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Grounding Electrode Resistance
Figure 8 illustrates a grounding rod. The resistance of the electrode has
the following components:
A)
the resistance of the metal and that of the connection to it
B)
the contact resistance of the surrounding earth to the electrode
C)
the resistance in the surrounding earth
More specifically:
A) Grounding electrodes are usually made of a very conductive
metal (copper) with adequate cross sections so that overall resis-
tance is negligible.
B) The National Bureau of Standards has demonstrated that the
resistance between the electrode and the surrounding earth is negli-
gible if the electrode is free of paint, grease or other coating, and if
the earth is firmly packed.
Figure 8
16
Ground Rod
Ground Rod
and Clamp
and Clamp
Contact
Contact
Resistance
Resistance
Between Rod
Between Rod
and soil
and Soil
Concentric
Concentric
Shells of
Shells of
Earth
Earth
Digital Ground Resistance Tester Model 4500
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