DIGITAL GROUND RESISTANCE AND SOIL RESISTIVITY TESTERS …
Transcript of DIGITAL GROUND RESISTANCE AND SOIL RESISTIVITY TESTERS …
DIGITAL GROUND RESISTANCE AND SOIL RESISTIVITY TESTERS
E N G L I S H User Manual
46204630
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 #: 4620 / 4630
Please fill in the appropriate date as indicated:
Date Received: _________________________________
Date Calibration Due: _______________________
Chauvin Arnoux®, Inc.d.b.a AEMC® Instrumentswww.aemc.com
Digital Ground Resistance Tester Model 4620 and 4630 1
Table of Contents
1. INTRODUCTION ............................................................................... 31.1 International Electrical Symbols ................................................41.2 DefinitionofMeasurementCategories .....................................41.3 ReceivingYourShipment ..........................................................41.4 OrderingInformation .................................................................5
1.4.1 Kits,AccessoriesandReplacementParts ....................6
2. PRODUCT FEATURES ...................................................................... 72.1 ControlandConnectorFeatures (Model4620) ........................72.2 ControlandConnectorFeatures (Model4630) ........................82.3 FaultIndicatorLEDs .................................................................9
2.3.1 X-ZFault .......................................................................92.3.2 Xv-YHighResistance ...................................................92.3.3 Xv-YHighNoise ............................................................9
2.4 Buzzer .....................................................................................102.5 Over-rangeIndication .............................................................102.6 FaultLEDIndication–TipsandSolutions ..............................10
3. SPECIFICATIONS........................................................................... 113.1 Electrical .................................................................................113.2 Mechanical ..............................................................................123.3 Environmental .........................................................................133.4 Safety ......................................................................................133.5 Auto-ranging ...........................................................................13
4. GROUNDING THEORY .................................................................... 144.1 GroundingElectrodeResistance ............................................14
4.1.1 EffectofGroundElectrodeSizeandDepth on Resistance .............................................................164.1.2 EffectsofSoilResistivityonGroundElectrode Resistance ..................................................................174.1.3 FactorsAffectingSoilResistivity .................................184.1.4 EffectofGroundRodDepthonResistance ................21
4.2 GroundResistanceValues .....................................................22
2 Digital Ground Resistance Tester Model 4620 and 4630
4.3 GroundResistanceTestingPrinciple .....................................244.3.1 PositionofAuxiliaryElectrodesinMeasurements ......25
4.4 MeasuringResistanceofGroundElectrodes ........................264.4.1 AuxiliaryElectrodeSpacing ........................................28
4.5 MultipleElectrodeSystem ......................................................28
5. OPERATION .................................................................................. 305.1 GroundResistanceMeasurementProcedure .......................305.2 2-PointMeasurement(SimplifiedMeasurement) ...................315.3 ContinuityMeasurement .........................................................325.4 SoilResistivityMeasurements ................................................32
5.4.1 PurposesofSoilResistivity ........................................325.4.2 TypesofResistivityMeasurements ............................33
5.5 SoilResistivityMeasurementProcedure (4-Point) .................345.6 How to Use 25ΩCalibrationChecker(optionalaccessory) ....36
6. MAINTENANCE ............................................................................. 376.1 Warning..................................................................................376.2 Disassembly ...........................................................................376.3 PowerSupply ..........................................................................38
6.3.1 TestingtheBattery ......................................................386.3.2 ReplacingtheBattery(Model4620) ...........................396.3.3 RechargingtheBattery(Model4630) .........................396.3.4 ReplacingtheSafetyFuse ..........................................40
6.4 Cleaning ..................................................................................406.5 Storage ...................................................................................40
RepairandCalibration ...........................................................................41
TechnicalandSalesAssistance ............................................................41
Limited Warranty ...................................................................................42
WarrantyRepairs ...................................................................................42
Digital Ground Resistance Tester Model 4620 and 4630 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
Thesesafetywarningsareprovidedtoensurethesafetyofper-sonnelandproperoperationoftheinstrument.• The instrumentmust not be operated beyond its specified
operatingrange.• Safetyistheresponsibilityoftheoperator.• Allmetalobjectsorwiresconnectedtotheelectricalsystem
shouldbeassumedtobelethaluntiltested.Groundingsys-temsarenoexception.
• Useextremecautionwhenusingtheinstrumentaroundener-gizedelectricalequipment.
• Neverattempttousetheinstrumenttotwistorprythegroundelectrode or ground wire away from the equipment beinggrounded.
• AEMC®Instrumentsconsiderstheuseofrubberglovestobeanexcellentsafetypracticeeveniftheequipmentisproperlyoperatedandcorrectlygrounded.
• Alwaysinspecttheinstrumentandleadspriortouse.Replaceanydefectivepartsimmediately.
