Application Note

What are the methods of earth ground testing?
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DISPLAY
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1625-2
ADVANCED EARTH / GROUND TESTER GEO
E S HES
AC
Rresistance
300kΩEarth/Ground Resistance 300kΩ
DC
Resistance 3kΩ
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Setup for soil resistivity test-
ing using the Fluke 1623-2 or
1625-2.
7
How do I measure soil resistance?
To test soil resistivity, connect the ground tester
as shown below.
As you can see, four earth ground stakes are
positioned in the soil in a straight line, equidis-
tant from one another. The distance between
earth ground stakes should be at least three
times greater than the stake depth. So if the
depth of each ground stake is one foot (30 centi-
meters), make sure the distance between stakes
is greater than three feet (91 centimeters).
The Fluke 1625-2 generates a known current
through the two outer ground stakes and the
drop in voltage potential is measured between
the two inner ground stakes. Using Ohm’s Law
(V = IR), the Fluke tester automatically calculates
the soil resistance.
Because measurement results are often dis-
torted and invalidated by underground pieces
of metal, underground aquifers, etc. additional
measurements where the stake’s axis are
turned 90 degrees is always recommended. By
changing the depth and distance several times,
a profile is produced that can determine a suit-
able ground resistance system.
Soil resistivity measurements are often cor-
rupted by the existence of ground currents and
their harmonics. To prevent this from occurring,
the Fluke 1625-2 uses an Automatic Frequency
Control (AFC) System. This automatically selects
the testing frequency with the least amount of
noise enabling you to get a clear reading.