AEMC 4500 - Position of Auxiliary Electrodes in Measurements

Digital Ground Resistance Tester Model 4500 25
ZYX
VOLTMETER (E)
AUXILIARY
POTENTIAL
ELECTRODE
GROUND
ELECTRODE
UNDER TEST
AUXILIARY
CURRENT
ELECTRODE
AMMETER (I)
CURRENT
SUPPLY
R
EARTH
Figure 9
NOTE: Terminals X and Xv are shorted together in three-point measure-
ment.
4.3.1 Position of the Auxiliary Electrodes in Measurements
The goal in precisely measuring the resistance to ground is to place the
auxiliarycurrentelectrodeZfarenoughfromthegroundelectrodeunder
testsothattheauxiliarypotentialelectrodeYwillbeoutsideoftheeffec-
tiveresistanceareasofboththegroundelectrodeandtheauxiliarycurrent
electrode.ThebestwaytondoutiftheauxiliarypotentialrodYisoutside
the effective resistance areas is to move it between X and Z and to take
areadingateachlocation.IftheauxiliarypotentialrodYisinaneffective
resistancearea(orinbothiftheyoverlap),bydisplacingit,thereadings
takenwillvarynoticeablyinvalue.Undertheseconditions,noexactvalue
for the resistance to ground may be determined.