4 Digital Ground Resistance Tester Model 4620 and 4630
1.1 International Electrical Symbols
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/or 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 I: Formeasurementsoncircuitsnotdirectlyconnected to theAC
supplywall outlet such as protected secondaries, signal level,andlimitedenergycircuits.
CAT II: Formeasurements performed on circuits directly connected totheelectricaldistributionsystem.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,makesure that thecontentsareconsis-tentwith thepacking list.Notifyyourdistributorofanymissing items. Iftheequipmentappearstobedamaged,fileaclaimimmediatelywiththecarrierandnotifyyourdistributoratonce,givingadetaileddescriptionofanydamage.Savethedamagedpackingcontainertosubstantiateyourclaim.Donotuseequipmentwhichisdamagedorappearstobedamaged.
Digital Ground Resistance Tester Model 4620 and 4630 5
1.4 Ordering Information
Ground Resistance Tester Model 4620 ............................Cat. #2130.43Includes ground tester workbook CD, 8 C cell batteries, user manual, and product warranty and registration card.
Ground Resistance Tester Model 4620 Kit (150 ft) .........Cat. #2135.19Includes 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, ground tester workbook CD, batteries, carrying bag, user manual and warranty card.
Ground Resistance Tester Model 4620 Kit (300 ft) .........Cat. #2135.20Includes 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, ground tester workbook CD, batteries, carrying bag, user manual and warranty card.
Ground Resistance Tester Model 4620 Kit (500 ft) .........Cat. #2135.21Includes 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, ground tester workbook CD, batteries, carrying bag, user manual and warranty card.
Ground Resistance Tester Model 4630 ............................Cat. #2130.44Includes ground tester workbook CD, rechargeable battery, AC power cord, user manual and product warranty and registration card.
Ground Resistance Tester Model 4630 Kit (150 ft) .........Cat. #2135.22Includes 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, ground tester workbook CD, batteries, carrying bag, user manual and warranty card.
Ground Resistance Tester Model 4630 Kit (300 ft) .........Cat. #2135.23Includes 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, ground tester workbook CD, batteries, carrying bag, user manual and warranty card.
Ground Resistance Tester Model 4630 Kit (500 ft) .........Cat. #2135.24Includes 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, ground tester workbook CD, batteries, carrying bag, user manual and warranty card.
6 Digital Ground Resistance Tester Model 4620 and 4630
1.4.1 Kits, Accessories and Replacement Parts
Test Kit for 3-Point Testing (150 ft) ..................................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 and carrying bag.
Test Kit for 4-Point Testing (300 ft) ..................................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 and carrying bag.
Test Kit for 4-Point Testing (500 ft) ..................................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 and 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 and carrying bag.
25Ω 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
Order Accessories and Replacement Parts Directly OnlineCheck our Storefront at www.aemc.com/store for availability
Digital Ground Resistance Tester Model 4620 and 4630 7
CHAPTER 2
PRODUCT FEATURES
2.1 Control and Connector Features (Model 4620)
Ω
1. Low battery indicator2. Input terminal Z (H)3. Input terminal Y (S)4. Input terminal Xv (ES)5. Input terminal X (E)6. X-Z Fault indicator
Figure 1
7. Xv-Y High Resistance indicator 8. Xv-Y High Noise indicator 9. Display (with backlight)10. Fuse holder11. Test button
2
1
3
4
5
11
10
9
86 7
8 Digital Ground Resistance Tester Model 4620 and 4630
2.2 Control and Connector Features (Model 4630)
Ω
1. Low battery indicator2. AC power input3. Input terminal Z (H)4. Input terminal Y (S)5. Input terminal Xv (ES)6. Input terminal X (E)
Figure 2
7. X-Z Fault indicator 8. Xv-Y High Resistance indicator 9. Xv-Y High Noise indicator10. Display (with backlight)11. Fuse holder12. Test button
3
2
1
4
5
6
12
11
10
97 8
Digital Ground Resistance Tester Model 4620 and 4630 9
2.3 Fault Indicator LEDsThethreeindicatorsconfirmthatthecorrectmeasurementisbeingtaken,ifnoneofthemarelit.
2.3.1 X-Z Fault
ThisLEDsignalsthatthevoltagebetweenterminalsXandZexceeds30Vpeak.Therearefourpossiblecauses:
• theresistanceofthecurrentcircuitbetweenXandZistoohigh• interferencevoltageinthecurrentcircuitistoohigh• thefuseisblown• thecircuitisopen(leadnotconnected)
2.3.2 Xv-Y High ResistanceThisLEDsignalsthattheresistanceinthevoltagecircuit(betweenXvandYorXandY)istoohigh(approx50kΩ)orthatthecircuitmaybeopen.
• Flashingwill continue throughout themeasurement,even if theresistance drops below the threshold (e.g. after reconnectingor lowering auxiliary rod resistance). In this case, you mustreleasethepush-buttonandpressagainafterthefaulthasbeencorrected.
• Occasionally, a stray voltage above 4.5Vmay also set off thislight.
