Ground resistance testing – 62% simplified fall of potential method?

Ground resistance testing, specifically the fall of the potential method, is a common technique used to measure the electrical resistance of the grounding system in electrical installations. The fall of the potential method involves passing a known current through the grounding system and measuring the voltage drop across the ground to determine its resistance. The 62% simplified fall of the potential method is a variation of this approach.

Here’s a simplified explanation of the 62% fall of potential method for ground resistance testing:

1. Setup:

   • A current is injected into the ground using a current source, typically by applying a voltage between a current electrode and a grounding electrode.
   • Voltage measurements are taken at a certain distance away from the grounding electrode using a potential (voltage) electrode.

2. Measurement Points:

   • Three key measurement points are considered: A, B, and M.
     • Point A is at the grounding electrode where the current is injected.
     • Point B is at a distance away from the grounding electrode where voltage is measured.
     • Point M is the midpoint between A and B.

3. Percentage Calculation:

   • The 62% simplified fall of the potential method involves calculating the ground resistance based on the voltage drop between Points A and B.
   • The resistance is determined at the point where the voltage has fallen to 62% of the initial value.

4. Mathematical Relationship:

   • The relationship between the resistances at Points A and B can be expressed as: R=0.62xR(AB)​
   • Where R​ is the ground resistance, and R(AB)​ is the resistance measured between Points A and B.

5. Equipment:

   • Specialized instruments, such as ground resistance testers or earth resistance meters, are used to inject the current and measure the voltage drop.

6. Interpretation:

   • The lower the ground resistance, the better the grounding system performance. A low resistance indicates efficient dissipation of fault currents into the ground, reducing the risk of electrical shock and equipment damage.

7. Factors Affecting Accuracy:

   • Proper spacing and alignment of the current and potential electrodes are crucial for accurate measurements.
   • Soil conditions, moisture content, and temperature can also impact the accuracy of the measurements.

It’s important to note that while the 62% simplified fall of potential method is widely used, there are other methods, such as the 100% fall of potential method, the Wenner method, and the four-point method, each with its own advantages and considerations. The specific method chosen depends on the requirements of the application and the accuracy needed for the measurement.