Full Fall-of-Potential Test Explained

Watch our certified Technical Trainer Gregg Wong step through a demonstration of the Fall-of-Potential ground resistance testing method using the AEMC® Instruments Ground Resistance Tester Model 6472.
Fall-of-Potential ground testing is a method used to measure the resistance of a grounding system. It is a non-destructive test that requires the system to be de-energized and disconnected. The test is performed by injecting a known current into the ground at a distance from the grounding system under test and then measuring the potential at different points between the grounding system and the injector electrode. The results of the test can be used to determine if the grounding system is in good condition and meets the requirements of the National Electrical Code (NEC) and other applicable standards.
The Fall-of-Potential ground testing method is based on the principle that the current flowing through a conductor creates a voltage drop across the conductor. The voltage drop is proportional to the resistance of the conductor and the current flowing through it. By measuring the voltage drop between two points on a conductor, the resistance of the conductor can be calculated.
Advantages of the Fall-of-Potential ground testing method:
• It can be used to test grounding systems of any size and shape.
• It is relatively inexpensive.
• It is a more accurate test to perform.
Disadvantages of the fall-of-potential ground testing method:
• It requires the grounding system to be disconnected.
• The results of the test can be affected by soil conditions.
• The test is more involved and takes more time than a clamp-on method.
Learn more about the AEMC® instruments Ground Resistance Tester Model 6472 used in this video:
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[@thisguy2909]

is the 5 % or less deviation between 50-70 the same standard for substations. surely, they are i would think anyways

[@AEMCInstruments]

In theory, yes. Substations are especially tricky to test, even in the best of conditions. IEEE 80 Standard for Substation Grounding does not always recommend Fall of Potential testing for substation grids. Suggest referring to that standard. Keep in mind, Fall of Potential testing requires the ground-under-test to be disconnected and de-energized. This is not always easily achievable with substations.