AEMC 3620 User manual

GROUND RESISTANCE
TESTER
ENGLISH User Manual
3620
!
ZYX
C1 P2 C2
INSTRUMENTS
Ω
Press To
Measure
X-Z Fault
X-Y Hi Resistance
X-Y Hi Noise
GROUND RESISTANCE TESTER
MODEL 3620
REFER TO USER MANUAL
FOR FAULT WARNING LIGHT
EXPLANATIONS
0.5
25
1k
®

Statement of Compliance
Chauvin Arnoux®, Inc. d.b.a. AEMC®Instruments
certifies that this instrument has been calibrated
using standards and instruments traceable to
international standards.
We guarantee that at the time of shipping your
instrument has met its published specifications.
An NIST traceable certificate may be
requested at the time of purchase, or obtained
by returning the instrument to our repair and
calibration facility, for a nominal charge.
The recommended calibration interval for this
instrument is 12 months and begins on the date of
receipt by the customer. For recalibration, please
use our calibration services. Refer to our repair
and calibration section at www.aemc.com.
Serial #: ______________________________
Catalog #: ______________________________
Model #: 3620
Please fill in the appropriate date as indicated:
Date Received: _________________________________
Date Calibration Due: _______________________
Chauvin Arnoux®, Inc.
d.b.a AEMC®Instruments
www.aemc.com

Table of Contents
1. INTRODUCTION............................................................................... 3
1.1 International Electrical Symbols................................................4
1.2 DenitionofMeasurementCategories .....................................4
1.3 ReceivingYourShipment..........................................................4
1.4 OrderingInformation.................................................................5
1.4.1 Kits,AccessoriesandReplacementParts ....................5
2. PRODUCT FEATURES ...................................................................... 6
2.1 ControlFeatures .......................................................................6
2.2 FaultIndicatorLEDs .................................................................7
2.2.1 X-ZFault .......................................................................7
2.2.2 X-YHighResistance.....................................................7
2.2.3 X-YHighNoise .............................................................7
2.3 FaultIndicatorTipsAndSolutions ............................................8
3. SPECIFICATIONS............................................................................. 9
3.1 Electrical ...................................................................................9
3.2 Mechanical................................................................................9
3.3 Environmental.........................................................................10
3.4 SafetySpecications ..............................................................10
4. OPERATION .................................................................................. 11
4.1 GroundResistanceValues ..................................................... 11
4.2 GroundResistanceTestingPrinciple.....................................13
4.2.1 PositionoftheAuxiliaryElectrodesinMeasurements 14
4.3 MeasuringResistanceofGroundElectrodes (62%Method)..15
4.3.1 AuxiliaryElectrodeSpacing ........................................17
4.4 GroundResistanceMeasurementProcedure (3-Point)..........18
4.5 2-PointMeasurement (SimpliedMeasurement) ...................19
4.6 ContinuityMeasurement.........................................................20
4.7 HowtoUse25WCalibrationChecker.....................................20

5. MAINTENANCE ............................................................................. 21
5.1 Warning...................................................................................21
5.2 Cleaning..................................................................................21
5.3 ReplacingtheBattery .............................................................21
5.4 ReplacingtheSafetyFuse......................................................22
RepairandCalibration...........................................................................23
TechnicalandSalesAssistance ............................................................23
LimitedWarranty ...................................................................................24
WarrantyRepairs...................................................................................24

Ground Resistance Tester Model 3620 3
CHAPTER 1
INTRODUCTION
WARNING
“It should be impressed on all personnel that a lethal potential can exist
between the station ground and a remote ground if a system fault involving
the station ground occurs while tests are being made. Since one of the
objects of tests on a station ground is the establishment of the location of
an effectively remote point for both current and potential electrodes, the
leads to the electrodes must be treated as though a possible potential
could exist between these test leads and any point on the station ground
grid.”
- excerpted from IEEE Std. 81-1962
Thesesafetywarningsareprovidedtoensurethesafetyofper-
sonnelandproperoperationoftheinstrument.
• The instrument must not be operated beyond its specied
operatingrange.
• Safetyistheresponsibilityoftheoperator.
• Allmetalobjectsorwiresconnectedtotheelectricalsystem
shouldbeassumedtobelethaluntiltested.Groundingsys-
temsarenoexception.
• Useextremecautionwhenusingtheinstrumentaroundener-
gizedelectricalequipment.
• Neverattempttousetheinstrumenttotwistorprytheground
electrode or ground wire away from the equipment being
grounded.
• AEMC®Instrumentsconsiderstheuseofrubberglovestobe
anexcellentsafetypracticeeveniftheequipmentisproperly
operatedandcorrectlygrounded.
• Alwaysinspecttheinstrumentandleadspriortouse.Replace
anydefectivepartsimmediately.

