Touch potential

I'm learning at least a little bit about touch potential. Most of what I've found is related to the guys who work on power lines. I did
find this sketch of a guy touching a lamp post with 120 volts on it. The touch potential at the ground rod is 0. It increases as one gets farther from the ground rod. Sketch here: http://preview.alturl.com/2fywm I want to make something similar but relate it to irrigation wells and center pivot irrigation systems. Those are powered by three phase 480 volts. A picture here: http://preview.alturl.com/9ezbs The towers are typically 180 feet apart. The motors that drive them are three phase 480 and usually 1/2 to 1 horsepower. Suppose there is no equipment ground in the underground wires supplying power to the machine. One of the tower motors is shorted to its casing. Would it be fair to say the touch potential is the full line to ground voltage if a person touching it is at one of the towers? The tower nearest to the ground rod would be that 180 feet. The center point is bolted to the concrete pad and there is a ground rod there. This scenario happens now and then when one of the underground power wires goes bad. Someone will just substitute the original equipment ground for the bad power wire. He thinks the ground rods make things safe and/or he will fix it right someday. There's that old Credence Clearwater song Someday Never Comes.
Thank you.
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