Method Using 'Dead' Earth - Megger DET2/2 Guia Del Usuario

Measuring Techniques - Testing Earth Electrodes
METHOD USING A 'DEAD' EARTH
The techniques using test spikes explained earlier are
the preferred methods of earth testing. In congested
areas it may not be possible to find suitable sites for the
test spikes, nor sufficient space to run the test leads. In
such cases a low resistance conductive water main
may be available. This is referred to as a 'dead' earth.
Great care must be taken before deciding to adopt this
method and its use is not to be encouraged. Before
employing this method, the user must be quite sure that
no part of the 'dead' earth installation contains plastic or
other non-metallic materials.
1) Short together terminals 'P1' and 'C1'.
2) Short together terminals 'P2' and 'C2'.
2) Firmly connect a test lead to 'C1' and 'P1' and the
other test lead to 'P2' and 'C2'.
3) Firmly connect the free ends of the test leads
to the 'dead' earth, and to the electrode under test.
4) Press the Test push, and take a reading in
the normal way.
This test will give give the combined resistance to earth
of the two earths in series. If that of the 'dead' earth is
negligible then the reading may be taken as that of the
electrode under test .
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The resistance of the two test leads can be found by
firmly joining their free ends together, pressing the Test
push and taking the reading in the usual way. Test lead
resistance can then be subtracted from the original
reading, to obtain the combined resistance of the earth
electrode and the 'dead' earth.
In congested urban areas, the Star-Delta method is the
preferable. This method is explained along with other
methods referred to, in 'Getting Down to Earth' (see
'Accessories' - Publications).
'Dead' earth testing
E
Electrode
under test