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Digital Ground Resistance TesterModel 3640

CHAUVIN ARNOUX GROUP

®

www.aemc.com

ENGLISHUser Manual

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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 #: 3640

Please fill in the appropriate date as indicated:

Date Received: _________________________________

Date Calibration Due: _______________________

Chauvin Arnoux®, Inc.d.b.a AEMC® Instrumentswww.aemc.com

2 Digital Ground Resistance Tester Model 3640

Table of Contents

1. INTRODUCTION ............................................................................... 41.1 International Electrical Symbols ................................................41.2 DefinitionofMeasurementCategories .....................................51.3 ReceivingYourShipment ..........................................................51.4 OrderingInformation .................................................................5

1.4.1 Kits,AccessoriesandReplacementParts ....................6

2. PRODUCT FEATURES ...................................................................... 72.1 3640ControlandConnectorIdentification ...............................72.2 FaultIndicatorLEDs .................................................................8

2.2.1 X-ZFault .......................................................................82.2.2 X-YHighResistance ........................................................82.2.3 X-YHighNoise ...........................................................8

2.3 Over-rangeIndication ...............................................................92.4 FaultLEDIndication–TipsandSolutions ................................92.5 DisplayofaNegativeMeasurement .........................................9

3. SPECIFICATIONS........................................................................... 103.1 Electrical .................................................................................103.2 Mechanical ..............................................................................113.3 Environmental .........................................................................113.4 SafetySpecifications ..............................................................113.5 Auto-ranging ...........................................................................12

4. OPERATION .................................................................................. 134.1 GroundingElectrodeResistance ............................................13

4.1.1 EffectofGroundElectrodeSizeandDepthon Resistance ..................................................................154.1.2 EffectsofSoilResistivityonGroundElectrode Resistance ..................................................................164.1.3 FactorsAffectingSoilResistivity .................................164.1.4 EffectofGroundRodDepthonResistance ................19

4.2 GroundResistanceValues .....................................................204.3 GroundResistanceTestingPrinciple .....................................22

Digital Ground Resistance Tester Model 3640 3

4.3.1 PositionofAuxiliaryElectrodesinMeasurements ......234.4 MeasuringResistanceofGroundElectrodes .........................24

4.4.1 AuxiliaryElectrodeSpacing ........................................254.5 GroundResistanceMeasurementProcedure ........................264.6 MultipleElectrodeSystem ......................................................274.7 2-PointMeasurement(SimplifiedMeasurement) ...................294.8 ContinuityMeasurement .........................................................304.9 How to Use 25ΩCalibrationChecker .....................................31

5. MAINTENANCE ............................................................................. 325.1 Warning...................................................................................325.2 Cleaning ..................................................................................325.3 ReplacingtheBattery .............................................................325.4 ReplacingtheSafetyFuse ......................................................33

RepairandCalibration ...........................................................................34

TechnicalandSalesAssistance ............................................................34

Limited Warranty ...................................................................................35

WarrantyRepairs ...................................................................................35


CHAPTER 1

INTRODUCTION

WARNING “A lethal voltage can exist between the ground electrode under test and a remote ground during routine conditions or if a power-system fault involving the station ground occurs while ground tests are being conducted. The ground potential rise can be in the order of several thousand volts. Step and touch voltages around the ground electrode under test, test equipment and remote grounds can also be lethal.A test Plan is typically developed and reviewed with applicable test personnel. Appropriate safety rules need to be followed.”

- excerpted from IEEE Std. 81-2012

Thesesafetywarningsareprovidedtoensurethesafetyofpersonnelandproperoperationoftheinstrument.• The instrument must not be operated beyond its specified operatingrange.

• Safetyistheresponsibilityoftheoperator.• Allmetalobjectsorwiresconnectedtotheelectricalsystemshouldbeassumedtobelethaluntiltested.Groundingsystemsarenoexception.

• Use extreme caution when using the instrument around energizedelectricalequipment.

• Neverattempttousetheinstrumenttotwistorprythegroundelectrodeorgroundwireawayfromtheequipmentbeinggrounded.

• The use of rubber gloves is an excellent safety practice even if theequipmentisproperlyoperatedandcorrectlygrounded.

• Always inspect the instrument and leads prior to use. Replace anydefectivepartsimmediately.

1.1 International Electrical SymbolsThis symbol signifies that the instrument is protected by double or reinforced 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 CategoriesCAT II: Formeasurements performed on circuits directly connected to

theelectricaldistributionsystem.Examplesaremeasurementsonhouseholdappliancesorportabletools.

CAT III: For measurements performed in the building installation atthe distribution level such as on hardwired equipment in fixedinstallationandcircuitbreakers.

CAT IV: For measurements performed at the primary electrical supply(<1000V) such as on primary overcurrent protection devices,ripplecontrolunits,ormeters.

1.3 Receiving Your ShipmentUponreceivingyourshipment,makesurethatthecontentsareconsistentwith the packing list. Notify your distributor of anymissing items. If theequipmentappearstobedamaged,fileaclaimimmediatelywiththecar-rierandnotifyyourdistributoratonce,givingadetaileddescriptionofanydamage.Savethedamagedpackingcontainertosubstantiateyourclaim.

1.4 Ordering InformationGround Resistance Tester Model 3640 ............................ Cat. #2114.92Includes soft carrying case, batteries and a user manual.

Ground Resistance Tester Model 3640 Kit (150 ft) .........Cat. #2135.13Includes 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 and user manual.

