Measurement of Earth Resistance

Measurement of Earth Resistance is a vital part of the maintenance of any electric installation. The function of a sound earthing system is to ensure that all electric equipment are connected to the ground potential. Hence, a well-maintained earthing system ensures the proper functioning of protection systems, absorbs electrical noise and provides safety to operating personnel. The earth resistance is measured using an earth meg-gar.

“Fall of Potential” Method: The Earth resistance is measured using the “Fall of Potential” Method. The method works by injecting a constant current between two spikes which are inserted into the ground and measuring the voltage at points between them (as shown in the figure) The “Fall of Potential” Method is a three terminal test. The electrode whose earth resistance is to be measured is disconnected from the system or earthing grid. The earth meg-gar has a current terminal, a voltage terminal and a common terminal. The common terminal is connected to the electrode,