This method is useful when the auxiliary earth electrodes cannot be driven into the ground and when an estimation of earth resistance is acceptable. Thus instead of the auxiliary earth electrodes one uses existing earth systems (with a sufficiently low earth resistance) such as:
Common earth for commercial power supply, buried metal pipes like main water pipe a lightning protection electrode on buildings With this method, P and C terminals of the earth tester should be shorted together. Connect the P terminal to the existing earth system and E terminal to the earth electrode to be measured.
Then measure the earth voltage and also the earth resistance.
When using the simplified measurement method, the resistance re of the existing earth system to which P terminal is connected is added to the resistance Rx of the electrode under test E, and displayed as the measured result.
Re (measured value) = Rx + re
If the value of re is already known, deduct it from the measured value Re to determine Rx value.
Rx= Re – re

Example of simplified measurement using the common earth of commercial supply.

Notes and safety warnings:

• The earthing system under test must be far enough away from the earthing system of a commercial supply to be outside its sphere of influence.
• The earth resistance re is normally very low since the earthing system of a commercial supply is usually bonded to the earthing system of the other power transformers (so called common earth). Given this situation the earth tester can be practically used to measure the resistance of a simple earthing system Rx.
• The MEC (Main earth conductor) has to be temporarily disconnected.
• To avoid possible risk of electric shock due to voltage difference between Main earth 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.

Notes and safety warnings:

• 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.
• The earth electrode under test must be far enough away from the water pipe to be outside its sphere of influence.
• Therefore, under these circumstances, the reading obtained using the Earth tester will practically indicate the resistance of the simple earthing system Rx under test.
• The MEC (Main earth conductor) has to be temporarily disconnected.
• 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.