Testing soil resistivity is a fundamental part of earth system design, providing the raw data on which the design is based. Factors affecting soil resistivity include soil composition, temperature and moisture content, which can vary with the seasons.

Periodic checking of the soil is necessary to ensure that seasonal variations are within the design parameters of the system.

The classic methods of testing electrode resistance based on fall of potential are used both at installation time and also for periodic checking the condition of the electrodes.

Unfortunately soils that have low resistivity are often corrosive to electrodes, making regular checking important.

All the new family of Megger earth testers allow the use to perform this test and include stake and wire kits as standard.

Testing earth electrodes in existing installations using standard three pole methods normally involves the disconnection of the electrode under test to avoid the influence of parallel paths.

These parallel paths are created by the earthing system of the installation or by other earth electrodes forming the earth system.

Using the Megger DET3TC earth tester with the ICLAMP allows the user to measure the individual earth electrode resistance, using traditional fall of potential methods, but without disconnection of the electrode under test.

Use where the resistance between a conducting part, such as building steelwork and the earth electrode needs to be measured, or where site conditions means that test stakes are impractical.

This test is performed using the same A.C. source as the 3 pole test method and as such may not be suitable for bonding checks as specified by local regulations.

All of the new Megger earth testers can perform this test and unlike some instruments, no external linking on the instrument is required.

This technique is suitable for connected earth electrodes and lighting systems as it relies on an existing complete circuit with the soil to take its measurement.

No disconnection is required, the DET10C or DET20C is simply placed around the conductor where they generate the signal in the circuit using magnetic induction and then calculates the resistance.

They have the added benefit of being able to measure earth current. Care is needed in the application of these instruments to ensure that the circuit under test is valid.

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