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Electronics Engineering QUESTION #11740
Question 1
During earth resistance measurement using the fall-of-potential method, what does a flat region in the resistance vs. probe-spacing curve indicate?
  • The test current is too high causing ground heating
  • The true earth resistance of the electrode — both auxiliary probes are outside the zone of influence✔️
  • The measuring instrument has reached its maximum range
  • A buried metallic conductor is creating measurement interference
Correct Answer Explanation
In the fall-of-potential (three-terminal) method, resistance is measured as the voltage probe is moved between the current electrode and a remote auxiliary. The plateau (flat region) in the R vs. distance curve indicates that both auxiliary probes are beyond the mutual zone of influence of the test electrode, giving a true earth resistance reading. The measurement is taken in the middle of this plateau.