4 Ground Resistance Tester Model 3620
1.1 International Electrical Symbols
This symbol signifies that the instrument is protected by double or rein-
forced insulation.
This symbol on the instrument indicates a WARNING and that the operator
must refer to the user manual for instructions before operating the
instrument. In this manual, the symbol preceding instructions indicates that
if the instructions are not followed, bodily injury, installation/sample and
product damage may result.
Risk of electric shock. The voltage at the parts marked with this symbol may
be dangerous.
In conformity with WEEE 2002/96/EC
1.2 Definition of Measurement Categories
Cat. I: Formeasurements oncircuits notdirectlyconnectedtotheAC
supply wall outlet such as protected secondaries, signal level,
andlimitedenergycircuits.
Cat. II: For measurements performed on circuits directly connected to
the electrical distribution system. Examples are measurements
onhouseholdappliancesorportabletools.
Cat. III: For measurements performed in the building installation at
the distribution level such as on hardwired equipment in xed
installationandcircuitbreakers.
Cat. IV: For measurements performed at the primary electrical supply
(<1000V) such as on primary overcurrent protection devices,
ripplecontrolunits,ormeters.
1.3 Receiving Your Shipment
Uponreceivingyourshipment,makesurethatthecontentsareconsistent
withthepackinglist.Notifyyourdistributorofanymissingitems.Iftheequip-
mentappearstobedamaged,leaclaimimmediatelywiththecarrierand
notifyyourdistributoratonce,givingadetaileddescriptionofanydamage.
Savethedamagedpackingcontainertosubstantiateyourclaim.

Ground Resistance Tester Model 3620 5
1.4 Ordering Information
Ground Resistance Tester Model 3620............................ Cat. #2114.90
Includes soft carrying case, batteries and a user manual.
Ground Resistance Tester Model 3620 Kit (150 ft) ......... Cat. #2135.10
Includes ground tester, two 150 ft color-coded leads on spools (red/blue), one 30 ft lead
(green), two T-shaped auxiliary ground electrodes, set of 5 spaded lugs, one 100 ft AEMC®
tape measure, batteries, carrying bag, user manual and warranty card.
Ground Resistance Tester Model 3620 Kit (300 ft) ......... Cat. #2135.11
Includes ground tester, two 300 ft color-coded leads on spools (red/blue), two 100 ft color-
coded leads (hand tied-green/black), four T-shaped auxiliary ground electrodes, set of 5
spaded lugs, one 100 ft AEMC®tape measure, batteries, carrying bag, user manual and
warranty card.
Ground Resistance Tester Model 3620 Kit (500 ft) ......... Cat. #2135.11
Includes ground tester, two 500 ft color-coded leads on spools (red/blue), two 100 ft color-
coded leads (hand tied-green/black), one 30 ft lead (green), four T-shaped auxiliary ground
electrodes, set of 5 spaded lugs, one 100 ft AEMC®tape measure, batteries, carrying bag,
user manual and warranty card.
1.4.1 Kits, Accessories and Replacement Parts
Test Kit for 3-Point Testing (150 ft) .................................. Cat. #2135.35
Includes two 150 ft color-coded leads on spools (red/blue), one 30 ft lead (green), two T-
shaped auxiliary ground electrodes, set of 5 spaded lugs, one 100 ft AEMC®tape measure,
carrying bag.
Test Kit for 4-Point Testing (300 ft) .................................. Cat. #2135.36
Includes two 300 ft color-coded leads on spools (red/blue), two 100 ft color-coded leads
(hand-tied, green/black), four T-shaped auxiliary ground electrodes, set of 5 spaded lugs,
one 100 ft AEMC®tape measure, carrying bag.
Test Kit for 4-Point Testing (500 ft) .................................. Cat. #2135.37
Includes two 500 ft color-coded leads on spools (red/blue), two 100 ft color-coded leads
(hand-tied, green/black), one 30 ft lead (green), four T-shaped auxiliary ground electrodes,
set of 5 spaded lugs, one 100 ft AEMC®tape measure, carrying bag.
Test Kit for 3-Point Testing (Supplementalfor4-PointTesting)... Cat. #2135.38
Includes two 100 ft color-coded leads (hand-tied, green/black), one 30 ft lead (green), two
T-shaped auxiliary ground electrodes, set of 5 spaded lugs, one 100 ft AEMC®tape measure,
carrying bag.
25W Calibration Checker................................................... Cat. #2130.59
Tape Measure – AEMC 100 ft ............................................ Cat. #2130.60
Ground Tester Video/Workbook Set ................................ Cat. #2130.64
Set of 2, T-Shaped Auxiliary Ground Electrodes............ Cat. #2135.39
Fuse – Set of 5, 0.1A, >250V, 0.25 x 1.25"........................ Cat. #2970.12

