100721-1130 EST
gws:
I do not understand your question either.
If your question ultimately is related to people getting shocks, then some form of GFCI might be important.
How could you measure the resistance of an EGC? If it is part of a single circuit from the main panel to the point where you want to make the measurement, and no other loads or connections exist to the EGC or neutral, then with no load measure the voltage between neutral and the EGC. I will assume the result is very close to 0.0 millivolts.
I am assuming you are talking fairly long runs, maybe 200 to 1000 ft. Suppose copper wire, size is #6, and we are at a 1000 ft destination, then the 20 deg C resistance is about 0.395 ohms. 10 amperes thru this is a voltage drop of 3.95 V.
Put your volt meter between neutral and EGC, and from a hot wire to EGC supply 10 A and you should read about 4 V. This is using the neutral as a long test lead. Because the neutral and EGC are very close together the 1 turn loop formed has little cross sectional area and therefore the voltage induced in this loop from the current flow is probably negligible.
Next you can switch the current to the neutral and measure the neutral resistance with the EGC being the long test lead.
Now suppose there is a 30 A breaker supplying this circuit. It will be worse if the breaker is larger. A 30 A breaker may take a very long time to trip at 30 A or may never trip. 30 A thru my above example would produce about 12 V on the EGC relative to the surrounding wet earth. Entirely possible this could be lethal to a person soaked in conductive water.
Not that you eliminate EGCs, but much better protection will be provided by the addition of sensitive GFCIs.
What happens to the equipment chassis potential if all hots, neutral, and EGC are the same wire size and material, and a dead short occurs between a hot and the EGC? The equipment chassis voltage relative to earth will rise to about 1/2 of the hot supply voltage until the breaker trips.
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