Ground Resistance Tester Model 3640 Kit (300 ft) .........Cat. #2135.14Includes 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 and user manual.


1.4.1 Kits, Accessories and Replacement Parts

Test Kit for 3-Point Testing ...............................................Cat. #2135.35Includes 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 ...............................................Cat. #2135.36Includes 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 ...............................................Cat. #2135.37Includes 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 (Supplementalfor4-PointTesting) ...Cat. #2135.38Includes 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.

Set of 2, T-Shaped Auxiliary Ground Electrodes ............Cat. #2135.3925Ω Calibration Checker ...................................................Cat. #2130.59Tape Measure – AEMC 100 ft ............................................Cat. #2130.60Fuse - Set of 5, 0.1A, >250V, 0.25 x 1.25" (Fast Blow) ....Cat. #2970.12

Download the Ground Tester Workbook at www.aemc.com

Order Accessories and Replacement Parts Directly OnlineCheck our Storefront at www.aemc.com/store for availability


CHAPTER 2

PRODUCT FEATURES

2.1 3640 Control and Connector Identification

ΩPress ToMeasure

X-Z

X-Y

X-Y

ZYXC1 P2 C2

Fault

Hi Resistance

Hi Noise

GROUND RESISTANCE TESTERMODEL 3640

AUTORANGINGREFER TO USER MANUALFOR FAULT WARNING LIGHTEXPLANATIONS

!

2 3 4 5

6

78910

1

Figure 1

1. Press-to-Measurebutton

2. InputterminalX(C1)

3. InputterminalY(P2)

4. Groundresistanceshortinglink

5. InputterminalZ(C2)

6.Display

7. Low battery indicator

8.X-Yhighnoiseindicator

9.X-Yhighresistanceindicator

10.X-Zfaultindicator


2.2 Fault Indicator LEDsThe three indicators describedbelowconfirm the correctmeasurementbeingtakenifnoneofthemarelit.

2.2.1 X-Z Fault

ThisLEDsignalsthatvoltagebetweenterminalsXandZexceeds30Vpeak.

Therearefourpossiblecauses:• theresistanceofthecurrentcircuitbetweenXandZistoohigh• interferencevoltageinthecurrentcircuitistoohigh• thefuseisblown• thecircuitisopen(leadnotconnected)

2.2.2 X-Y High Resistance

ThisLEDsignalsthattheresistanceinthevoltagecircuit(betweenXandY)istoohigh(approx50kΩ)orthatthecircuitmaybeopen.

• Flashingwill continue throughout themeasurement,even if theresistancedropsbelowthethreshold(e.g.afterreconnectingorloweringauxiliaryrodresistance).

• In thiscase,youmustreleasethepush-buttonandpressagainafterthefaulthasbeencorrected.

• Occasionally, a stray voltageabove6VDCmayalso set off thislight.

• Checktheleadsforapossiblesolution.

2.2.3 X-Y High Noise

ThisLEDsignalsthepresenceofexcessivenoise(approx13Vpeak)inthevoltagecircuit(betweenXandY).

• Oneremedyistouseshieldedleadsfromtheinstrumenttotheauxiliaryelectrodes.

• Connectalltheshieldstotherodundertest.


2.3 Over-range IndicationOver-rangeisindicatedwhenthedisplayreads1,orwhenthedisplayisblinkingandtheindicatorislit.

2.4 Fault LED Indication – Tips and SolutionsTheLEDindicatorsshowexcessiveelectroderesistanceandexcessivetransientnoiseand/orstraycurrent.Intheeventofanincorrectmeasurementindication:

• ImprovethequalityoftheconnectiontoearthofauxiliarygroundelectrodesYandZ.Zisthemostlikelysourceofproblemscausedbyexcessiveelectroderesistance.

• Checkconnectionsforcontinuitybetweenleadsandelectrodes.• Be sure that electrodes are properly inserted; they should be

buriedasmuchaspossible.• Ifhighelectroderesistancestillexistsafterproperlyinsertingaux-

iliaryelectrodesintotheearth,trypouringwateronandaroundtheauxiliaryelectrodes.Thiswillimprovetheirelectricalconnec-tiontoearth.

• Ifstraycurrentsaresuspected,onesolutiontoreducetheirinflu-enceistomovebothYandZelectrodesinanarcrelativetotheXelectrode(try,e.g.,a90°shift),andtestagain.

• Displayof0.00:XvandYareshort-circuited.• Displayof<0:XandZrodsarereversed.

NOTE: Accuracy may be affected by auxiliary ground rod (Ry, Rz) resistance levels and by stray signal levels (earth currents).

2.5 Display of a Negative MeasurementDisplay of a negative measurement may be due to reversed polaritybetweengroundrods.Reversepositionsofgroundrods&checkleadsconnection.


CHAPTER 3

SPECIFICATIONS

3.1 ElectricalMeasurement Ranges:Auto-ranging0to2000Ω

Range 20Ω 200Ω 2000ΩMeasurement 0 to 19.99Ω 20 to 199.9Ω 200 to 1999ΩResolution 10mΩ 100mΩ 1ΩTest Current 10mA 1mA 0.1mAAccuracy ± 2% of Reading ± 1ct ± 5% of Reading ± 3ctsOpen Voltage <42V peak

Operating Frequency:128Hzsquarewave

Max. Auxiliary Rod Resistance:Range 20Ω 200Ω 2000ΩCurrent Circuit 3kΩ 30kΩ 50kΩVoltage Circuit 50kΩ

Response Time: Approximately6secondsforastabilizedmeasurement

Interference: Model3640isdesignedtorejecthighlevelsofinterferencevoltage(DC,50/60Hz,harmonics)

• DCvoltageinserieswithX:20V• ACvoltageinserieswithY:13Vpeak• ACvoltageinserieswithZ:32Vpeak

Accuracies and specifications are given for an ambient temperature of 23°C ± 3°, RH of 45 to 55%, battery power at 8V, auxiliary resistance at the measurement terminals <200Ω, no stray voltage and a magnetic field from 0 to 40A/m.

