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FALL-OF-POTENTIAL METHOD TESTING PROCEDURE APPENDIX D: GROUNDING (EARTHING) ELECTRODE SYSTEM TESTING/VERIFICATION
VALID TEST GRAPH
At approximately 62% of the total distance, a
plateau or “flat spot” should be noticeable in
the plot. The resistance at this plateau is the
resistance of the system under test.
INVALID TEST GRAPH (Z-Probe Spacing)
The Z probe is not placed far enough from the
grounding electrode system.
Reposition Z-probe farther away from X
connecting point and repeat test.
INVALID TEST GRAPH (Connection to neutral)
Due to a connection that still exists to the
Power Company neutral conductor or other
utility, the resulting curve has very little change
until the point nearest the remote current
probe. No valid plateau exists.
Have connection removed and repeat test.
FIGURE D-5 TYPICAL FALL-OF-POTENTIAL TEST GRAPH RESULTS
0% 50%
Relative Distance of Y-probe Between
X-probe and Z-probe
100%
D-12 68P81089E50-B 9/1/05
System Resistance
System Resistance
System Resistance
Plateau at approximately
62% of “100%” distance
0% 50%
Relative Distance of Y-probe Between
X-probe and Z-probe
100%
0% 50%
Relative Distance of Y-probe Between
X-probe and Z-probe
100%