AEMC 4500 - Maintenance and Support; Power Supply and Battery Management

36 Digital Ground Resistance Tester Model 4500
4.10 Multiple Electrode System
A single driven ground electrode is an economical and simple means of
making a good ground system. But sometimes a single rod will not provide
sufcientlowresistance,andseveralgroundelectrodeswillbedrivenand
connectedinparallelbyacable.Veryoftenwhentwo,threeorfourground
electrodes are used, they are driven in a straight line; when four or more
areused,ahollowsquarecongurationisusedandthegroundelectrodes
arestillconnectedinparallelandequallyspaced(Figure21).
In multiple electrode systems, the 62% method electrode spacing may no
longerbeapplieddirectly.Thedistanceoftheauxiliaryelectrodesisnow
basedonthemaximumgriddistance(e.g.inasquare,thediagonal;ina
line,thetotallength.Forexample,asquarehavingasideof20ftwillhave
adiagonalofapproximately28ft).
DIAGONAL
DIAGONAL
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Figure 21