The measurement of ground resistance for an earth electrode system 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. Since the resistance of the grounding, system can increase if the ground rods are eaten away by corrosive soils with high moisture content, high salt content, and high temperatures.
The most commonly used method of measuring the earth resistance of an earth electrode is the fall-of-potential test method. This video describes the three basic types of the fall-of-potential method:
• Full fall-of-potential
• Simplified fall-of-potential
• 62 Rule
This video describes these methods

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