Power Source: Eight1.5V“AA”batteries;Alkalinerecommended.

Battery Life: 180015-secondmeasurements

Low Battery Indicator: Ifthe“LoBat”indicatorlightsup,thebatteriesarelosingpower.Theavailableoperatingtimeremainingis10015-secondmeasurements(approx).

Fuse Protection: High breaking capacity - 0.1A, >250V, 0.25 x 1.25"(FastBlow)


3.2 MechanicalConnection:Color-codedterminalsacceptspadelugswithminimumgapof6mmorstandard4mmbananajacks

Display:7segmentLCD,.71"(18mm)high(3-1/2digit);2000ctsLCDalsoindicatesoverrange,testleadshortsandleadreversals.

Dimensions:8.7x5.4x5.9"(220x136x150mm)

Weight: 2.9lbs(1.3kg)

Case: Heavy-duty,ABS

Colors: Case-safetyyellow;Frontpanel-gray

Mechanical Shock: IEC68-2-27

Vibration: IEC68-2-6

Drop Test: IEC68-2-32

Case Material: UL94

Environmental: O-ringsealedagainstdustandwatertoIP54

3.3 EnvironmentalOperating Temperature: 14°to131°F(-10°to55°C);0to90%RH

Storage Temperature:-40°to158°F(-40°to70°C); 0to90%RHwithbatteriesremoved

3.4 Safety Specifications

Electrical: EN61010-1,CATlII,PollutionDegree2,42V

Electromagnetic Compatibility: Emission:EN61326-1 Immunity:EN61326-1

*Specifications are subject to change without notice.


3.5 Auto-rangingTheselectionofthemeasurementcurrentisdependingontheresistancetomeasure.

WhentheinstrumentisturnedON,themeasurementstartsonthesmallestcurrentrange(100µA).Ifthemeasurementisbetween185and1950cts,therangestaysthesame(100µA).Ifthemeasurementisunder185cts,thecurrentismultipliedby10(within10mAmax).Ifitisabove1950cts,thecurrentisdividedby10(withoutgoingunder100µA).

Thisisdonetoavoidswitchingbackandforthbetweenrangeswhenyouaremeasuring190Ω.Itispossibletodisplay190.0or190Ωdependingontheautomaticrangeselection.


CHAPTER 4

OPERATION

4.1 Grounding Electrode ResistanceFigure3illustratesagroundingrod.Theresistanceoftheelectrodehasthefollowingcomponents:

• theresistanceofthemetalandthatoftheconnectiontoit• thecontactresistanceofthesurroundingearthtotheelectrode• theresistanceinthesurroundingearth

Morespecifically:A) Groundingelectrodesareusuallymadeofaveryconductivemetal

(copper)withadequatecrosssectionssothatoverallresistanceisnegligible.

B) TheNationalInstituteofStandardandTechnology(N.I.S.T.)hasdemonstratedthattheresistancebetweentheelectrodeandthesurrounding earth is negligible if the electrode is free of paint,greaseorothercoating,andiftheearthisfirmlypacked.

Ground Rod

and Clamp

Contact

Resistance

Between Rod

and Soil

Concentric

Shells of

Earth

Figure 3


C) Theonlycomponentremainingistheresistanceofthesurround-ingearth.Theelectrodecanbethoughtofasbeingsurroundedby concentric shells of earth or soil, all of the same thickness.The closer the shell to the electrode, the smaller its surface;hence,thegreateritsresistance.Thefartherawaytheshellsarefromtheelectrode,thegreaterthesurfaceoftheshell;hence,thelowertheresistance.Eventually,addingshellsatadistancefromthegroundingelectrodewillnolongernoticeablyaffecttheoverallearthresistancesurroundingtheelectrode.Thedistanceatwhichthiseffectoccursisreferredtoastheeffectiveresistanceareaandisdirectlydependentonthedepthofthegroundingelectrode.

Intheory,thegroundresistancemaybederivedfromthegeneralformula:

R = ρ Resistance=ResistivityxLA

LengthArea

Thisformulaclearlyillustrateswhytheshellsofconcentricearthdecreaseinresistancethefarthertheyarefromthegroundrod:

R=ResistivityofSoilx ThicknessofShellArea

Inthecaseofgroundresistance,uniformearth(orsoil)resistivitythrough-out thevolume isassumed,although this isseldomthecase innature.The equations for systems of electrodes are very complex and oftenexpressedonlyasapproximations.Themostcommonlyusedformulaforsinglegroundelectrodesystems,developedbyProfessorH.R.DwightoftheMassachusettsInstituteofTechnology,follows:

4Lr

R =ρ

2πLIn -1

R=resistanceinohmsofthegroundrodtotheearth(orsoil)

L=groundingelectrodelength

r=groundingelectroderadius

ρ=averageresistivityinohms-cm


4.1.1 Effect of Ground Electrode Size and Depth on Resistance

Size: Increasing thediameter of the roddoesnotmaterially reduce itsresistance.Doublingthediameterreducesresistancebylessthan10%.

