But if you measure earth resistance of the ground rod with GEC conected to it, you would have a value less than ohm even with EGC disconnected. It is because of a very large number of ground rods already connected to neutral of supply upstream getting in parallel connection with the ground rod at the trailer end, thereby lowering earth resistance of the ground rod at the trailer to less than 1 ohm!
Go back and review that logic please.
If you leave the GEC connected to the service neutral you would measure a very low resistance to earth if you use the three point fall of potential method over a few thousand foot baseline (all those other electrodes expand the sphere of influence.) Or find some other way to make a single ended measurement.
But that does not mean the the addition of a single ground rod is sufficient to make use of that low impedance.
And in fact it is the connection to the service neutral that provides the low impedance return path, not just the multiple ground points. The MGN provide a low earth impedance on the POCO side, not the customer side.
In this particular case, with the neutral and hot reversed, there is no path to earth on the trailer end except through the single ground electrode. And that by itself is almost always not good enough to operate OCPD.
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