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GSM-204-423
Fall of potential
This method of testing is used for measuring resistance of earth electrodes but
is only practical on single earth electrode systems.
Drive the current test spike and potential spike into the ground as shown in
Figure 2-5. Perform the three resistance tests and check that the average of the
three tests is less than 10.0 ohms.
61.8% Rule
This method applies when the three electrodes (earth, potential and current) can
be positioned in a straight line, the soil is homogenous and also when single
electrode systems are being used.
Set up the test equipment as shown in Figure 2-5 with the potential spike placed
at a distance of 61.8% of the distance from the earth electrode to the current
test spike. A greater accuracy can be achieved by increasing the number of
readings.
Slope method
This method applies to large earth systems. Refer to Figure 2-5, but insert the
potential spike at a number of points between the earth system and the current
spike. A minimum of six readings must be taken to plot a graph and this graph
compared to published tables to calculate the resistance.
On completion of testing, complete and sign the earth electrode test
documentation (Forms of Completion and Inspection Certificate).
31st Oct 01
3 m
3 m
(Test 2)
(Test 3)
Current
test
spike
Figure 2-5 Earth electrode test setup
Installation & Configuration: Horizon macro outdoor
68P02902W03-A
CONTROLLED INTRODUCTION
PAT Tester
C1/P1
C2
P2
Potential
spike
50 m
(Test 1)
Earthing the site
25 m
Earth
electrode
Inst. 2–15
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