0255075

100

1/2 5/8 3/4 1 1 1/4 1 1/2 1 3/4

Rod Diameter (inches)

Res

ista

nce

in %

Figure 4

Depth: As a ground rod is driven deeper into the earth, its resistanceissubstantiallyreduced.Ingeneral,doublingtherodlengthreducestheresistancebyanadditional40%.

5 15 25 35 40 50 60 70

1

2

3

45

6

8

10

20

30

40

60

80

100

200

Driven Depth in Feet

Ground Resistance Versus Ground Rod Depth

Resis

tance in O

hm

s

1/2" dia.1" dia.

Figure 5

NEC®2014250.52(A)(5)requiresaminimumof8ft(2.4m)oftheelec-trodetobe incontactwith thesoil.Themostcommonofelectrode isa10ft(3m)cylindricalrodwhichmeetstheNEC®code,whichrequiresaminimumdiameterof5/8"(1.59cm).


4.1.2 Effects of Soil Resistivity on Ground Electrode ResistanceDwight’s formula,citedpreviously,showsthat theresistance toearthofgroundingelectrodesdependsnotonlyonthedepthandsurfaceareaofgroundingelectrodesbutonsoilresistivityaswell.Soilresistivity isthekeyfactorthatdetermineswhattheresistanceofagroundingelectrodewillbe,andtowhatdepthitmustbedriventoobtainlowgroundresistance.Theresistivityofthesoilvarieswidelythroughouttheworldandchangesseasonally.Soilresistivityisdeterminedlargelybyitscontentofelectro-lytes,consistingofmoisture,mineralsanddissolvedsalts.Adrysoilhashighresistivityifitcontainsnosolublesalts.

SoilAshes, cinders, brine, waste

Clay, shale, gumbo, loamSame, with varying proportionsof sand and gravelGravel, sand, stones withlittle clay or loam

590

340

1,020

59,000

2,370

4,060

15,800

94,000

7,000

16,300

135,000

458,000

Resistivity, Ω-cm

Minimum Average Maximum

Table 1

4.1.3 Factors Affecting Soil Resistivity

Twosamplesofsoil,whenthoroughlydried,maybecomeinfactverygoodinsulators, having a resistivity in excess of 109 ohm-centimeters. Theresistivityofthesoilsampleisseentochangequiterapidlyuntilapproxi-matelytwentypercentorgreatermoisturecontentisreached.

02.55

10152030

> 109250,000165,00053,00019,00012,0006,400

> 109150,00043,00018,50010,5006,3004,200

Resistivity, Ω-cmMoisture content,% by weight Top Soil Sandy Loam

Table 2


Theresistivityofthesoilisalsoinfluencedbytemperature.Table3showsthevariationoftheresistivityofsandyloam,containing15.2%moisture,withtemperaturechangesfrom20°to-15°C.Inthistemperaturerangetheresistivityisseentovaryfrom7,200to330,000ohm-centimeters.

201000-5-15

6850

32 (water)32 (ice)

2314

7,2009,90013,80030,00079,000330,000

ResistivityΩ-cm

Temperature

°C °F

Table 3

Becausesoil resistivitydirectly relates tomoisturecontentand temper-ature, it is reasonable to assume that the resistance of any groundingsystemwillvarythroughoutthedifferentseasonsoftheyear.Suchvaria-tionsareshowninFigure6below.Since both temperature and moisture content become more stable atgreaterdistancesbelowthesurfaceoftheearth,itfollowsthatagroundingsystem(tobemosteffectiveatalltimes)shouldbeconstructedwiththegroundroddrivendownaconsiderabledistancebelowthesurfaceoftheearth.Bestresultsareobtainedifthegroundrodreachesthewatertable.

0

20

40

60

80

Jan.

Mar

.

May

July

Sep

t.

Nov

.

Jan.

Mar

.

May

July

Curve 1

Curve 2

Figure 6

Seasonal variation of earth resistance with an electrode of 3/4" pipe in rather stony clay soil. Depth of electrode in earth is 3 ft for Curve 1, and 10 ft for Curve 2.

Insomelocations,theresistivityoftheearthissohighthatlow-resistancegroundingcanbeobtainedonlyatconsiderableexpenseandwithanelab-orategroundingsystem.


Insuchsituations, itmaybeeconomical touseagroundrodsystemoflimitedsizeandtoreducethegroundresistivitybyperiodicallyincreasingthesolublechemicalcontentofthesoil.Table4showsthesubstantialreductioninresistivityofsandyloambroughtaboutbyanincreaseinchemicalsaltcontent.

00.11.05

1020

10,7001,800460190130100

The Effect of Salt* Content on the Resistivity of Soil(sandy loam, moisture content, 15% by weight, temperature 17°C)

Added Salt% by weight of moisture

Resistivity(Ohm-centimeters)

Table 4

Chemicallytreatedsoilisalsosubjecttoconsiderablevariationofresistiv-itywithchangesintemperature,asshowninTable5.Ifsalttreatmentisemployed,itis,ofcourse,necessarytousegroundrodswhichwillresistchemicalcorrosion.

20100-5

-13

110142190312

1440

The Effect of Temperature on the Resistivity of Soil Contining Salt*(sandy loam, 20% moisture; salt 5% of weight of moisture)

Temperature °C Resistivity (Ohm-centimeters)

Table 5

*Suchascoppersulfate,sodiumcarbonateandothers.SaltsmustbeEPAorlocalordinanceapprovedpriortouse.


