MEGOHMMETER
1210N
1250N
ENGLISH User Manual
V
500V
1kV
x 10
300
0
100
200
400
500
600
20
15
30
40
50
100
200
500
50
20
10
5
4
3
2
1.5
10
1
(1kV)
(250V)
(500V)
MΩ
MEGOHMMETER
Model 1250N
INSTRUMENTS
®
600V CAT II / 1000V CAT I
!
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 #: 1326.01 / 1326.02
Model #: 1210 / 1250
Please fill in the appropriate date as indicated:
Date Received: _________________________________
Date Calibration Due: _______________________
Chauvin Arnoux®, Inc.
d.b.a AEMC® Instruments
www.aemc.com
Table of Contents
1. INTRODUCTION ...................................................................3
1.1 International Electrical Symbols .....................................................3
1.2 DenitionofMeasurementCategories ...........................................4
1.3 ReceivingYourShipment ...............................................................4
1.4 OrderingInformation ......................................................................4
1.4.1 AccessoriesandReplacementParts ................................4
2. PRODUCT FEATURES ..........................................................5
2.1 Description .....................................................................................5
2.2 Model1210NFeatures ..................................................................6
2.3 Model1250NFeatures ..................................................................6
2.4 Model1210NControlFeatures ......................................................7
2.5 Model1250NControlFeatures ......................................................8
2.6 1210Nand1250NControlFeatures ..............................................9
3. SPECIFICATIONS ...............................................................10
3.1 Model1210NSpecications ........................................................10
3.1.1 ElectricalSpecications ...................................................10
3.1.2 MechanicalSpecications ...............................................11
3.1.3 SafetySpecications ....................................................... 11
3.2 Model1250NSpecications ........................................................12
3.2.1 ElectricalSpecications ...................................................12
3.2.2 MechanicalSpecications ...............................................12
3.2.3 SafetySpecications .......................................................13
4. OPERATION .......................................................................14
4.1 UsingtheModel1210N ...............................................................14
4.1.1 InstrumentGroundTerminal ............................................14
4.1.2 Auto-ranging ....................................................................14
4.1.3 SafetyCheck-VoltageTest ...........................................14
4.1.4 InsulationResistanceTesting(MΩRange) .....................14
4.1.5 SuccessfulInsulationResistanceTesting ........................16
4.1.6 InsulationMeasurement—Connections ........................16
4.1.7 InsulationResistanceMeasurementsonMotors ............19
2
MegohmmeterModels1210N/1250N
4.2 UsingtheModel1250N ...............................................................21
4.2.1 InstrumentGroundTerminal ............................................21
4.2.2 Auto-ranging ....................................................................21
4.2.3 SafetyCheck-VoltageTest ...........................................21
4.2.4 UtilizationoftheGuardTerminal .....................................21
4.2.5 InsulationResistanceTesting(MΩRange) .....................23
4.2.6 SuccessfulInsulationResistanceTesting ........................25
4.2.7 InsulationMeasurement-Connections ...........................25
4.2.8 InsulationResistanceMeasurementsonMotors ............28
5. MAINTENANCE ..................................................................30
5.1 Warning .......................................................................................30
5.2 Cleaning .......................................................................................30
RepairandCalibration .................................................................................31
TechnicalandSalesAssistance ..................................................................31
Limited Warranty .........................................................................................32
WarrantyRepairs .........................................................................................32
MegohmmeterModels1210N/1250N
3
CHAPTER 1
INTRODUCTION
Warning
Thesesafetywarningsareprovidedtoensurethesafetyofpersonnel
andproperoperationoftheinstrument.
• Readtheinstructionmanualcompletelyandfollowallsafety
informationbeforeoperatingthisinstrument.
• Safetyistheresponsibilityoftheoperator!
• Testsaretobecarriedoutonlyondeadcircuits!Checkforlive
circuitsbeforemakingresistancemeasurements(safetycheck).
