AEMC 4500 - 4 Operation; Grounding Electrode Resistance

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specically:
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rmlypacked.
Ground Rod
and Clamp
Contact
Resistance
Between Rod
and Soil
Concentric
Shells of
Earth
Figure 4