AEMC 4500 User manual

DIGITAL GROUND
RESISTANCE TESTER 4500
ENGLISH User Manual

Owner’s Record
The serial number for the Model 4500 is located on the front of the instru-
ment. Please record this number and purchase date for your records.
GROUND RESISTANCE TESTER MODEL 4500
CATALOG #: 450.100
SERIAL #: _______________________________________________
PURCHASE DATE: ________________________________________
DISTRIBUTOR: ___________________________________________

Table of Contents
1. INTRODUCTION ....................................................................3
1.1 International Electrical Symbols.....................................................4
1.2 Receiving Your Shipment...............................................................4
1.3 Ordering Information ......................................................................4
1.3.1 Accessories and Replacement Parts ................................4
2. PRODUCT FEATURES............................................................6
2.1 Description .....................................................................................6
2.2 Detaching the Cover ......................................................................7
2.3 Control Features ............................................................................8
3. SPECIFICATIONS ..................................................................9
3.1 ElectricalSpecications .................................................................9
3.2 Accuracy ......................................................................................10
3.3 TableofInuencingParameters .................................................. 11
3.4 InuenceofStrayVoltage ............................................................12
3.5 InuenceofAuxiliaryResistances ...............................................12
3.6 MechanicalSpecications............................................................13
3.7 SafetySpecications....................................................................14
4. OPERATION .........................................................................15
4.1 Grounding Electrode Resistance .................................................15
4.1.1 Effect of Electrode Size/Depth on Resistance.................17
4.1.2 Effects of Soil Resistivity on Electrode Resistance .........18
4.1.3 Factors Affecting Soil Resistivity......................................18
4.1.4 Effect of Ground Electrode Depth on Resistance............21
4.2 GroundResistanceValues ..........................................................22
4.3 Ground Resistance Testing Principle ...........................................24
4.3.1 PositionofAuxiliaryElectrodesinMeasurements.................25
4.4 Measuring Resistance of Ground Electrodes ..............................26
4.4.1 AuxiliaryElectrodeSpacing.............................................28
4.5 Ground Resistance Measurement Procedures............................29
4.5.1 Over-range Indication......................................................30
4.5.2 Incorrect Measurements..................................................30
4.6 2-Point Measurement (SimpliedMeasurement) .....................30

4.7 Continuity Measurement ..............................................................31
4.8 Soil Resistivity Measurements .....................................................32
4.9 Soil Resistivity Measurement Procedure (4-Point)................................33
4.10 Multiple Electrode System ...........................................................36
5. MAINTENANCE....................................................................38
5.1 Warning .......................................................................................38
5.2 Power Supply...............................................................................38
5.2.1 TestingBatteryVoltage....................................................38
5.2.2 Average Operating Time..................................................38
5.2.3 Recharging Built-In Battery .............................................39
5.2.4 PowerSupplyfromExternalBattery ...............................39
5.2.5 Replacing Battery ............................................................39
5.2.6 ChangingtheSupplyVoltage(110/220VAC)...................40
5.2.7 Replacing the Supply Fuse .............................................41
5.2.8 Replacing the Safety Fuse ..............................................41
5.3 Cleaning.......................................................................................42
5.4 Storage ........................................................................................42
Repair and Calibration..........................................................................43
Technical and Sales Assistance ...........................................................43
Limited Warranty...................................................................................44
Warranty Repairs..................................................................................44

Digital Ground Resistance Tester Model 4500 3
CHAPTER 1
INTRODUCTION
Warning
“It should be impressed on all personnel that a lethal potential can exist
between the station ground and a remote ground if a system fault involving
the station ground occurs while tests are being made. Since one of the
objects of tests on a station ground is the establishment of the location of
an effectively remote point for both current and potential electrodes, the
leads to the electrodes must be treated as though a possible potential
could exist between these test leads and any point on the station ground
grid.”
- excerpted from IEEE Std. 81-1962
These safety warnings are provided to ensure the safety of per-
sonnel and proper operation of the instrument.
• Theinstrumentmustnotbeoperatedbeyonditsspecied
operating range.
• Safetyistheresponsibilityoftheoperator.
• Allmetalobjectsorwiresconnectedtotheelectricalsystem
should be assumed to be lethal until tested. Grounding
systemsarenoexception.
• Useextremecautionwhenusingtheinstrumentaround
energized electrical equipment.
• Neverattempttousetheinstrumenttotwistorprythe
ground electrode or ground wire away from the equipment
being grounded.
• AEMC®Instruments considers the use of rubber gloves
tobeanexcellentsafetypracticeeveniftheequipmentis
properly operated and correctly grounded.
• Alwaysinspecttheinstrumentandleadspriortouse.
Replace any defective parts immediately.

