The earth resistance can be measured by

The earth resistance can be measured by

Right Answer is:

Only (1) and (2)


Fall-of-Potential Method

  • This method measures grounding electrode resistance based upon the principle of the potential drop across the resistance.
  • It also uses two auxiliary electrodes (one current rod and the other a potential rod) that are placed at a sufficient distance from the test electrodes; a current of known magnitude is passed through the electrode under test and one of the auxiliary electrodes (current rod).
  • The drop in potential between the electrode under the test and the second auxiliary electrode (potential rod) is measured.
  • The ratio of voltage drop (V) to the known current (I) will indicate the resistance of the grounding circuit. Either a DC or AC voltage source may be used for conducting this test.

Earth tester

  • The earth resistance can be measured with the help of an Earth tester or a Megger Earth Tester.
  • This instrument is used for measuring the resistance of earth electrodes and the resistivity of soil. The preferred model is the 4-terminal type. It gives ac output.
  • It is a combined cross-coil ohmmeter (ratio-meter) and hand-driven generator of a special type so designed that alternating current is passed on to the soil while direct current is passed through the measuring instrument.
  • This instrument usually has a voltage range of 10-110 V with a current range up to 5 mA, frequency of about 92-95 Hz, ohmic range from 0-2 up to 10,000 ohms. Indigenous designs are available in the test voltage range of 50-200 V approximately.
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