• TheMegohmmeterModels1210N/1250Naresourcesofhigh
voltage,asisthesampleconnectedtothem.Allpersonsperform-
ingorassistinginthetestsmustemployallsafetyprecautionsto
preventelectricalshocktothemselvesandtoothers.
• AEMC
®
Instrumentsconsiderstheuseofrubberglovestobe
anexcellentsafetypracticeeveniftheequipmentisproperly
operatedandcorrectlygrounded.
• Whentestingcapacitancesamples,makesurethattheyhave
beenproperlydischargedandthattheyaresafetotouch.
Dielectricinsulationsamplesshouldbeshort-circuitedforatleast
vetimestheamountoftimetheywereenergized.
• Usetheleadssuppliedwiththemegohmmeter.Ifdefectiveor
used,replacebeforetesting.
1.1 International Electrical Symbols
Thissymbolsigniesthattheinstrumentisprotectedbydoubleorrein-
forced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.
4
MegohmmeterModels1210N/1250N
1.2 DenitionofMeasurementCategories
Cat. I: Formeasurementsoncircuits not directlyconnectedtotheAC
supply wall outlet such as protected secondaries, signal level,
andlimitedenergycircuits.
Cat. II: For measurements performed on circuits directly connected to
the electrical distribution system. Examples are measurements
onhouseholdappliancesorportabletools.
Cat. III: For measurements performed in the building installation at
the distribution level such as on hardwired equipment in xed
installationandcircuitbreakers.
Cat. IV: For measurements performed at the primary electrical supply
(<1000V) such as on primary overcurrent protection devices,
ripplecontrolunits,ormeters.
1.3 ReceivingYourShipment
Uponreceivingyourshipment,makesurethatthecontentsareconsistent
with the packing list. Notify your distributor of any missing items. If the
equipmentappearstobedamaged,leaclaimimmediatelywiththecar-
rierandnotifyyourdistributoratonce,givingadetaileddescriptionofany
damage.Savethedamagedpackingcontainertosubstantiateyourclaim.
Donotuseaninstrumentthatappearstobedamaged.
1.4 Ordering Information
Megohmmeter Model 1210N ............................................. Cat. #1326.01
Megohmmeter Model 1250N ............................................. Cat. #1326.02
Both models include a carrying strap with lead pouch, three color-coded leads, ground lead,
two insulated alligator clips, test probe and user manual.
1.4.1 Accessories and Replacement Parts
Setof10fuses,0.2A,250Vfast-blow5x20mm................... Cat. #2973.02
Leadpouchwiththreecolor-codedsafetyleads,
groundlead,twosafetyalligatorclipsandtestprobe.......... Cat. #1019.01
Leadpouchwiththreecolor-codedleads,
groundlead,twoalligatorclips,andtestprobe ................... Cat. #1017.56
MegohmmeterModels1210N/1250N
5
CHAPTER 2
PRODUCT FEATURES
2.1 Description
TheAEMC®Models1210Nand1250Narecompact,self-containedhand-
crankedmegohmmeters.Theyarepracticalanddependableinstruments
designedfora broadrangeofplantandeldserviceapplications,such
as acceptance testing and preventive maintenance of wiring, cables,
switchgear, and motors. The easy hand-cranked operation provides a
steadyrectiedDCvoltageoutputacrosstheentirerangeforconsistently
reliablereadings.
These megohmmeters incorporate a built-in, sealed alternator and a
constant DC voltage circuit to provide a stable output and give direct
insulationresistancereading.
They are ruggedly built and use an O-ring-sealed, cast aluminum case
withapolycarbonatefrontpaneldesignedforharsh,heavy-dutyuseand
protectionagainstdustandwater.
The Models 1210N/1250N have a unique auto-ranging feature which
expandsthescalebyx10andalmostdoublesthescalelength.Whenthe
pointerreachesneartheendofscale,theauto-rangingfeatureactivates,
returningthepointertothebeginningofthescalewiththex10redLED
indicator on.
Insulation resistance is indicated with a rugged taut-band meter move-
mentonalogarithmicscale.Theindicatorscaleiseasytoread.