• Checktheleadsforapossiblesolution.
2.3.3 Xv-Y High NoiseThisLEDsignals thepresenceof excessiveelectrical noise (13Vpeakapprox)inthevoltagecircuit(betweenXvandYorXandY).
• Oneremedyistouseshieldedleadsfromtheinstrumenttotheauxiliaryelectrodes.
• Connectalltheshieldstotherodundertest.
10 Digital Ground Resistance Tester Model 4620 and 4630
2.4 BuzzerTheModels4620and4630featureabuzzer,whichwillsoundwhentheterminals of the tester are connected to a voltage source. The soundvolume is proportional to the voltage up to 30V approximately, thenbecomes stable.
2.5 Over-range IndicationOver-rangeisindicatedwhenthedisplayreads1,orwhenthedisplayisblinkingandtheindicatorislit.
2.6 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:XandZorXvandYrodsarereversed.
NOTE: Accuracy may be affected by auxiliary ground rod (Ry, Rz) resistance levels and by stray signal levels (earth currents).
Digital Ground Resistance Tester Model 4620 and 4630 11
CHAPTER 3
SPECIFICATIONS
3.1 ElectricalMeasurement Range: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 2% 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: 4to8secondsapproxforastabilizedmeasurement
Interference:TheModels4620&4630aredesignedtorejecthighlevelsofinterferencevoltage(DC,50/60Hz,harmonics)
• DCvoltageinserieswithX:20V• ACvoltageinserieswithY:13Vpeak(@16.67,50,60,400Hz)• ACvoltageinserieswithZ:32Vpeak(@16.67,50,60,400Hz)
Accuracies and specifications are given for an ambient temperature of 23°C ±3°K, RH of 45 to 55%, battery power at 9.5V, auxiliary resistance at the measurement terminals = 0, no stray voltage, an electrical field < 1V/m, and a magnetic field from 0 to 40A/m.
Voltage Detection Range:20to250VACbetweentheXandZterminalsorbetweentheXvandZterminals.
Frequency: DCat450Hz
Voltage Withstanding:Bothmodelsarefuseprotected.Intheeventofasystemfault,theunitscanwithstand250VACor100VDC.
Fuse Protection: Highbreakingcapacity-0.1A,>250V,0.25x1.25"
12 Digital Ground Resistance Tester Model 4620 and 4630
Model 4620
Power Source: Eight1.5VCcellbatteries
Battery Life: 4500measurementsof15secondseach
Low Battery Indicator: Ifthe indicatorlightsup,thebatteriesarelosingpower.
Model 4630
Power Source:NiMHrechargeablecell(4630)
Battery Life: 2000measurementsof15secondseach
Battery Charging:Externalrecharge-120-230V/50-60Hz,20VAChargetime-6hrstoattain80%ofthebatterycapacity
Low Battery Indicator: Ifthe“CHARGE”indicatorturnsonsolidRED,thebatteryneedstobecharged.
3.2 MechanicalConnection:Color-codedterminalsacceptspadelugswithminimumgapof6mmorstandard4mmbananajacks.
Display:2000-count7segmentLCD,approx1"high(3-1/2digit)LCDalsoindicatesoverrange,testleadshortsandleadreversals.Blueelectroluminescentbacklight.
Dimensions:10.8x9.7x5.0"(273x247x127mm)
Weight:Model4620:6.28lbs(2.85kg)Model4630:7.38lbs(3.35kg)
Colors:Case-safetyyellow;Frontpanel-gray
Mechanical Protection:TheModels4620and4630havesuccessfullyundergonealltherequiredmechanicaltestsandthereforemeetalltherequirementsofthestandardsEN61557andEN61010-1.
Digital Ground Resistance Tester Model 4620 and 4630 13
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
Electrical:EN61010-1+A2(ed.95)EN61557(ed.97)30Vrms,CATIII,PollutionDegree2
Electromagnetic Compatibility:EN61326-1(ed.98)
*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.
14 Digital Ground Resistance Tester Model 4620 and 4630
CHAPTER 4
GROUNDING THEORY
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
Digital Ground Resistance Tester Model 4620 and 4630 15
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.
In theory, the ground resistancemay be derived from the general for-mula:
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 = ρ2πL
In -1
R=resistanceinohmsofthegroundrodtotheearth(orsoil)
L=groundingelectrodelength
r=groundingelectroderadius
ρ=averageresistivityinohms-cm
16 Digital Ground Resistance Tester Model 4620 and 4630
4.1.1 Effect of Ground Electrode Size and Depth on Resistance
Size: Increasing thediameter of the roddoesnotmaterially reduce itsresistance.Doublingthediameterreducesresistancebylessthan10%.
0
25
50
75
100
1/2 5/8 3/4 1 1 1/4 1 1/2 1 3/4
Rod Diameter (inches)
Resis
tance 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
Re
sis
tan
ce
in
Oh
ms
1/2" dia.1" dia.