4.1.4 Effect of Ground Rod Depth on ResistanceToassisttheengineerindeterminingtheapproximategroundroddepthrequired to obtain a desired resistance, a device called theGroundingNomographmaybeused.TheNomograph,shownonthefollowingpage,indicatesthattoobtainagroundingresistanceof20ohmsinasoilwitharesistivityof10,000ohm-centimeters,a5/8"ODrodmustbedriven20ft.Note that the values indicated on theNomograph are based on theassumption that the soil is homogeneous and, therefore, has uniformresistivity(Figure7).TheNomographvalueisanapproximation.

Grounding Nomograph

Ground RodResistance-Ohms

Soil Resistivity(Ohm-centimeters)

Rod DepthFeet

Rod DiameterInches

R

P

D

DIA

20

30

40

90

50

60

70

80

100

15

10

1

5

2

4

3

5/8

1/4

1/2

3/4

1

1.5

8

7

6

5

4

3

2

10000

15000

100000

50000

40000

30000

20000

3000

500

1000

2000

4000

5000

20

30

10090

80

7060

50

40

15

1

2

3

4

5

6

7

8

9

10

K

Figure 7

1. SelectrequiredresistanceonRscale.

2. SelectapparentresistivityonPscale.

3. Lay straightedge on R and P scale, and allow to intersect with Kscale.

4. MarkKscalepoint.

5. LaystraightedgeonKscalepointandDIAscale,andallowtointersectwithDscale.

6. PointonDscalewillberoddepthrequiredforresistanceonRscale.


4.2 Ground Resistance ValuesNEC®2008article250.56regardingtheresistanceofrod,pipeandplateelectrodesstatesthatiftherod,pipe,orplatedoesnothavearesistanceof25Ωorlesstogroundshallbeaugmentedbyoneadditionalelectrodeofanyofthetypesspecifiedby250.52(A)(4)through(A)(8).Wheremultiplerod,pipeorplateelectrodesareinstalledtomeettherequirementsofthesection,theyshallnotbelessthan6feetapart.

FPN:Theparallelingefficiencyofrodslongerthan8feetisimprovedbyspacinggreaterthan6feetapart.

TheNationalElectricalCode®(NEC®)statesthattheresistancetogroundshallnotexceed25Ω.This isanupper limitandguideline,sincemuchlowerresistanceisrequiredinmanyinstances.

“How low in resistance should a ground be?”Anarbitraryanswertothisinohmsisdifficult.Thelowerthegroundresis-tance,thesafer,andforpositiveprotectionofpersonnelandequipment,itisworththeefforttoaimforlessthanoneohm.Itisgenerallyimpracticaltoreachsuchalowresistancealongadistributionsystemoratransmis-sionlineorinsmallsubstations.Insomeregions,resistancesof5Ω or less maybeobtainedwithoutmuchtrouble.Inothers,itmaybedifficulttobringresistanceofdrivengroundsbelow100Ω.

Acceptedindustrystandardsstipulatethattransmissionsubstationsshouldbedesignednottoexceedoneohmresistance.Indistributionsubstations,themaximumrecommendedresistanceis5Ω.Inmostcases,theburiedgridsystemofanysubstationwillprovidethedesiredresistance.

Inlightindustrialorintelecommunicationscentraloffices,5Ωisoftentheacceptedvalue.Forlightningprotection,thearrestersshouldbecoupledwithamaximumgroundresistanceof1Ω.

Theseparameterscanusuallybemetwiththeproperapplicationofbasicgroundingtheory.Therewillalwaysexistcircumstanceswhichwillmakeit difficult to obtain the ground resistance required by theNEC®.Whenthesesituationsdevelop,severalmethodsof loweringthegroundresis-tancecanbeemployed.Theseincludeparallelrodsystems,deepdrivenrod systemsutilizing sectional rods and chemical treatment of the soil.Additionalmethods,discussedinotherpublisheddata,areburiedplates,buried conductors (counterpoise), electrically connected building steel,andelectricallyconnectedconcretereinforcedsteel.


Electricallyconnectingtoexistingwaterandgasdistributionsystemswasoftenconsideredtoyieldlowgroundresistance;however,recentdesignchangesutilizingnon-metallicpipesandinsulatingjointshavemadethismethodofobtaininga lowresistancegroundquestionableand inmanyinstancesunreliable.

Groundrods,ofcourse,willberequiredinhighvoltagetransmissionlines,wheremaximumresistanceof15ohmsisrecommended;andindistribu-tionlines,wheremaximumresistanceof25ohmsispreferred.Allelectri-calsystemsconstructedinaccordancewiththeNationalElectricalCode®, shouldnotexceed25ohms.

The measurement of ground resistances may only be accomplishedwith specially designed test equipment. Most instruments use the Fallof Potential principle of alternating current (AC) circulating between anauxiliaryelectrodeandthegroundelectrodeunder test; thereadingwillbegiveninohmsandrepresentstheresistanceofthegroundelectrodetothesurroundingearth.AEMC®Instrumentshasalsorecentlyintroducedaclamp-ongroundresistancetester.Note: The National Electrical Code® and NEC® are registered trademarks of the National Fire Protection Association.