4 Digital Ground Resistance Tester Model 4500
1.1 International Electrical Symbols
Thissymbolsigniesthattheinstrumentisprotectedbydoubleor
reinforced insulation. Use only specied replacement parts when
servicing the instrument.
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.
1.2 Receiving Your Shipment
Upon receiving your shipment, make sure that the contents are consistent
with the packing list. Notify your distributor of any missing items. If the equip-
mentappearstobedamaged,leaclaimimmediatelywiththecarrierand
notify your distributor at once, giving a detailed description of any damage.
Save the damaged packing container to substantiate your claim.
1.3 Ordering Information
Ground Resistance Tester Model 4500 ............................... Cat. #450.100
Includes AC power supply cord, 12V nickel-cadmium battery (installed), adhesive label (C1-
P1-P2-C2), hex key, spare fuse, and user manual.
1.3.1 Accessories and Replacement Parts
Test Kit for Model 4500...................................................................... Cat. #100.525
Includes Canvas Bag, [2] 500 ft Color-coded Leads on Reels, [1] 30 ft Color-coded Lead,
[2] T-shaped Auxiliary Ground Electrodes.
Test Kit for 3-Point Testing (Supplementalfor4-Pointtesting) ........ Cat. #2130.61
Includes Carrying Bag, [2] 100 ft Color-coded Leads, [1] 16 ft Lead and [2] 16" T-shaped
Auxiliary Ground Electrodes.
Battery–Replacement12VNiCD....................................... Cat. #2960.10
Fuse-Setof3,3.15A,250V,6x32mm(chargerboard)........ Cat. #100.357
Fuse–Setof5,0.1A,380V,6x32mm(measureboard)......... Cat. #2970.12

Digital Ground Resistance Tester Model 4500 5
Setof2,T-shapedAuxiliaryGroundElectrodes.................. Cat. #100.335
GroundTesterVideo/WorkbookSet ....................................Cat. #2130.64
25Ω Calibration Checker ..................................................... Cat. #2130.59
Tape Measure – AEMC 100 ft.............................................. Cat. #2130.60
NEW: Order Accessories and Replacement Parts Directly Online
Check our Storefront at www.aemc.com for availability

6 Digital Ground Resistance Tester Model 4500
CHAPTER 2
PRODUCT FEATURES
2.1 Description
The Digital Ground Resistance Tester Model 4500 is a rugged, easy-to-
usetesterwhichisspecicallydesignedformeasuringverylowresistance
onlargegroundingsystems(groundgrids,groundmats),evenunderdif-
cultconditionssuchashighstraycurrentsorexcessiveauxiliaryelectrode
resistance.
This high performance instrument is capable of measuring up to 20kΩ,
anddirect readingwitha resolutionof 1milliohmispossible.The extra
large 3½ digit LCD display minimizes the possibility of operator reading
error,anddualindicators(blinkingdisplayandarrow)warntheoperator
whenexcessstraycurrentorauxiliaryelectroderesistanceispresent,or
when there is a lack of continuity between leads and electrodes. A beeper
notiestheuserifavoltagegreaterthan20Vpeakispresentbetweenthe
terminals X and Y or X and Z when the ground leads are connected.
The Model 4500 can be used to perform soil resistivity measurements with
the four-point method by using the high 20kΩrange and is designed in a
sturdy, dust and water-resistant carrying case with a detachable cover.
Carrying
Handle
Snaps for Closing Cover
Protective Cover
Case for
Papers
Compartment
for Leads and
Hex Key
X
X
Z
Y
v
BATTERY
CHARGE
BLINKING DISPLAY
AND
POINTER INDICATE
EXCESSIVE
-TRANSIENTNOISE
-ELECTRODE
RESISTANCE
EXTERNAL
12V
TEST RANGE
TEST CURRENT
DIGITAL GROUND
RESISTANCE
TESTER
MODEL 4500
mA 210 50
ΩkΩ
220 200 220
50/60/400Hz_110V
!
BEEPER
INDICATES HIGH
GROUND VOLTAGE
AEMC
INSTRUMENTS
Figure 1

