Digital Ground Resistance Tester Model 4500
15
CHAPTER 4
OPERATION
4.1
Grounding Electrode Resistance
Figure 4 illustrates a grounding rod. The resistance of the electrode has
the following components:
• the resistance of the metal and that of the connection to it
• the contact resistance of the surrounding earth to the electrode
• 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 resistance is
negligible.
B) The National Institute of Standard and Technology (N.I.S.T.) has
demonstrated that the resistance between the electrode and the
surrounding earth is negligible if the electrode is free of paint,
grease or other coating, and if the earth is firmly packed.
Ground Rod
and Clamp
Contact
Resistance
Between Rod
and Soil
Concentric
Shells of
Earth
Figure 4