4.3 Ground Resistance Testing Principle (Fall-of-Potential — 3-Point Measurement)

Three-point measurement is used to measure resistance to ground ofgroundrodsandgrids.ThepotentialdifferencebetweenrodsXandYismeasuredbyavoltmeter,andthecurrentflowbetweenrodsXandZismeasuredbyanammeter.

ByOhm’sLawE=RIorR=E/I,wemayobtain thegroundelectroderesistance R.IfE=20VandI=1A,then:

R===20ohmsEI

201

Itisnotnecessarytocarryoutallthemeasurementswhenusingagroundtester.Thegroundtesterwillmeasuredirectlybygeneratingitsowncur-rentanddisplayingtheresistanceofthegroundelectrode.

ZYX

VOLTMETER (E)

AUXILIARY

POTENTIAL

ELECTRODE

GROUND

ELECTRODE

UNDER TEST

AUXILIARY

CURRENT

ELECTRODE

AMMETER (I)

CURRENT

SUPPLY

R

EARTH

Figure 8


4.3.1 Position of the Auxiliary Electrodes in MeasurementsThegoalinpreciselymeasuringtheresistancetogroundistoplacetheauxiliarycurrentelectrodeZfarenoughfromthegroundelectrodeundertestsothattheauxiliarypotentialelectrodeYwillbeoutsideoftheeffec-tiveresistanceareasofboththegroundelectrodeandtheauxiliarycurrentelectrode.ThebestwaytofindoutiftheauxiliarypotentialrodYisoutsidetheeffectiveresistanceareasistomoveitbetweenXandZandtotakeareadingateachlocation.IftheauxiliarypotentialrodYisinaneffectiveresistancearea(orinbothiftheyoverlap),bydisplacingit,thereadingstakenwillvarynoticeablyinvalue.Undertheseconditions,noexactvaluefortheresistancetogroundmaybedetermined.

X-Y Distance

Re

sis

tan

ce

Reading Variation

Effective Resistance

Areas (Overlapping)

X Y' Y Y'' Z

Figure 9

On the other hand, if the auxiliary potential rodY is located outside oftheeffectiveresistanceareas,asYismovedbackandforththereadingvariationisminimal.Thereadingstakenshouldberelativelyclosetoeachother,andarethebestvaluesfortheresistancetogroundofthegroundX.Thereadingsshouldbeplottedtoensurethattheylieina“plateau”regionasshowninFigure10.

X-Y Distance

Resis

tance

Reading Variation

Effective Resistance

Areas (No Overlap)

X Y Y Y'' Z

Figure 10


4.4 Measuring Resistance of Ground Electrodes

(62% Method)The 62%method has been adopted after graphical consideration andafteractualtest.Itisthemostaccuratemethodbutislimitedbythefactthatthegroundtestedisasingleunit.Thismethodappliesonlywhenallthreeelectrodesareinastraightlineandthegroundisasingleelectrode,pipe,orplate,etc.,asinFigure11.

Alligator Clips

Y ZX52% 62% 72%0% 100% of distance

between X and Z

Ground Rod Y Electrode Z Electrode

Ground Rod

Y Electrode Z Electrode

GroundStrip

-10% 3rdMeasurement

+10% 2ndMeasurement

ΩPress ToMeasure

X-Z

X-Y

X-Y

ZYXC1 P2 C2

Fault

Hi Resistance

Hi Noise



!

®

I N S T R U M E N T S

46.9

Figure 11

ConsiderFigure12,whichshowstheeffectiveresistanceareas(concentricshells)ofthegroundelectrodeXandoftheauxiliarycurrentelectrodeZ.Theresistanceareasoverlap.IfreadingsweretakenbymovingtheauxiliarypotentialelectrodeYtowardseitherXorZ,thereadingdifferentialswouldbegreat andone couldnot obtaina readingwithin a reasonablebandoftolerance.Thesensitiveareasoverlapandactconstantlyto increaseresistanceasYismovedawayfromX.

Distance from Y to Ground Electrode

Resis

tance

Overlapping Effective

Resistance Areas

X Y Z

Ground

Electrode

Under Test

Auxiliary

Potential

Electrode

Auxiliary

Current

Electrode

Figure 12


NowconsiderFigure 13,where theXandZ electrodes are sufficientlyspacedsothattheareasofeffectiveresistancedonotoverlap.Ifweplottheresistance,measuredwefindthatthemeasurementsleveloffwhenYisplacedat62%ofthedistancefromXtoZ,andthatthereadingsoneithersideoftheinitialYsettingaremostlikelytobewithintheestablishedtoleranceband.Thistolerancebandisdefinedbytheuserandexpressedasapercentoftheinitialreading:±2%,±5%,±10%,etc.

Resis

tance

Distance from Y to Ground Electrode

Effective

Resistance

Areas Do

Not Overlap

X Y Z

Ground

Electrode

Under Test

Auxiliary

Potential

Electrode

Auxiliary

Current

Electrode

D

62% of D 38% of D

Resistance ofAuxiliary CurrentElectrode

Resistance of Earth Electrode

Figure 13

4.4.1 Auxiliary Electrode SpacingNodefinitedistancebetweenXandZcanbegiven,sincethisdistanceisrelativetothediameteroftheelectrodetested,itslength,thehomogeneityof the soil tested, andparticularly, the effective resistanceareas.How-ever,anapproximatedistancemaybedeterminedfromthefollowingchartwhichisgivenforahomogeneoussoilandanelectrodeof1"indiameter.(Foradiameterof1/2",reducethedistanceby10%;foradiameterof2"increasethedistanceby10%.)