Figure 5
Digital Ground Resistance Tester Model 4620 and 4630 17
TheNEC®2008250.52(A)(5)requiresaminimumof8ft(2.4m)tobeincontactwiththesoil.Themostcommonisa10ft(3m)cylindricalrodwhichmeetstheNEC®code.Aminimumdiameterof5/8"(1.59cm)isrequiredforsteelrodsand1/2"(1.27cm)forcopperorcoppercladsteelrodsNEC® 2008250.52(A)(5)(a)(b).Minimumpracticaldiameterfordrivinglimitationsfor10ft(3m)rodsare:
• 1/2"(1.27cm)inaveragesoil• 5/8"(1.59cm)inmoistsoil• 3/4"(1.91cm)inhardsoilormorethan10ftdrivingdepths
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.
Soil
Ashes, cinders, brine, waste
Clay, shale, gumbo, loam
Same, with varying proportions
of sand and gravel
Gravel, sand, stones with
little clay or loam
590
340
1020
59,000
2370
4060
15,800
94,000
7000
16,300
135,000
458,000
Resistivity, Ω-cm
Minimum Average Maximum
Table 1
18 Digital Ground Resistance Tester Model 4620 and 4630
4.1.3 Factors Affecting Soil Resistivity
Twosamplesofsoil,whenthoroughlydried,maybecomeinfactverygoodinsulators,havingaresistivityinexcessof109ohm-centimeters.Theresis-tivityofthesoilsampleisseentochangequiterapidlyuntilapproximatelytwentypercentorgreatermoisturecontentisreached.
0
2.5
5
10
15
20
30
> 109
250,000
165,000
53,000
19,000
12,000
6400
> 109
150,000
43,000
18,500
10,500
6300
4200
Resistivity, Ω-cmMoisture content,
% by weight Top Soil Sandy Loam
Table 2
Theresistivityofthesoilisalsoinfluencedbytemperature.Table3showsthevariationoftheresistivityofsandyloam,containing15.2%moisture,withtemperaturechangesfrom20°to-15°C.Inthistemperaturerangetheresistivityisseentovaryfrom7200to330,000ohm-centimeters.
20
10
0
0
-5
-15
68
50
32 (water)
32 (ice)
23
14
7200
9900
13,800
30,000
79,000
330,000
Resistivity
Ω-cm
Temperature
°C °F
Table 3
Digital Ground Resistance Tester Model 4620 and 4630 19
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
Sept.
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.
20 Digital Ground Resistance Tester Model 4620 and 4630
Insomelocations,theresistivityoftheearthissohighthatlow-resistancegroundingcanbeobtainedonlyatconsiderableexpenseandwithanelab-orategroundingsystem.Insuchsituations, itmaybeeconomical touseagroundrodsystemoflimitedsizeandtoreducethegroundresistivitybyperiodicallyincreasingthesolublechemicalcontentofthesoil.Table4showsthesubstantialreductioninresistivityofsandyloambroughtaboutbyanincreaseinchemicalsaltcontent.
0
0.1
1.0
5
10
20
10,700
1800
460
190
130
100
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
Chemicallytreatedsoilisalsosubjecttoconsiderablevariationofresistivitywithchangesintemperature,asshowninTable5.If salt treatment is employed, it is necessary to use auxiliary groundelectrodes,whichwillresistchemicalcorrosion.
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
*Such as copper sulfate, sodium carbonate and others. Salts must be EPA or local ordinance approved prior to use.
Digital Ground Resistance Tester Model 4620 and 4630 21
4.1.4 Effect of Ground Rod Depth on ResistanceToassisttheengineerindeterminingtheapproximategroundroddepthrequired to obtain a desired resistance, a device called theGroundingNomographmaybeused.TheNomograph,showninFigure7,indicatesthattoobtainagroundingresistanceof20ohmsinasoilwitharesistivityof10,000ohm-centimeters,a5/8"ODrodmustbedriven20ft.NotethatthevaluesindicatedontheNomographarebasedontheassumptionthatthesoilishomogeneousand,therefore,hasuniformresistivity.TheNomo-graphvalueisanapproximation.
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 K
scale.4. MarkKscalepoint.5. LaystraightedgeonKscalepointandDIAscale,andallowtointersect
withDscale.6. PointonDscalewillberoddepthrequiredforresistanceonRscale.
22 Digital Ground Resistance Tester Model 4620 and 4630
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,recentdesign
Digital Ground Resistance Tester Model 4620 and 4630 23
changesutilizingnon-metallicpipesandinsulatingjointshavemadethismethodofobtaininga lowresistancegroundquestionableand inmanyinstancesunreliable.
Auxiliarygroundelectrodeswillberequiredinhighvoltagetransmissionlines,wheremaximum resistance of 15 ohms is recommended, and indistributionlines,wheremaximumresistanceof25ohmsispreferred.AllelectricalsystemsconstructedinaccordancewiththeNationalElectricalCode®,shouldnotexceed25ohms.
