Illustrated below are applications where the earth clamp tester is most suitable to be employed.
Earth resistance measurement of a pole earthing electrode:

Earth resistance measurement of a pole earthing electrode in Railway:

Earth resistance measurement of an earthing electrode in a street lighting system:

Earth resistance measurement of an earthing electrode in a lightning protection system:

 

Earth resistance measurement of a simple earthing system using the main water pipe:

The above figure illustrates the measurement of an earthing system in an installation where a metallic water pipe originating from an extensive underground system is available. However the main earthing conductor (MEC) has to be temporarily disconnected and a temporary link between the water pipe and the earthing system introduced. (Refer to safety warnings below).
Therefore, under these circumstances, the reading obtained using the Earth Clamp indicates the resistance of the simple earthing system under test.

Safety Warnings!
To avoid possible risk of electric shock due to voltage difference between:

• Main earth bar (Meb) and Mec
• Earthing system and metallic water pipe switch off the power supply prior to implementing the temporary measures. The power supply should only be restored after the temporary measures have been removed.

Earth resistance measurement of a simple earthing system using the Neutral conductor:

 

The above figure shows a possible field application when a very low Ro is present. Ro is normally very low since the earthing system of a transformer is usually bonded to the earthing system of the other transformers.
Given this situation the Earth Clamp can be used to measure the resistance of a simple earthing system. However the Mec has to be temporarily disconnected and a temporary link introduced between the neutral conductor and the earthing system (Refer to safety warnings below).
Therefore, under these circumstances, the reading obtained using the Earth Clamp indicates the resistance of the simple earthing installation under test.

Safety Warnings!
To avoid possible risk of electric shock due to voltage difference between:

• Mainearth bar (Meb) and Mec.
• Earthing system and neutral conductor switch off the power supply prior to implementing the temporary measures. The power supply should only be restored after the temporary measures have been removed.