From: dh0496@windstream.net   
      
   On 1/23/19 9:38 PM, Rheilly Phoull wrote:   
   > On 24/01/2019 9:17 am, Dean Hoffman wrote:   
   >>      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?   
   >>                                  
   Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â  Thanks,   
   >> gentlemen   
   >>   
   >>   
   > Is the motor submerged or above the water ?   
   > If it was submerged it would be in a good earth and thus should blow a   
   > line fuse. If not it would come down to how good the remote earth stake   
   > was.   
   >   
          The irrigation well motors in my area are above ground.  They   
   range in size from 60 to 100 hp.     The center pivots have several   
   motors ranging in size from   
   1/2 hp. to 2 hp.   
      
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    * Origin: you cannot sedate... all the things you hate (1:229/2)