Themeasurementofgroundresistancesmayonlybeaccomplishedwithspeciallydesignedtestequipment.MostinstrumentsusetheFallofPoten-tial principleofalternatingcurrent (AC)circulatingbetweenanauxiliaryelectrodeandthegroundelectrodeundertest;thereadingwillbegiveninohmsandrepresentstheresistanceofthegroundelectrodetothesur-roundingearth.AEMC®Instrumentshasalsorecentlyintroducedaclamp-ongroundresistancetester.
The National Electrical Code® and NEC® are registered trademarks of the National Fire Pro-tection Association.
24 Digital Ground Resistance Tester Model 4620 and 4630
4.3 Ground Resistance Testing Principle (Fall-of-Potential — 3-Point Measurement)
3-Pointmeasurementisusedtomeasureresistancetogroundofauxiliarygroundelectrodesandgrids.ThepotentialdifferencebetweenrodsXandYismeasuredbyavoltmeter,andthecurrentflowbetweenrodsXandZismeasuredbyanammeter.
ByOhm’sLawE=RIorR=E/I,wemayobtain thegroundelectroderesistance R.IfE=20VandI=1A,then:
R===20ohmsEI
201
Itisnotnecessarytocarryoutallthemeasurementswhenusingagroundtester.Thegroundtesterwillmeasuredirectlybygeneratingitsowncur-rentanddisplayingtheresistanceofthegroundelectrode.
Z (H)Y (S)X (E)
VOLTMETER (E)
AUXILIARY
POTENTIAL
ELECTRODE
GROUND
ELECTRODE
UNDER TEST
AUXILIARY
CURRENT
ELECTRODE
AMMETER (I)
CURRENT
SUPPLY
R
EARTH
Figure 8
NOTE: Terminals X and Xv are shorted together in 3-Point measurement.
Digital Ground Resistance Tester Model 4620 and 4630 25
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
26 Digital Ground Resistance Tester Model 4620 and 4630
4.4 Measuring Resistance of Ground Electrodes (62% Method)
The62%methodhasbeenadoptedaftergraphicalconsiderationandafteractualtest.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
Ω
Figure 11
ConsiderFigure12,whichshowstheeffectiveresistanceareas(concentricshells)ofthegroundelectrodeXandoftheauxiliarycurrentelectrodeZ.Theresistanceareasoverlap.
If readings were taken by moving the auxiliary potential electrode YtowardseitherXorZ, the readingdifferentialswouldbegreatandonecould not obtain a readingwithin a reasonable band of tolerance.ThesensitiveareasoverlapandactconstantlytoincreaseresistanceasYismovedawayfromX.
Digital Ground Resistance Tester Model 4620 and 4630 27
Distance from Y to Ground Electrode
Re
sis
tan
ce
Overlapping Effective
Resistance Areas
X Y Z
Ground
Electrode
Under Test
Auxiliary
Potential
Electrode
Auxiliary
Current
Electrode
Figure 12
NowconsiderFigure 13,where theXandZelectrodesare 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
28 Digital Ground Resistance Tester Model 4620 and 4630
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 Electrodes
Using the 62% Method
Table 6
4.5 Multiple Electrode SystemAsingledrivengroundelectrodeisaneconomicalandsimplemeansofmakingagoodgroundsystem,butsometimesasinglerodwillnotprovidesufficientlowresistance,andseveralgroundelectrodeswillbedrivenandconnectedinparallelbyacable.
Veryoftenwhentwo,threeorfourgroundelectrodesareused,theyaredriveninastraightline.Whenfourormoreareused,ahollowsquarecon-figurationisusedandthegroundelectrodesarestillconnectedinparallelandequallyspaced(Figure14).
Inmultipleelectrodesystems,the62%methodelectrodespacingmaynolongerbeapplieddirectly.Thedistanceoftheauxiliaryelectrodesisnowbasedonthemaximumgriddistance(e.g.inasquare,thediagonal;inaline,thetotallength).Asquarehavingasideof20 ftwillhaveadiagonalofapproximately28ft.
Digital Ground Resistance Tester Model 4620 and 4630 29
DIAGONAL
DIA
GO
NA
L
a
a a
a
Figure 14
6 ft
8 ft
10 ft
12 ft
14 ft
16 ft
18 ft
20 ft
30 ft
40 ft
50 ft
60 ft
80 ft
100 ft
120 ft
140 ft
160 ft
180 ft
200 ft
78 ft
87 ft
100 ft
105 ft
118 ft
124 ft
130 ft
136 ft
161 ft
186 ft
211 ft
230 ft
273 ft
310 ft
341 ft
372 ft
390 ft
434 ft
453 ft
125 ft
140 ft
160 ft
170 ft
190 ft
200 ft
210 ft
220 ft
260 ft
300 ft
340 ft
370 ft
440 ft
500 ft
550 ft
600 ft
630 ft
700 ft
730 ft
Multiple Electrode System
Max Grid Distance Distance to Y Distance to Z
Table 7
30 Digital Ground Resistance Tester Model 4620 and 4630
CHAPTER 5
OPERATION
5.1 Ground Resistance Measurement Procedure (3-Point)
Alligator ClipsGround Rod
XY Electrode Z Electrode
GroundStrip
Ω
Figure 15
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.
