Megger DET2/2, User Manual

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The installation of satisfactory earthing systems is an
essential part of electricity supply, wiring safety and
installation economics. It is also of great importance in
many communications systems.
The primary application of the DET2/2 is in the testing
of earth electrodes, whether these take the form of a
single electrode, multiple electrodes, mesh systems,
earth plates or earth strips. All earthing arrangements
should be tested immediately after installation and at
periodic intervals thereafter.
Choice of electrode site
For an earth electrode system to perform satisfactorily
it must always have a low total resistance to earth. This
value will be influenced by the specific resistance of
the surrounding soil. This in turn depends on the
nature of the soil and its moisture content. Before
sinking an electrode or electrode system it is often
helpful to survey the surrounding area before choosing
the final position for the electrode. It is possible with
DET2/2 to obtain the resistivity of the soil over an area
and at different levels beneath the surface of the
ground. These resistivity surveys may show whether
any advantage is to be gained by driving electrodes to
a greater depth, rather than increasing the cost by
having to add further electrodes and associated cables,
in order to obtain a specified total earth system
resistance.
Earthing Systems Maintenance
After installation, checks may be made on an earthing
system to see if there is any significant change in the
resistance over a period of time or under different soil
moisture conditions, (e.g. brought about by changing
weather conditions or different seasons of the year).
Such checks will indicate if the earth electrode
resistance to earth has been exceeded by changing
soil conditions or ageing of the system.
Other Applications
For archaeological and geological purposes, an
investigation of soil structure and building remains can
be carried out at varying measured depths, by the
resistivity survey technique.
In all cases the accuracy of the instrument readings
may be taken to be higher than the changes caused by
natural variables in soil characteristics.
A further application is in continuity testing, for example
checking the resistance of conductors used in an
earthing circuit.
Applications
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