points might be made up of the area around the local rod/plate/tapes etc and the other 20% between that area and all the area between them up to the area surrounding the other earthing point.

What would be a sort of max in ohms between two extremely far points example two countries ? say England and New Zealand or Oz?
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    It wil be the sum of the two electrode resistances, assuming you measured them correctly  (*) so, 2 off 4 foot rods, one in UK one in Nz, each one say  100 ohm electrode resistance then total loop 200 ohms.


    Oddly enough bits of NZ use SWER distribution, where the losses in the over head lines are higher than the losses in the ground return path.



    (*) The electrode resistance is defined as the resistance to the plate et the end of the universe more or less, but what you measure is deduced by extrapolating from 2  electrodes that are of course rather closer than that, and may not be quite right - the earth is not totally homogeneous .



    this effect that the middle thousands of km have less effect than the last hundred metres  is entirely because as mentioned above, the effective cross section of the further away equipotential slices is much larger.

    Mike.


    Note if you try to show field patterns of scale models using Teledeltos paper and silver paint, and drawing contours of equal voltage using your DMM and a felt tip pen, rather in the manner of the second year labs, while it is good fun and quite educational, you do not get the right shapes except for problems of infinite extend in one axis- on conductive paper the current divergence is  only in 2D - in real ground, currents can diverge up and down as well as out radially
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  • 0
    It wil be the sum of the two electrode resistances, assuming you measured them correctly  (*) so, 2 off 4 foot rods, one in UK one in Nz, each one say  100 ohm electrode resistance then total loop 200 ohms.


    Oddly enough bits of NZ use SWER distribution, where the losses in the over head lines are higher than the losses in the ground return path.



    (*) The electrode resistance is defined as the resistance to the plate et the end of the universe more or less, but what you measure is deduced by extrapolating from 2  electrodes that are of course rather closer than that, and may not be quite right - the earth is not totally homogeneous .



    this effect that the middle thousands of km have less effect than the last hundred metres  is entirely because as mentioned above, the effective cross section of the further away equipotential slices is much larger.

    Mike.


    Note if you try to show field patterns of scale models using Teledeltos paper and silver paint, and drawing contours of equal voltage using your DMM and a felt tip pen, rather in the manner of the second year labs, while it is good fun and quite educational, you do not get the right shapes except for problems of infinite extend in one axis- on conductive paper the current divergence is  only in 2D - in real ground, currents can diverge up and down as well as out radially
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