6 Ground Resistance Tester Model 3620
CHAPTER 2
PRODUCT FEATURES
2.1 Control Features
!
ZYX
C1 P2 C2
INSTRUMENTS
Ω
Press To
Measure
X-Z Fault
X-Y Hi Resistance
X-Y Hi Noise
GROUND RESISTANCE TESTER
MODEL 3620
REFER TO USER MANUAL
FOR FAULT WARNING LIGHT
EXPLANATIONS
0.5
25
1k
®
243 5 1
6
7
8
9
1011
Figure 1
1. Press-to-measurebutton 7. Zeroadjustmentscrew
2. InputterminalX(C1) 8. Lowbatteryindicator
3. InputterminalY(P2) 9. X-Yhinoiseindicator
4. Shortinglink 10. X-Yhiresistanceindicator
5. InputterminalZ(C2) 11. X-Zfaultindicator
6. Display

Ground Resistance Tester Model 3620 7
2.2 Fault Indicator LEDs
ThethreeLEDindicatorsdescribedbelowconrmthecorrectmeasure-
mentbeingtakenifnoneofthemarelit.
2.2.1 X-Z Fault
ThisLEDsignalsthatthevoltagebetweenterminalsXandZexceeds30V
peak.
Therearevepossiblecauses:
• theresistanceofthecurrentcircuitbetweenXandZistoohigh
• interferencevoltageinthecurrentcircuitistoohigh
• thefuseisblown
• thecircuitisopen(leadnotconnected)
• whenthereadingisunder0.5W(needleontheleftofthescale)
NOTE: When performing a test this light will initially come on for approxi-
mately three seconds until the nominal test voltage is reached and then the
light will go out if all indications are normal.
2.2.2 X-Y High Resistance
ThisLEDsignalsthattheresistanceinthevoltagecircuit(betweenXand
Y)istoohigh(approximately50kW)orthatthecircuitmaybeopen.
Flashingwillcontinuethroughoutthemeasurement,eveniftheresistance
drops below the threshold; for example, after reconnecting or lowering
auxiliaryrodresistance.
Inthiscase,youmustreleasethepush-buttonandpressagainafterthe
faulthasbeencorrected.
Occasionally,astrayvoltageabove6VDCmayalsosetoffthislight.Check
theleadsforapossiblesolution.
2.2.3 X-Y High Noise
This LED signals the presence of excessive noise (approximately 13V
peak)inthevoltagecircuit(betweenXandY).
Oneremedyistouseshieldedleadsfromtheinstrumenttotheauxiliary
electrodes.Connectalltheshieldstotherodundertest.

8 Ground Resistance Tester Model 3620
Galvanometer Pointer
• Ifthepointerstopsontherightside,thisindicatesthatyoumea-
suredmorethan1000W(over-rangingcondition)orthatthecircuit
isopen.
• Ifthepointerstopsontheleftside,thisindicatesthatyoumea-
sured less than 0.5W. This may also indicate that the X andY
rods,ortheXandZrods,wereinverted.
• Checktheconnections.
2.3 Fault Indicator Tips And Solutions
TheLEDindicatorsshowexcessiveelectroderesistanceand/orexcessive
transientnoiseand/orstraycurrent.
In the event of an incorrect measurement indication:
• Improvethequalityoftheconnectiontoearthofauxiliaryground
electrodesYandZ.Zisthemostlikelysourceofproblemscaused
byexcessiveelectroderesistance.
• Checkconnectionsforcontinuitybetweenleadsandelectrodes.
• Be sure that electrodes are properly inserted; they should be
buriedasmuchaspossible.
• Ifhighelectroderesistancestillexistsafterproperlyinsertingaux-
iliaryelectrodes intotheearth,trypouring wateronandaround
theauxiliaryelectrodes.Thiswillimprovetheirelectricalconnec-
tiontoearth.
• Ifstraycurrentsaresuspected,onesolutiontoreducetheirinu-
enceistomovebothYandZelectrodesinanarcrelativetotheX
electrode(try,e.g.,a90°shift),andtestagain.
NOTE: Accuracy may be affected by auxiliary ground rod (Ry, Rz) resistance
levels and by stray signal levels (earth currents).