• XandXv(E,ES)areshorted• DisconnectshortinglinkbetweenYandZ(S,H)• ConnectXtothegroundrodtobetested• ConnectY(S)tothecenterelectrode• ConnectZ(H)totheouterelectrode• Depressthe“Test”buttontomeasuregroundresistance
Digital Ground Resistance Tester Model 4620 and 4630 31
5.2 2-Point Measurement (Simplified Measurement)
Thisisanalternativemethodto3-Pointmeasurementwhen an excellent ground is already available.
Incongestedareaswherefindingroomtodrivethetwoauxiliarygroundelectrodesmaybeaproblem,the2-Pointmeasurementmethodmaybeapplied.The readingobtainedwillbe thatof the twogrounds inseries.Therefore,thewaterpipeorothergroundmustbeverylowinresistancesothatitwillbenegligibleinthefinalmeasurement.Theleadresistanceswillalsobemeasuredandshouldbededucted from thefinalmeasure-ment.Thismethodisnotasaccurateas3-Pointmethod(62%method),asitisparticularlyaffectedbythedistancebetweenthetestedelectrodeandthedeadgroundorwaterpipe.Thismethodshouldnotbeusedasastandardprocedure,butratherasabackupintightareas.
Procedure:• ShortXandXv(E,ES)• ShortYandZ(S,H)• ConnectXtogroundrodtobemeasured• ConnectZtoanelectrode• Measureasinthe3-Pointmethod
Grounding conductor
Ground
level
Ground
rodButt plate
Utility
pole
Terminals shorted
Metallic Water Pipe
(Y-Z shorted)
Ω
Figure 16
32 Digital Ground Resistance Tester Model 4620 and 4630
5.3 Continuity MeasurementConnecttheshortinglinksbetweenXandXv(E,ES),andY(S)andZ(H).Continuitymeasurementismadewithtwoleads,onefromX-Xv,theotherfromY-Z(S,H).Pushthe“Test”buttontomeasurecontinuity.Thisisagoodtesttoverifybondingbetweengroundingelectrodeandthegroundwire.
4620 and 4630
Ω
Figure 17
5.4 Soil Resistivity Measurements
5.4.1 Purposes of Soil Resistivity
Soilresistivitymeasurementshavethreepurposes:
1. Suchdata isused tomakesub-surfacegeophysical surveysasanaidinidentifyingorelocations,depthtobedrockandothergeologicalphenomena.
2. Resistivityhasadirect impacton thedegreeofcorrosion inunder-groundpipelines.A decrease in resistivity relates to an increase incorrosiveactivityandthereforedictatestheprotectivetreatmenttobeused.
Digital Ground Resistance Tester Model 4620 and 4630 33
3. Soilresistivitydirectlyaffectsthedesignofagroundingsystem,andit is to that task that thisdiscussion isdirected.Whendesigninganextensivegroundingsystem,itisadvisabletolocatetheareaoflowestsoil resistivity in order to achieve the most economical groundinginstallation.
5.4.2 Types of Resistivity Measurements
Therearetwotypesofresistivitymeasurements:• 2-Pointmethod The2-Pointmethodissimplytheresistancemeasuredbetween
twopoints.
• 4-Pointmethod Formostapplications, themostaccuratemethod is the4-Point
method,which is used by theAEMC® InstrumentsModel 4620and 4630 Ground Testers. The 4-Point method, as the nameimplies,requirestheinsertionoffourequallyspaced,in-lineelec-trodesintothetestarea.Aknowncurrentfromaconstantcurrentgeneratorispassedbetweentheoutermostelectrodes(XandZ).Thepotentialdrop(afunctionoftheresistance)isthenmeasuredacrossthetwoinnermostelectrodes(XvandY).TheModels4620and4630arecalibratedtoreaddirectlyinohms.
b<A
20 A A A
Z electrodeY electrodeXv electrodeX electrode
Ω
Figure 18
34 Digital Ground Resistance Tester Model 4620 and 4630
5.5 Soil Resistivity Measurement Procedure (4-Point)
Givenasizeabletractoflandinwhichtodeterminetheoptimumsoilresis-tivity,someintuitionisinorder.Assumingthattheobjectiveislowresis-tivity, preference should be given to an area containingmoist loam asopposed toadry sandyarea.Considerationmustalsobegiven to thedepthatwhichresistivityisrequired.
