The earth resistance can be measured by
The earth resistance can be measured by
Right Answer is:
Only (1) and (2)
SOLUTION
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.