Digital Ground Resistance Tester Model 4500 7
2.2 Detaching the Cover
To detach the cover from the case, apply downward pressure to the rear
portionofthecoverwhilegrippingitrmly.
To re-attach the cover, t the hinges into the respective housings and
apply strong rear-to-front pressure to the cover until it snaps into place.
F
F
Unhinging
Supporting Point
Figure 2

8 Digital Ground Resistance Tester Model 4500
C2
P2
P1
C1
6
7 8 9 10
11
12
13
14
16
15
5
4
3
2
1
2.3 Control Features
1. Test button
2. InputTerminal(Z)-(C2)
3. InputTerminal(Y)-(P2)
4. InputTerminal(Xv)-(P1)
5. Shorting strip
6. InputTerminal(X)-(C1)
7. Incorrect measurement indicator
8. Low battery indicator
9. Display
10. Battery charge indicator
11. Supply voltage indicator
12. Jack for power supply cord
13. Connectingterminalsforpowersupplyfromexternalbattery
(12VDC)
14. Range selector switch
15. Test Current selector switch
16. Adhesivelabel(C-1,P-1,P-2,C-2)suppliedwitheachinstrument
Figure 3

Digital Ground Resistance Tester Model 4500 9
CHAPTER 3
SPECIFICATIONS
3.1 Electrical Specifications
Reference Conditions: 23°C±3K,30to50%RH;powersupply-12V±0.2V;noelectricalor
magneticeld,noauxiliaryrodresistance,nonoisevoltage.
NOTE: Specicationsgivenfor60Hzdistributionsystems;if50Hz,consultfactory.
2Ω
1mΩ
10mA or
50mA
20Ω
10mΩ
200Ω
0.1mΩ
2000Ω
1Ω
2mA or
10mA
20kΩ
10Ω
2mA or
10mA
Ranges
Resolution
Recommended
Current Ranges
2mA, 10mA,
or 50mA
Maximum Output Voltage: 38Vrms
Accuracy (see chart on following page):
±2% of Reading ± 1ct from 10% to 100% of range
Test Current Ranges: 2mA, 10mA, 50mA
Maximum Auxiliary Electrode Resistance:
Ry: 50kΩon 20Ω, 200Ω, 2000Ω, and
20kΩranges; 5kΩon 2Ωrange
Rz: 2mA range: 15kΩ
10mA range: 3000Ω
50mA range: 400Ω
Noise Inuence on Accuracy:
0.5%ofrange(max)to20Vpeak-to-peak(20xpeak)
Operating Frequency: 128Hz square wave
Dielectric Test:2000Vrms,50/60Hz betweenfourinterconnected mea-
suring terminals and any external metal ground between line input and
measuring terminals on front panel.
Power Supply:Onebuilt-inrechargeable12Vbattery,orexternal12VDC
Battery Life:
4hrson50mAtestcurrent(80015-secondmeasurements)
7hrson2mAand10mAtestcurrents(150015-secondmeasurements)

10 Digital Ground Resistance Tester Model 4500
Charging Time: 14 hours typical
Charging Supply Voltage:Internallyselectable110/220V,45to450Hz
Low Battery Indication: Battery can be recharged with built-in dual volt-
agechargingunit:94to127Vor187to253V(47to450Hz).
WARNING: Do not fully discharge batteries.
Fuse Protection: 250Vrms(measurementcircuit)via3.15A250Vfuse
3.2 Accuracy
Range ResolutionTest
Current
Accuracy
in % of
Reading
* Maximum Value of
Y and Z Electrodes
Having Influence < 1%
Ry Rz
2Ω
2 mA
± 5mΩ± 1ct
± 2% ± 1ct
± 2% ± 1ct
of 10% to 100%
of full scale
5kΩ
10kΩ
± 2% ± 30mΩ± 1ct
± 2% ± 3mΩ± 1ct
0 to
0.2Ω
0.2Ω
to 2Ω
1mΩ
1mΩ
10mΩ
0.1Ω
1Ω
10Ω20kΩ
2kΩ
200Ω
20Ω
600Ω
to 20kΩ
to be
selected
in relation
to the test
current
10mA
50mA
2mA
10mA
50mA
2mA
10mA
50mA
2mA
10mA
50mA
2mA
10mA
50mA*
2mA*
10mA*
50mA*
No accuracy specification - do not use
* See Table III for maximum auxiliary resistance
5kΩ
5kΩ