• DisconnecttheshortinglinkfromtheXandXvterminals.• Arrangetheelectrodes inastraight line.Besurethatdistances
between electrodes are identical. Example:10ftbetweeneachelectrodeforauxiliarygroundelec-
trodesthatwillbedriven10ftdeep(SeeFigure18).• Thedistancebetweenpolesisproportionaltotheaveragedepth
ofthesoilsampleyouwishtomake.• Theelectrodesshouldbeplacedatadepthofapproximately6"
(0.15m),sothatthedepthisapproximately1/20thofthedistancebetween electrodes.
• UseleadstoconnecttheX,Xv,Y,andZelectrodestotherespec-tiveterminalsontheDigitalGroundResistanceTester.
• Pressthe“Test”button.• Readtheresistancelevel(R)indicatedonthedisplay.• In the event of difficulties in performing measurements,
consult the previous instructions concerning ground resistancemeasurements.
• Applythefollowingformulainordertodetermineresistivity(ρ):
ρ = 2πxRxA
A = distance between electrodes in cm
ρ = resistivity in Ωcm
R=ohmsreadingobtainedonModel4620/4630
Example 1: For measurement performed in soil with a high limestone content, the reading is R = 225Ω, with A = 300cm (3m).
ρ = 2πx225Ωx300cm
ρ=423,900Ωcm
Digital Ground Resistance Tester Model 4620 and 4630 35
Example 2: After inspection, the area to be investigated has been narrowed down to a plot of ground approximately 75 square feet (22.5m2). Assume that you need to determine the resistivity at a depth of 15 ft (457cm). The distance “A” between the electrodes must then be equivalent to the depth at which average resistivity is to be determined (15ft or 450cm). Using the more simplified Wenner formula (ρ = 2πAR), the electrode depth must then be 1/20th of the electrode spacing or 8-7/8" (22.5cm). If the electrode spacing is greater than 1/20th of the electrode spacing, the following formula must be used:
ρ =4πAR
1 + 2A
(A2 + 4B2)
2A
(4A2 + 4B2)
Layout theelectrodes inagridpattern (Figure20)andconnect to theModel4630asshowninFigure19.Proceedasfollows:
• RemovetheshortinglinkbetweenXandXv
• Connectallfourauxiliarygroundelectrodes
Example 3: If the reading is R = 15:
ρ(resistivity)=2πxRxA
A(distancebetweenelectrodes)=450cm
ρ=6.28x15x450=42,390Ωcm
R
B
X Xv Y Z
AA A
Ω
Figure 19
36 Digital Ground Resistance Tester Model 4620 and 4630
AAA
A
A
A
Figure 20
5.6 How to Use 25Ω Calibration Checker (optional accessory)
The calibration checker is good for both the 4620 and 4630. It has aresistance of 25Ω. The procedure to use the calibration checker is asfollows:
• LoosentheX,Xv,YandZterminals.• InsertthecalibrationcheckerasshowninFigure21.• TightendowntheterminalsX,Xv,YandZ.• Pushdownthe“Test”button.• Compare thereadingon thedisplay to themeasurement range
providedbelow.
NOTE: For alignment purposes of the calibration checker, it is recommended that the shorting links remain connected.
If a check performed on the Model 4630 or 4620 displays a readingbetween 24.1Ω and 25.9Ω (as inFigure21), the instrument is in goodworkingcondition.Thereadingsareforanambienttemperaturebetween68°and79°F(25°C±3°C).
25
Ω C
AL
IBR
AT
ION
CH
EC
KE
R
®
INSTRUMENTS
Ω
Figure 21
Digital Ground Resistance Tester Model 4620 and 4630 37
CHAPTER 6
MAINTENANCE
6.1 Warning
Please make sure that you have already read and fully understand the WARN-ING section on page 3.
• Toavoidelectricalshock,donotattempttoperformanyservicingunlessyouarequalifiedtodoso.
• Toavoidelectricalshockand/ordamagetotheinstrument,donotgetwaterorotherforeignagentsintothecase.
• TurntheinstrumentOFFanddisconnecttheunitfromallcircuitsbeforeopeningthecase.
• Usespecifiedsparepartsonly.
6.2 DisassemblyNecessary equipment:
• ATorxACX.10screwdriverorsimilar• APhillipsscrewdriver
WiththePhillipsscrewdriver,removethe4screws(1)atthebackofthecaseandfreetheinternalunit(2)fromtheyellowcase(3).
38 Digital Ground Resistance Tester Model 4620 and 4630
To open the internal unit:• Settheunitupside-downonthetableandopenthebatterycompart-
ment(4)byremovingthe2Phillipsscrewsholdingthelatch.Then,freethebattery(5)orthebatteries(dependingonthetypeofinstrument).
• Removethe2Torxscrews(6) in thebottomof thebatterycompart-ment.
• Togetaccesstothetwoconnectors(9)linkingthepowersupplyand
displayboardstogether,liftupthecoveroftheinternalunit.Oncetheseconnectorsarefree,itispossibletocompletelypullawaythebottompartfromthecover.