Ground Resistance Tester Model 3620 9
CHAPTER 3
SPECIFICATIONS
3.1 Electrical
Measurement Range: 0.5 to 1000W
Test Current: 10mA
Operating Frequency: 128Hzsquarewave
Accuracy*:5%ofReading±0.1%ofgalvanometerscalelength
Auxiliary Electrode Inuence:
Rz:3000timesthereadingupto50kW
Ry:50kW
Voltage Withstand:
Unitisfuseprotected.Intheeventofasystemfault,theunitscanwith-
stand250Vrmswithspikesof3000VACor1000VDC.
Power Source:
Eight1.5V“AA”batteries;Alkalinerecommended
Battery Life:168015-secondmeasurements(approx)
Low Battery Indicator:Ifthe“LowBattery”indicatorlightsup,the
batteriesarelosingpower.Theavailableoperatingtimeremainingis80
15-secondmeasurements(approx)
Fuse Protection:Highbreakingcapacity0.1A,>250V,0.25x1.25"
*Accuracies and specications are given for an ambient temperature of 23°C ± 3K, RH of 45
to 55%, battery power at 8V, auxiliary resistance at the measurement terminals <200W, no
stray voltage and a magnetic eld from 0 to 40A/m.
3.2 Mechanical
Dimensions:8.7x5.4x5.9"(220x136x150mm)
Weight: 2.9lbs(1.3kg)

10 Ground Resistance Tester Model 3620
Connection: Color-codedterminalsacceptspadelugswithminimumgap
of6mmorstandard4mmbananajacks
Meter Movement: Pivotmovement
Scale: 3.1"(77mm)whitescalewithblackpointer
Case: Heavy-duty,ABS
Colors: Case-safetyyellow;Frontpanel-gray
Mechanical Shock: IEC 68-2-27
Vibration: IEC 68-2-6
Drop Test: IEC 68-2-32
Case Material: UL94
Environmental: O-ringsealedagainstdustandwatertoIP50
3.3 Environmental
Operating Temperature:14°to131°F(-10°to55°C)
Storage Temperature:-40°to158°F(-40°to70°C);
 0to90%RHwithbatteriesremoved
Relative Humidity:20to90%maximum
3.4 Safety Specifications
Electrical:EN61010-1CatlII,Pollutiondegree2,24V
Electromagnetic Compatibility: Emission: EN 50081-1
Immunity: EN 50082-1
*All specications are subject to change without notice

Ground Resistance Tester Model 3620 11
CHAPTER 4
OPERATION
4.1 Ground Resistance Values
NEC®2008article250.56regardingtheresistanceofrod,pipeandplate
electrodesstatesthatiftherod,pipe,orplatedoesnothavearesistance
of25Ωorlesstogroundshallbeaugmentedbyoneadditionalelectrodeof
anyofthetypesspeciedby250.52(A)(4)through(A)(8).Wheremultiple
rod,pipeorplateelectrodesareinstalledtomeettherequirementsofthe
section,theyshallnotbelessthan6feetapart.
FPN:Theparallelingefciencyofrodslongerthan8feetisimprovedby
spacinggreaterthan6feetapart.
TheNationalElectricalCode®(NEC®)statesthattheresistancetoground
shall not exceed 25W. This is an upper limit and guideline, since much
lowerresistanceisrequiredinmanyinstances.
“How low in resistance should a ground be?”
An arbitrary answer to this in ohms is difcult. The lower the ground
resistance, the safer, and for positive protection of personnel and
equipment,itisworththeefforttoaimforlessthanoneohm.Itisgenerally
impracticaltoreachsuchalowresistancealongadistributionsystemor
atransmissionlineorinsmallsubstations.Insomeregions,resistances
of5Worlessmaybeobtainedwithoutmuchtrouble.Inothers,itmaybe
difculttobringresistanceofdrivengroundsbelow100W.
Acceptedindustrystandardsstipulatethattransmissionsubstationsshould
bedesignednottoexceedoneohmresistance.Indistributionsubstations,
themaximumrecommendedresistanceis5W.Inmostcases,theburied
gridsystemofanysubstationwillprovidethedesiredresistance.
Inlightindustrialorintelecommunicationscentralofces,5Wisoftenthe
acceptedvalue.Forlightningprotection,thearrestersshouldbecoupled
withamaximumgroundresistanceof1W.
Theseparameterscanusuallybemetwiththeproperapplicationofbasic
groundingtheory.Therewillalwaysexistcircumstanceswhichwillmake
it difcult to obtain the ground resistance required by the NEC®. When

