IEEE 81 fall-of-potential and Wenner methods

Earth Resistance and Soil Resistivity Report Format, Free PDF

Page 1 is the electrode test with a printed graph for plotting the plateau. Page 2 is the Wenner soil resistivity worksheet with a depth correction table and a single-rod estimate.

  • Free
  • No sign-up
  • A4, 2 pages
  • Formulas and limits included
Preview of the Earth Resistance and Soil Resistivity Report form
Download the PDF formA4, 2 pages

Print it at 100 % on A4. Page 1 is the form you fill in. The next page is the worksheet and reference.

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What is inside

  • Fall-of-potential readings at 10 to 90 % of the E to C distance, with the 52, 62 and 72 % plateau check rows marked
  • A printed graph with the 52, 62 and 72 % positions drawn on it, so a flat region is easy to see
  • Result boxes for the plateau check, the spacing check, the seasonal factor and the pass or fail against your permitted value
  • A Wenner worksheet for up to 8 spacings, with a depth correction factor table for b / a from 0.01 to 0.30
  • The Dwight single-rod formula with a worked example, for comparing an estimate with your measurement

How it was checked

The depth correction factors are calculated from the exact Wenner relation, which reduces to 2πaR when the probe depth is zero. The 5 % plateau tolerance and 5 × L spacing are practical guides, not limits from a standard.

Related

Common questions

What is the 62 % rule in earth testing?

In the fall-of-potential method the potential spike is placed at 62 % of the distance from the electrode to the current spike. The reading there is close to the true resistance when the soil is uniform. The form also records 52 % and 72 % to check that the readings agree.

How do I know the earth test is valid?

If the readings at 52, 62 and 72 % agree closely (the form uses 5 % as a practical guide), you are on the flat part of the curve and the test is good. If they do not, move the current spike further out and repeat.

Using the form

  • Limits and constants come from the standards named above, as commonly quoted. Check them against the edition you work to, and use the stricter of those and your specification.
  • Where a value is a common guide rather than a limit from a standard, the form says so.
  • This is a calculation aid for qualified people. It does not replace the standard, the instrument manual or your site safety procedure.

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