Ground Resistance

10,145, 332.378 Giga Ohms.


Am I close?


Z.

NERC - Skin of the Earth (ukri.org)


Z.

Good answer Zoom, I`ve no idea.

As we move away from the sphere of influence of say an earth road then my idea is we move to very small lumps of high resistance bobbles of earth but many para paths with multitudes of cross connected series-para and para series all para together so a relatively low value I think. in one country it might be quite low at near extremes but what about between countries/continents. 


I think some on here will have some expert opinions of it.


I suppose it`s just a saturday type question

Well, if we need conductive stuff to connect England to Oz then it will have to be soil won't it? Or perhaps it could be salt water of the seas? It can't be rock or dry sand as they do not conduct very well. As for deep earth core magma, I just don't know. That reminds me of Barbarella and the Mathmos. I liked the Black Queen, very sexy.  "Hello pretty pretty" ...................."My name's not pretty  pretty my name is Barbarella.  MapJ1 mentioned a single wire transmission  system once but that used very high Voltages. Air won't conduct very well, but does carry radio signals. So, my guess is just a guess.

Single-wire transmission line - Wikipedia


Z.

I'd guess the opposite - on that the basis that the c.s.a. of the planet is very large even if it has poor conductance per unit volume it's still going to have a very low resistance overall. So even without any extra cables, I would have thought it was hardly any more than the normally measured resistances of the two electrodes added together.


Add in that much of the Earth's rocks are rich in iron and salt water is reasonably conductive.


   - Andy.

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


Probably best not to follow your nose here ebee! 


Regards


BAD

If you put two rods each 1 m long and 1 cm diameter 2 cm apart, the resistance is predominantly that of the earth between them i.e. a 2 cm length of 200 cm² CSA. Then there are parallel paths, as it were, all the way around, but they are significantly longer.


Now put the rods 1 m apart. The resistance of the bit between them is 50 times as much, but the closer parallel paths are not much longer, so the overall effect is that the resistance is not 50 times higher.


The further apart you get, the CSA of all the parallel paths comes to dominate over their length. I suspect that there comes a point where getting further apart makes very little or no difference.


Now think of a TT installation and it's EFLI. We think of the resistance of the two rods - local and transformer. We do not worry much about their distance apart.


The Earth is 40,000 km round, so if you go to the other side, the CSA at its widest point is 127 x 10⁶ km² = 127 x 10¹⁸ mm²; so if you take a slice there, it is going to have pretty negligible resistance.


Don't forget the huge amount of iron in the Earth's core.


My calculus is not good enough to work it out properly, but my guess would be of the order of 1,000 Ω.

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