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 ElectrodesUsing the 62% Method

Table 6


4.5 Ground Resistance Measurement Procedure

(3-Point)

ΩPress To

Measure

X-Z

Xv-Y

Xv-Y

ZYXC1 P2 C2

Fault

Hi Resistance

Hi Noise


AUTORANGINGREFER TO USER MANUAL

FOR FAULT WARNING LIGHT

EXPLANATIONS

!

®


Alligator Clips

Ground Rod

Y Electrode Z Electrode

Ground

Strip

Figure 14

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.

• DisconnectshortinglinkbetweenYandZ(C2,P2)• ConnectXtothegroundrodtobetested• ConnectY(P2)tothecentralelectrode• ConnectZ(C2)totheouterelectrode• Depressthe“Measure”buttontomeasuregroundresistance


4.6 Multiple Electrode SystemAsingledrivengroundelectrodeisaneconomicalandsimplemeansofmakingagoodgroundsystem,butsometimesasinglerodwillnotprovidesufficientlowresistance,andseveralgroundelectrodeswillbedrivenandconnectedinparallelbyacable.Veryoftenwhentwo,threeorfourgroundelectrodesareused,theyaredriveninastraightline.Whenfourormoreareused,ahollowsquarecon-figurationisusedandthegroundelectrodesarestillconnectedinparallelandequallyspaced(Figure15).Inmultipleelectrodesystems,the62%methodelectrodespacingmaynolongerbeapplieddirectly.Thedistanceoftheauxiliaryelectrodesisnowbasedonthemaximumgriddistance(e.g.,inasquare,thediagonal;inaline,thetotallength).Asquarehavingasideof20 ftwillhaveadiagonalofapproximately28ft.

DIAGONAL

DIA

GO

NA

L

a

a a

a

Figure 15


6 ft8 ft10 ft12 ft14 ft16 ft18 ft20 ft30 ft40 ft50 ft60 ft80 ft100 ft120 ft140 ft160 ft180 ft200 ft



Multiple Electrode SystemMax Grid Distance Distance to Y Distance to Z

Table 7


4.7 2-Point Measurement (Simplified Measurement)

Thisisanalternativemethodtothree-pointmeasurementwhen an excel-lent ground is already available.Incongestedareaswherefindingroomtodrivethetwoauxiliarygroundelectrodesmaybeaproblem, the two-pointmeasurementmethodmaybeapplied.Thereadingobtainedwillbethatofthetwogroundsinseries.Therefore,thewaterpipeorothergroundmustbeverylowinresistancesothatitwillbenegligibleinthefinalmeasurement.Theleadresistanceswillalsobemeasuredandshouldbededucted from thefinalmeasure-ment.Thismethod is not as accurate as three-pointmethods (62%method),asitisparticularlyaffectedbythedistancebetweenthetestedelectrodeandthedeadgroundorwaterpipe.Thismethodshouldnotbeusedasastandardprocedure,butratherasabackupintightareas.SeeFigure16.

Procedure:

• ShortYandZ(P2,C2)

• ConnectXtogroundrodtobemeasured

• ConnectZtoanelectrode

• Measureasinthethree-pointmethod

ΩPress ToMeasure

X-Z

X-Y

X-Y

ZYXC1 P2 C2

Fault

Hi RSesistance

Hi Noise



!

®


25.4

Grounding conductor

Ground level

Ground rodButt plate

Utility pole

Terminals shortedAuxiliary rod(Y-Z shorted)

Figure 16


4.8 Continuity MeasurementConnecttheshortingstripsbetweenX(C1),Y(P2)andZ(C2).Continuitymeasurement ismadewith two leads,one fromX, theotherfromY–Z(P2,C2);pushthe“Measure”buttontomeasure.

ΩPress ToMeasure

X-Z

X-Y

X-Y

ZYXC1 P2 C2

Fault

Hi Resistance

Hi Noise



!

®


Figure 17


4.9 How to Use 25Ω Calibration CheckerThecalibrationcheckerhasaresistanceof25Ω.Theproceduretousethecalibrationcheckerisasfollows:

• LoosentheYandZterminals.

• InserttheresistorasshowninFigure18.

• TightendowntheterminalsYandZ.

• Pushdownthe“PresstoMeasure”button.

• Compare thereadingon thedisplay to themeasurement rangeprovidedonthelabel.

NOTE: For alignment purposes of the test resistor, it is recommended that the shorting links remain connected between X, Y and Z.

Forexample, ifacheckwasperformedonthe3640,thedisplayshouldshowareadingbetween24.15Ω and 25.85Ω.Ifso(asinFigure18),theinstrumentisingoodworkingcondition.

LO BAT

ΩPress ToMeasure

X-Z

X-Y

X-Y

ZYXC1 P2 C2

Fault

Hi Resistance

Hi Noise



!

®


3640/461024.15 Ω- 25.85 Ω

460024.05 Ω- 25.95 Ω

362018.75 Ω - 31.25 Ω

25Ω CALIBRATION CHECKER®


Figure 18


CHAPTER 5

MAINTENANCE

5.1 WarningPleasemakesure thatyouhavealready readand fullyunderstand theWARNINGsectiononpage3.

• Toavoidelectricalshock,donotattempttoperformanyservicingunlessyouarequalifiedtodoso.

• Toavoidelectricalshockand/ordamagetotheinstrument,donotgetwaterorother foreignagents into thecase.Turn the instru-mentOFFanddisconnecttheunitfromallcircuitsbeforeopeningthecase.