Digital Ground Resistance Tester Model 4500 11
3.3 Table of Influencing Parameters
Supply Voltage
Temperature
Auxiliary
Electrode
Resistance (Ry)
Influence of
Auxiliary
Electrode
Resistance (Rz)
in Relation to
Test Current
DC Voltage in
Series with Rx
AC 60 Hz Stray
Voltage Influence
in Series with
Rx, Ry or Rz
Reference
Conditions
12V ±0.2V 11 to 14V DC
73˚F ±37˚F23˚F to 122˚F
23˚C ±3˚C -5˚C to 50˚C
±0.5%/50˚F
(3)
±0.5%/10˚C
0.2%/volt 0.3%/volt
±1%/50˚F
(3)
Ry = 00to 50kΩ
(1)
N/A
N/A See Table 3
N/A0 to 20V DC
(2)
Rz = 0 See Table 3
0.5% /10kΩ
(1)
2mA: 0.1%/10kΩ
10mA: 0.1%/3kΩ
50mA: 0.1%/1kΩ
2mA: 0.3%/10kΩ
10mA: 0.3%/3kΩ
50mA: 0.3%/1kΩ
or 5 cts
1% /10kΩ
(1)
±1%/10˚C
Operating
Conditions
% of Measurement
Typical Maximum
Parameters
Table 1
1. For the 2Ω range (2mA and 10mA test currents), maximum Ry is
5kΩ. Inuence will typically be 0.5%/5kΩ, with a maximum of 1%
max/5kΩor 3cts.
2. Presenceof DCvoltage maytendtolimitthemaximum(Rx+Rz)
level indicated within Table 3.
3. From 10% to 100% of measuring scale interval. It is necessary to add
the following quantities to those indicated with Table 1:
± 10mΩfor 2Ω/2mA range
± 3mΩfor 2Ω/10mA range
± 1 count for other ranges

12 Digital Ground Resistance Tester Model 4500
3.4 Influence of Stray Voltage
2 20 200 2 k 20 k
2 mA
10 mA
50 mA
ΩΩ Range
Test
Current
Table 2
Shaded areas indicate the ranges in which measurements can be
performed, where 40V, 50/60Hz peak-to-peak stray voltage is present,
without obtaining error levels representing more than 0.5% of the
measurement range.
3.5 Influence of Auxiliary Resistances
Intheabsenceofstraysignals,themaximumvaluesfor(Rx+Rz)whichwill
allow measurements to be performed, are those indicated within Table 3.
Range
Current
50 mA
10 mA
2 mA
(*)
Rx + Rz = 600Ω max
Rx + Rz = 4000Ω max
Rx + Rz = 20 kΩ max
2Ω20 Ω200Ω2 k
Ω20 kΩ
(*)
(*)
Do not use
Table 3
*EvenifauxiliaryresistanceofRz=0,themaximumreadingis<2000-countsonthesethree
ranges(voltagelimitingcircuitatoutputterminals).

Digital Ground Resistance Tester Model 4500 13
Table4showsthemaximumresistanceofthecurrentcircuit(Rx+Rz)for
strayvoltageof10Vpeak-to-peak.
Range
Current
50 mA
10 mA
2 mA
Rx + Rz = 400Ωmax
Rx + Rz = 3000Ωmax
Rx + Rz = 15 kΩmax
2Ω20 Ω200Ω2 k
Ω20 kΩ
Do not use
Table 4
3.6 Mechanical Specifications
Display:
2000-count,7segmentLCD,.71"(3-1/2digit)
Connection:
Viaterminals(wires;forkedlugswithmingapof6mm)bananajackswith
Ø 4mm
Operating Temperature:
14°to122°F(-10°to50°C)
Case:
Heavy-duty plastic, with detachable cover and carrying handle
Colors:
Case - Safety yellow; Front Panel - Brown
Dimensions:
15.75x10.2x9.8"(400x260x250mm)
Weight:
14lbs(6.5kg)approximate

14 Digital Ground Resistance Tester Model 4500
3.7 Safety Specifications
Impact Resistance:
Shock and vibration according to MIL-T-28800D class 3
Environmental:
O-ring sealed faceplate against water and dust, sealed cover when closed;
IEC529, DIN 0470-T1
EN61010-1+A2(ed.95)
Double Insulation
30V,Cat.IIformeasurement
230V,Cat.IIforbatterycharger
12V,Cat.IIforauxiliarysupply
EN 61557
Electromagnetic Compatibility:
EmmissionandImmunity:IEC61326-1(ed.98)

