Grounding System Testing

Grounding System Testing from Power Distribution Systems, LLC

The measurement of ground resistance for an earth electrode system is extremely important. It should be done when the electrode is first installed, and then at periodic intervals thereafter. This ensures that the resistance-to-ground does not increase over time.

There are two proven methods for testing an electrical grounding system:

3-point or Fall-of-Potential Method

This test requires complete isolation from the power utility. Not just power isolation, but also removal of any neutral or other such ground connections extending outside the grounding system. This test is the most suitable test for large grounding systems but also suitable for small single grounding electrodes.

The 3-point or fall-of-potential method is used to measure the resistance-to-ground of existing grounding systems. The two primary requirements to successfully complete this test are the ability to isolate the grounding system from the utility neutral and knowledge of the diagonal length of the grounding system.

Induced Frequency Test or Clamp-On Method

This test can be performed while power is on and requires the utility to be connected to the grounding system under test. This test is accurate only for small electrodes, as it uses frequencies in the kilohertz range, which see long conductors as inductive chokes and therefore do not reflect the 60 Hz resistance of the entire grounding system.

One of the newest test methods for measuring the resistance-to-ground of a grounding system or electrode, the Induced Frequency Test uses a special transformer to induce an oscillating voltage into the grounding system. Unlike the 3-point Test which requires the grounding system to be completely disconnected and isolated before testing, this method requires that the grounding system under test be connected to the electric utilities grounding system to provide the return path for the signal.

PDS uses both methods

Looking at the big picture, both types of testing have unique strengths. They are by no means competing or mutually exclusive technologies. For their effective use, you must understand their differences. Merely clamping on to any accessible point in an electrical grounding system does not constitute effective ground testing. A well-equipped ground-testing program from Power Distribution Solutions, LLC will take advantage of both technologies.

When you need to know the value of your system with ground testing, give us a call at 770-732-8824 or email us at

If you are looking for a quality electrical and mechanical services enterprise offering a diversified toolbox of solutions for systems dependability, systems operating programs, and systems safety standards…you found it.  Give us a call today at 770-732-8824 and see what Power Distribution Solutions, LLC can do for you!