From: dh0496@windstream.net   
      
        I work for a company that sells center pivot irrigation systems. A   
   common situation   
   is the pivot and electric well motor are powered from a commercial   
   utility.  The electrical service is three phase, 480 volts,  and there   
   will be 1300 feet of quad wire buried from the utility's meter to the   
   well and pivot.   
       We sometimes see that one of the underground power wires has gone   
   bad.  Someone will simply substitute the equipment ground wire for the   
   bad power wire.   People think the ground rods and earth will keep them   
   safe.  I'd like to have a short illustration showing that it won't.   
       I found a chart in an article that shows earth resistance.  Farm   
   ground is 100 ohms/meter.  Thirteen hundred feet or 396.24 meters x 100   
   ohms equals 39,624 ohms resistance in the dirt.  I added 50 ohms   
   resistance for the two ground rods that would be at the utility's power   
   pole and at the well.   
      An online Ohm's law calculator put the current flow from the well   
   motor to the utility's supply at 0.012 amps if there was a short to the   
   well motor's frame.   That wouldn't blow even the smallest fuse in the   
   equipment. Am I at all on the right track with this?   
                                                               Thanks,   
   gentlemen   
      
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