• Thedisplayboard(7)isconnectedtothefrontplate.• Thepowersupplyboard(8)isconnectedtothebottomofthebody.
To free the display board from the cover:• Removethe3Phillipsscrewsandunsolderallthewiresconnect-
ingtotheterminalsandtothefuse.
To free the power supply board from the bottom of the body:• Removethe6Phillipsscrewsatthebackofthebodyanddiscon-
necttheconnectorcomingfromthebattery.
6.3 Power Supply
6.3.1 Testing the Battery• Short-circuittheXandZterminals.• Pressthe“TEST”button.• Ifthelowbatteryorchargeindicatorlightsuponthedisplayyou
willneedtoreplaceorrechargethebatteries.
Digital Ground Resistance Tester Model 4620 and 4630 39
6.3.2 Replacing the Battery (Model 4620)• Detachthefourscrewsonthebottomoftheyellowcase.• Removetheshellandfrontpanelassembly.• Unscrew the two fasteningscrewson thebatterycompartment,
thenremovethecover.• Removethe8batteriesandreplacethem.
To replace thebatterieswith rechargeablecells (1.2V -2Ahorabove,NiCdorNiMHofthesamesize):
• Removetheplugunderthebatteries.• Settheswitchtotheposition:NiCd/NiMH• Replacetheplug.• Insertthe8rechargeablecells.
NOTE: The Model 4620 does not have a built-in battery charger. The rechargeable cells will need to be charged outside the instrument.
6.3.3 Recharging the Battery (Model 4630)• Connectthebatterychargeconnectortothemains.• TheCHARGEindicatorlightwillturnred.• Whenthebatteryischarged,theCHARGEindicatorwillbecome
green.• The charge time is approximately 6 hrs for 80% of the battery
capacity.
To achieve maximum charge capacity:• Disconnectthepowercord(thegreenLEDwillgooutinapproxi-
mately20sec).• Reconnectthepowercord.Thechargewillresumewherethefirst
chargeleftoff,andcontinueuntilmaximumcapacityisachieved.
NOTE: If the unit has been stored for a long period of time, recharge the bat-tery before use.
NOTE: 1/2 hr charge provides enough power for one day of measurements (approx 135 measurements lasting 15 sec).
40 Digital Ground Resistance Tester Model 4620 and 4630
6.3.4 Replacing the Safety Fuse
Tocheckthefusecontinuity,shortcircuittheXandZterminalsandmakeameasurement.IftheFAULTindicatorlightflashes,itmeansthatthefuseis blown.
Toreplacethefuse:
NOTE: Do not replace the fuse when the instrument is connected.
• Thefuseislocatedonthefrontofthefaceplate.• Usingascrewdriver,turnthescrewaquarterofaturn.• Takeoutthesupportcontainingthefuse.• Replacethefuse(0.1A,>250V,0.25x1.25").• Replacethesupportandscrewitbackin.
6.4 Cleaning
NOTE: Disconnect the instrument from any source of electricity.
• Useasoftclothlightlydampenedwithsoapywater.• Rinsewithadampclothandthendrywithadrycloth.• Donotusealcohol,solventsorhydrocarbons.
6.5 StorageIf theModel4620 isnotused fora longperiodof time (twomonthsormore),removethebatteriesandstorethemseparately.
If theModel4630 isnotused fora longperiodof time (twomonthsormore),itisrecommendedtochargethebatteryforafewhours.
Digital Ground Resistance Tester Model 4620 and 4630 41
Repair and Calibration
Toensurethatyourinstrumentmeetsfactoryspecifications,werecommendthatitbescheduledbacktoourfactoryServiceCenteratone-yearintervalsforrecalibration,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,NH03820USA 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.
42 Digital Ground Resistance Tester Model 4620 and 4630
Limited Warranty
TheModels4620and4630arewarrantedtotheownerforaperiodofoneyearfromthedateoforiginalpurchaseagainstdefectsinmanufacture.Thislimitedwarranty isgivenbyAEMC® Instruments,notby thedistributor fromwhomitwaspurchased.Thiswarrantyisvoidiftheunithasbeentamperedwith,abusedor if thedefect is related toservicenotperformedbyAEMC® Instruments.
For full and detailed warranty coverage, please read the Warranty Coverage Information, which is attached to the Warranty Registration Card (if enclosed) or is available at www.aemc.com. Please keep the Warranty Coverage Information with your records.
What AEMC® Instruments will do:Ifamalfunctionoccurswithintheone-yearperiod,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.
Digital Ground Resistance Tester Model 4620 and 4630 43
Notes:
03/10
99-MAN100259v12
Chauvin Arnoux®, Inc. d.b.a. AEMC® Instruments15FaradayDrive•Dover,NH03820USA•Phone:(603)749-6434•Fax:(603)742-2346
www.aemc.com