12 Ground Resistance Tester Model 3620
thesesituationsdevelop,severalmethods ofloweringthe groundresis-
tancecanbeemployed.Theseincludeparallelrodsystems,deepdriven
rod systems utilizing sectional rods and chemical treatment of the soil.
Additionalmethods,discussedinotherpublisheddata,areburiedplates,
buried conductors (counterpoise), electrically connected building steel,
andelectricallyconnectedconcretereinforcedsteel.
Electricallyconnectingtoexistingwaterandgasdistributionsystemswas
oftenconsideredtoyieldlowgroundresistance;however,recentdesign
changesutilizingnon-metallicpipesandinsulatingjointshavemadethis
methodofobtaininga low resistance ground questionableandinmany
instancesunreliable.
Groundrods,ofcourse,willberequiredinhighvoltagetransmissionlines,
wheremaximumresistanceof15ohmsisrecommended;andindistribu-
tionlines,wheremaximumresistanceof25ohmsispreferred.Allelectri-
calsystemsconstructedinaccordancewiththeNationalElectricalCode®,
shouldnotexceed25ohms.
Themeasurementofgroundresistancesmayonlybeaccomplishedwith
speciallydesignedtestequipment.MostinstrumentsusetheFallofPoten-
tial principle of alternating current (AC) circulating between an auxiliary
electrodeandthegroundelectrodeundertest;thereadingwillbegiven
inohmsandrepresentstheresistanceofthegroundelectrodetothesur-
roundingearth.AEMC®Instrumentshasalsorecentlyintroducedaclamp-
ongroundresistancetester.
Note: The National Electrical Code®and NEC®are registered trademarks of the National Fire
Protection Association.

Ground Resistance Tester Model 3620 13
4.2 Ground Resistance Testing Principle
(Fall-of-Potential — 3-Point Measurement)
Three-point measurement is used to measure resistance to ground of
groundrodsandgrids.ThepotentialdifferencebetweenrodsXandYis
measuredbyavoltmeter,andthecurrentowbetweenrodsXandZis
measuredbyanammeter.
By Ohm’s Law E = RI or R = E/I, we may obtain the ground electrode
resistance R.
IfE=20VandI=1A,then:
R===20ohms
E
I
20
1
Itisnotnecessarytocarryoutallthemeasurementswhenusingaground
tester.Thegroundtesterwillmeasuredirectlybygeneratingitsowncur-
rentanddisplayingtheresistanceofthegroundelectrode.
ZYX
VOLTMETER (E)
AUXILIARY
POTENTIAL
ELECTRODE
GROUND
ELECTRODE
UNDER TEST
AUXILIARY
CURRENT
ELECTRODE
AMMETER (I)
CURRENT
SUPPLY
R
EARTH
Figure 2
NOTE: Terminals X and Xv are shorted together in three-point measurement.

14 Ground Resistance Tester Model 3620
4.2.1 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.
100% of Distance
Between X & Z
Resistance
Reading Variation
Effective Resistance
Areas (Overlapping)
XY'YY'' Z
Figure 3
On the other hand, if the auxiliary potential rod Y is located outside of
theeffectiveresistanceareas,asYismovedbackandforththereading
variationisminimal.Thereadingstakenshouldberelativelyclosetoeach
other,andarethebestvaluesfortheresistancetogroundofthegroundX.
Thereadingsshouldbeplottedtoensurethattheylieina“plateau”region
asshowninFigure4.
100% of Distance
Between X & Z
Resistance
Reading Variation
Effective Resistance
Areas (No Overlap)
XY'YY'' Z
Figure 4

