Amprobe GP-2 Geo-Test - Manual (Page 37)

GP-2 GeoTest
EN - 37
For large earth plants
This procedure is also based on the voltamperometric method, but it is mainly used when
it is difficult to position the auxiliary current rod at a distance corresponding to five-times
the diagonal of the area of the earth equipment. Position the current probe at a distance
equal to the diagonal of the area of the earth equipment (see Figure 6). To make sure that
the voltage probe is positioned outside the area affected by the rod under test, take more
measurements, first positioning the voltage probe halfway between the rod and the current
probe, then moving the probe both towards the earth rod and towards the current probe.
Black
Green
Red
Blue
Figure 6: earth resistance measurement (voltamperometric method for big earth
plant)
Use several rods in parallel and
moisten the surrounding ground if
the instrument is not able to
supply the current necessary to
perform the test because of an
high earth resistance.