5.2 Cleaning

NOTE: Disconnect the instrument from any source of electricity.

• Useasoftclothlightlydampenedwithsoapywater.• Rinsewithadampclothandthendrywithadrycloth.

• Donotusealcohol,solventsorhydrocarbons.

5.3 Replacing the Battery• Loosenthetwofasteningscrewsonthebatterycompartmentcover,

whichislocatedonthebottomofthecase(SeeFigure19).

• Removethebatterycompartmentcovertogainaccesstotheeight1.5V“AA”batteries.

• Replacewithnewbatteriesandreassembletheinstrument.


5.4 Replacing the Safety Fuse

NOTE: Do not replace the fuse when the instrument is connected.

To replace the fuse:• Loosen the two fastening screws on the battery compartment

cover,whichislocatedonthebottomofthecase.• Removethebatterycompartmentcovertogainaccesstothefuse

holder.• Replacethefusewiththeappropriatereplacement(0.1A,>250V,

0.25x1.25")andreassembletheinstrument.

! ATTENTIONNE PAS OUVRIR LE BOITIER AVANT D'AVOIRDECONNECTE TOUTES LES ENTREES

! WARNINGDISCONNECT INSTRUMENT FROM ALLINPUTS BEFORE OPENING CASE

Spare

Fuse

Holders

Fuse

Holder

Battery

CompartmentFastening

Screw

Fastening

Screw

Figure 19


Repair and Calibration

Toensurethatyourinstrumentmeetsfactoryspecifications,werecommendthatitbescheduledbacktoourfactoryServiceCenteratone-yearintervalsforcalibration,orasrequiredbyotherstandardsorinternalprocedures.

For instrument repair and calibration:Youmust contactourServiceCenter foraCustomerServiceAuthorizationNumber(CSA#).Thiswillensurethatwhenyourinstrumentarrives,itwillbetrackedandprocessedpromptly.PleasewritetheCSA#ontheoutsideoftheshipping container. If the instrument is returned for calibration,weneed toknowifyouwantastandardcalibration,oracalibrationtraceabletoN.I.S.T.(Includescalibrationcertificateplusrecordedcalibrationdata).

Ship To: ChauvinArnoux®,Inc.d.b.a.AEMC®Instruments 15 Faraday Drive Dover, NH 03820 USA Phone:(800)945-2362(Ext.360) (603)749-6434(Ext.360) Fax: (603)742-2346or(603)749-6309 E-mail:[email protected]

(Orcontactyourauthorizeddistributor)Costsforrepair,standardcalibration,andcalibrationtraceabletoN.I.S.T.areavailable.NOTE: You must obtain a CSA# before returning any instrument.

Technical and Sales Assistance

Ifyouareexperiencinganytechnicalproblems,orrequireanyassistancewiththeproperoperationorapplicationofyourinstrument,pleasecall,mail,faxore-mailourtechnicalsupportteam:

ChauvinArnoux®,Inc.d.b.a.AEMC®Instruments 200FoxboroughBoulevard Foxborough,MA02035USA Phone:(800)343-1391 (508)698-2115 Fax: (508)698-2118 E-mail:[email protected] www.aemc.com

NOTE: Do not ship Instruments to our Foxborough, MA address.


Limited Warranty

The Ground Resistance Tester Model 3640 is warranted to the owner foraperiodof twoyears from thedateoforiginalpurchaseagainstdefects inmanufacture.ThislimitedwarrantyisgivenbyAEMC®Instruments,notbythedistributorfromwhomitwaspurchased.Thiswarrantyisvoidiftheunithasbeentamperedwith,abusedorifthedefectisrelatedtoservicenotperformedbyAEMC®Instruments.

Full warranty coverage and product registration is available on our website at www.aemc.com.

Please print the online Warranty Coverage Information for your records.

What AEMC® Instruments will do:Ifamalfunctionoccurswithinthewarrantyperiod,youmayreturntheinstrumenttousforrepair,providedwehaveyourwarrantyregistrationinformationonfileoraproofofpurchase.AEMC®Instrumentswill,atitsoption,repairorreplacethefaultymaterial.

REGISTER ONLINE AT:www.aemc.com

Warranty Repairs

What you must do to return an Instrument for Warranty Repair: First, request aCustomerServiceAuthorizationNumber (CSA#) by phoneorbyfaxfromourServiceDepartment(seeaddressbelow),thenreturntheinstrumentalongwith thesignedCSAForm.Pleasewrite theCSA#on theoutsideoftheshippingcontainer.Returntheinstrument,postageorshipmentpre-paidto:

Ship To: ChauvinArnoux®,Inc.d.b.a.AEMC®Instruments 15FaradayDrive•Dover,NH03820USA Phone:(800)945-2362(Ext.360) (603)749-6434(Ext.360) Fax: (603)742-2346or(603)749-6309 E-mail:[email protected]

Caution:Toprotectyourselfagainstin-transitloss,werecommendyouinsureyourreturnedmaterial.

NOTE: You must obtain a CSA# before returning any instrument.

NOTES:

CHAUVIN ARNOUX GROUP

®

03/17

99-MAN100440v1

Chauvin Arnoux®, Inc. d.b.a. AEMC® Instruments15FaradayDrive•Dover,NH03820USA•Phone:(603)749-6434•Fax:(603)742-2346

www.aemc.com

digital ground resistance tester model 3640 - aemc.com · tape measure, batteries, carrying bag and...

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