Ground Resistance Tester Model 3620 15
4.3 Measuring Resistance of Ground Electrodes
(62% Method)
The62%methodhasbeenadoptedaftergraphicalconsiderationandafter
actualtest.Itisthemostaccuratemethodbutislimitedbythefactthat
thegroundtestedisasingleunit.Thismethodappliesonlywhenallthree
electrodesareinastraightlineandthegroundisasingleelectrode,pipe,
orplate,etc.,asinFigure5.
Alligator Clips
Ground Rod
Y Electrode Z Electrode
Ground
Strip
ZYX
C1 P2 C2
INSTRUMENTS
!
Ω
Press To
Measure
X-Z Fault
X-Y Hi Resistance
X-Y Hi Noise
GROUND RESISTANCE TESTER
MODEL 3620
REFER TO USER MANUAL
FOR FAULT WARNING LIGHT
EXPLANATIONS
0.5
25
1k
Figure 5
ConsiderFigure6,whichshowstheeffectiveresistanceareas(concentric
shells)ofthegroundelectrodeXandoftheauxiliarycurrentelectrodeZ.
Theresistanceareasoverlap.Ifreadingsweretakenbymovingtheauxiliary
potentialelectrodeYtowardseitherXorZ,thereadingdifferentialswould
be great and one could not obtain a reading within a reasonable band
oftolerance.Thesensitiveareasoverlapandactconstantlytoincrease
resistanceasYismovedawayfromX.

16 Ground Resistance Tester Model 3620
Distance from Y to Ground Electrode
Resistance
Overlapping Effective
Resistance Areas
XYZ
Ground
Electrode
Under Test
Auxiliary
Potential
Electrode
Auxiliary
Current
Electrode
Figure 6
Now consider Figure 7, where the X and Z electrodes are sufciently
spacedsothattheareasofeffectiveresistancedonotoverlap.Ifweplot
theresistance,measuredwendthatthemeasurementsleveloffwhen
Yisplacedat62%ofthedistancefromXtoZ,andthatthereadingson
eithersideoftheinitialYsettingaremostlikelytobewithintheestablished
toleranceband.Thistolerancebandisdenedbytheuserandexpressed
asapercentoftheinitialreading:±2%,±5%,±10%,etc.
Resistance
Distance from Y to Ground Electrode
Effective
Resistance
Areas Do
Not Overlap
XYZ
Ground
Electrode
Under Test
Auxiliary
Potential
Electrode
Auxiliary
Current
Electrode
D
62% of D 38% of D
Resistance of
Auxiliary Current
Electrode
Resistance of Earth Electrode
Figure 7

Ground Resistance Tester Model 3620 17
4.3.1 Auxiliary Electrode Spacing
NodenitedistancebetweenXandZcanbegiven,sincethisdistanceis
relativetothediameteroftheelectrodetested,itslength,thehomogeneity
of the soil tested, and particularly, the effective resistance areas. How-
ever,anapproximatedistancemaybedeterminedfromthefollowingchart
whichisgivenforahomogeneoussoilandanelectrodeof1"indiameter.
(Foradiameterof1/2",reducethedistanceby10%;foradiameterof2”
increasethedistanceby10%.)
Depth Driven Distance to Y Distance to Z
6 ft 45 ft 72 ft
8 ft 50 ft 80 ft
10 ft 55 ft 88 ft
12 ft 60 ft 96 ft
18 ft 71 ft 115 ft
20 ft 74 ft 120 ft
30 ft 86 ft 140 ft
Approximate Distance to Auxiliary Electrodes
Using the 62% Method

18 Ground Resistance Tester Model 3620
4.4 Ground Resistance Measurement Procedure
(3-Point)
WARNING: Use extreme caution when disconnecting the ground connection
from the rest of the circuit. Current may be flowing and a dangerous potential
could exist between the disconnected wires.
Procedure
• DisconnectshortinglinkbetweenYandZ(C2,P2)
• ConnectXtothegroundrodtobetested
• ConnectY(P2)tothecentralelectrode
• ConnectZ(C2)totheouterelectrode
• Depressthe“Measure”buttontomeasuregroundresistance
NOTE: When performing a test this light will initially come on for approxi-
mately three seconds until the nominal test voltage is reached and then the
light will go out if all indications are normal.
ZYX
C1 P2 C2
INSTRUMENTS
!
Ω
Press To
Measure
X-Z Fault
X-Y Hi Resistance
X-Y Hi Noise
GROUND RESISTANCE TESTER
MODEL 3620
REFER TO USER MANUAL
FOR FAULT WARNING LIGHT
EXPLANATIONS
0.5
25
10
1k
Alligator Clips
YZX
52% 62% 72%
0% 100% of distance
between X and Z
Ground Rod Y Electrode Z Electrode
Ground Rod
Y Electrode Z Electrode
Ground
Strip
-10% 3rd
Measurement +10% 2nd
Measurement
®
Figure 8