Digital Ground Resistance Tester Model 4500 15
CHAPTER 4
OPERATION
4.1 Grounding Electrode Resistance
Figure 4 illustrates a grounding rod. The resistance of the electrode has
the following components:
• theresistanceofthemetalandthatoftheconnectiontoit
• thecontactresistanceofthesurroundingearthtotheelectrode
• theresistanceinthesurroundingearth
Morespecically:
A) Groundingelectrodesareusuallymadeofaveryconductivemetal
(copper)withadequatecrosssectionssothatoverallresistanceis
negligible.
B) TheNationalInstituteofStandardandTechnology(N.I.S.T.)has
demonstrated that the resistance between the electrode and the
surrounding earth is negligible if the electrode is free of paint,
greaseorothercoating,andiftheearthisrmlypacked.
Ground Rod
and Clamp
Contact
Resistance
Between Rod
and Soil
Concentric
Shells of
Earth
Figure 4

16 Digital Ground Resistance Tester Model 4500
C) Theonlycomponentremainingistheresistanceofthesurround-
ing earth. The electrode can be thought of as being surrounded
by concentric shells of earth or soil, all of the same thickness. The
closer the shell to the electrode, the smaller its surface; hence,
the greater its resistance. The farther away the shells are from the
electrode, the greater the surface of the shell; hence, the lower
the resistance. Eventually, adding shells at a distance from the
grounding electrode will no longer noticeably affect the overall
earth resistance surrounding the electrode. The distance at which
this effect occurs is referred to as the effective resistance area and
is directly dependent on the depth of the grounding electrode.
In theory, the ground resistance may be derived from the general for-
mula:
R=ρResistance=Resistivityx
L
A
Length
Area
This formula clearly illustrates why the shells of concentric earth decrease
in resistance the farther they are from the ground rod:
R=ResistivityofSoilx Thickness of Shell
Area
Inthecaseofgroundresistance,uniformearth(orsoil)resistivitythrough-
out the volume is assumed, although this is seldom the case in nature.
The equations for systems of electrodes are very complex and often
expressedonlyasapproximations.Themostcommonlyusedformulafor
single ground electrode systems, developed by Professor H. R. Dwight of
the Massachusetts Institute of Technology, follows:
R= ρ
2πL
{(In4L)-1}
r
R=resistanceinohmsofthegroundrodtotheearth(orsoil)
L=groundingelectrodelength
r=groundingelectroderadius
ρ=averageresistivityinohms-cm

Digital Ground Resistance Tester Model 4500 17
4.1.1 Effect of Ground Electrode Size and Depth on
Resistance
Size: Increasing the diameter of the rod does not materially reduce its
resistance. Doubling the diameter reduces resistance by less than 10%.
0
25
50
75
100
1/2 5/8 3/4 111/4 1 1/2
1 3/4
Rod Diameter (inches)
Resistance in %
Figure 5
Depth: As a ground rod is driven deeper into the earth, its resistance
is substantially reduced. In general, doubling the rod length reduces the
resistance by an additional 40%.
515253540506
070
1
2
3
4
5
6
8
10
20
30
40
60
80
100
200
Driven Depth in Feet
Ground Resistance Versus Ground Rod Depth
Resistance in Ohms
1/2" dia.1" dia.
Figure 6

18 Digital Ground Resistance Tester Model 4500
NEC®2014250.52(A)(5)requiresaminimumof8ft(2.4m)oftheelec-
trode to be in contact with the soil. The most common of electrode is a
10ft(3m)cylindricalrodwhichmeetstheNEC®code, which requires a
minimumdiameterof5/8”(1.59cm).
4.1.2 Effects of Soil Resistivity on Ground Electrode
Resistance
Dwight’s formula, cited previously, shows that the resistance to earth of
grounding electrodes depends not only on the depth and surface area of
grounding electrodes but on soil resistivity as well. Soil resistivity is the key
factor that determines what the resistance of a grounding electrode will be,
and to what depth it must be driven to obtain low ground resistance. The
resistivity of the soil varies widely throughout the world and changes sea-
sonally. Soil resistivity is determined largely by its content of electrolytes,
consisting of moisture, minerals and dissolved salts. A dry soil has high
resistivity if it contains no soluble salts.
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
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 5
4.1.3 Factors Affecting Soil Resistivity
Two samples of soil, when thoroughly dried, may become in fact very good
insulators, having a resistivity in excess of 109 ohm-centimeters. The
resistivityofthesoilsampleisseentochangequiterapidlyuntilapproxi-
mately twenty percent or greater moisture content is reached.