How many rods are required for the fall-of-potential method to test earth resistance?

In the fall-of-potential method for testing earth resistance, three rods are typically used to ensure accuracy in the measurements taken. These rods are utilized to establish a potential difference and to help measure the earth resistance effectively.

One rod, known as the current electrode, is driven into the ground at the site of the grounding system being tested, while the other two rods serve as potential electrodes, positioned at specific distances from the current rod to ensure that the measurements taken are reliable. The distances between these electrodes are crucial; they must be far enough apart to avoid influencing the readings due to the interaction of the current flowing through the ground.

The third rod is added to help plot the potential gradient in the soil, which allows for precise calculations of resistance by taking measurements at various distances. This method can significantly reduce the influence of other nearby grounding systems on the readings, leading to a more accurate assessment of the earth resistance of the system being tested.

Therefore, the requirement for three rods in this method is essential to accurately measure earth resistance while minimizing interference.