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Fall-of-potential C2 distance

    #1
  1. Join Date
    May 2016
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    Fall-of-potential C2 distance

    How do you figure out the distance required for a 3-point fall of potential test? I've heard you should drive your C2 anywhere from 3 to 10X the diagonal of the grid but I've seen other literature that give tables showing different values based on different distances.

    To keep things simple, let's say we had a building that was 100' x 200', how far out would you take your leads?

    Click image for larger version. 

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    This slide shows 10X diagonal.

    Click image for larger version. 

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    This slide shows non-linear percentages.

  2. #2
  3. Join Date
    Apr 2018
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    Quote Originally Posted by marvinray View Post
    How do you figure out the distance required for a 3-point fall of potential test? I've heard you should drive your C2 anywhere from 3 to 10X the diagonal of the grid but I've seen other literature that give tables showing different values based on different distances.

    To keep things simple, let's say we had a building that was 100' x 200', how far out would you take your leads?

    Click image for larger version. 

Name:	ground-resistance-measurement-22-638.jpg 
Views:	16 
Size:	60.3 KB 
ID:	184
    This slide shows 10X diagonal.

    Click image for larger version. 

Name:	Fall+of+Potential+Testing.jpg 
Views:	13 
Size:	91.4 KB 
ID:	183
    This slide shows non-linear percentages.

    Extract of IEEE Std 81.2-1991
    it states to use 6.5 times the substation diagonal length/distance


    Click image for larger version. 

Name:	ground grid dist.PNG 
Views:	1 
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ID:	267

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