6
MegohmmeterModels1210N/1250N
2.2 Model1210NFeatures
• Measuresinsulationat500V,resistance,continuity
• Testvoltageconstantacrosstheentiremeasurementrange
• AutorangingMΩ,kΩandΩranges
• Designedforharshenvironments:offshore,mining,heavy-duty
eld,industrial,andmilitaryuse
• Extraruggedcastaluminumcase;O-ringsealedagainstrain,
water,anddust;aluminumlid
• Compact,self-containedpackage;foldingcrank
• Largedirect-readingscale
• 600Vtestvoltagerange(safetycheck)
2.3 Model1250NFeatures
• Threetestvoltages:250,500,1000V
• Testvoltageconstantacrosstheentiremeasurementrange
• AutorangingMΩranges
• Designedforharshenvironments:offshore,mining,heavy-duty
eld,industrial,andmilitaryuse
• Extraruggedcastaluminumcase;O-ringsealedagainstrain,
water,anddust;aluminumlid
• Compact,self-containedpackage,foldingcrank
• Fourterminalsincludingguardandground
• Largedirect-readingscale
• 600Vtestvoltagerange(safetycheck)
MegohmmeterModels1210N/1250N
7
2.4 Model1210NControlFeatures
kΩ
Ω
M
V
x 10
5
0
1
2
6
7
10
V
FUS
1
2
3
4
5
10
20
10
20
30
0.5
50
(500V)
(1mA)
(5mA)
ΜΩ
2!C
42
300
0
100
200
400
500
600
Ω
κΩ
4
3
8
9
40
0
Ω
MEGOHMMETER
Model 1210N
INSTRUMENTS
®
600V CAT II / 1000V CAT I !
123
4
5
6
7
8
9
10
Figure 1
1. Line(-)terminalBlack
2. Fuse0.2A
3. Earth(+)terminalRed
4. Instrumentgroundterminalforusersafety
5. AmberLEDilluminateswhenpropercrankspeedisattained,
indicatingpresenceofselectedoutput
6. Foldawayhandle
7. Mechanicalzeroadjustmentscrew
8. Rangeswitch-safetytestrstonMΩ/Vrangeto500VAC
9. Autoranging:RedLEDilluminateswhenreadingneedstobe
multipliedx10toobtainthetruevalue(MΩ,kΩ,Ωranges)
10. Securityngerrestisolatesusershandfromterminalswhilegivinga
rmgripduringanoperation
8
MegohmmeterModels1210N/1250N
2.5 Model1250NControlFeatures
V
500V
1kV
250V
x 10
300
0
100
200
400
500
600
V
G
20
15
30
40
50
100
200
500
50
20
10
5
4
3
2
1.5
10
1
(1kV)
(250V)
(500V)
ΜΩ
2!C
42
MEGOHMMETER
Model 1250N
INSTRUMENTS
®
600V CAT II / 1000V CAT I !
123
4
5
6
7
8
9
10
Figure 1-A
1. Line(-)terminal-Black
2. Guardterminal-Blue
3. Earth(+)terminal-Red
4. Instrumentgroundterminalforusersafety
5. GreenLEDilluminateswhenpropercrankspeedisattained,
indicatingpresenceofselectedtestvoltage
6. Foldawayhandle
7. Mechanicalzeroadjustmentscrew
8. Rangeswitch-Safetytestrston500V/V~rangeto500VAC
9. Autoranging:RedLEDilluminateswhenreadingneedstobe
multipliedx10toobtainthetruevalue(MΩrange)
10. Securityngerrestisolatesusershandfromterminalswhilegivinga
rmgripduringanoperation
MegohmmeterModels1210N/1250N
9
2.6 1210Nand1250NControlFeatures
11.Long,sturdyassembly
boltsfortightcase
closing.
12. Instrumentground
terminalforenhanced
usersafety.
13. Ruggedtaut-band
meter movement.
14.Switchslideassembly.
15. Alternatorcrankshaft,
gearsandbearings
permanentlylubricated
and sealed.
16.Foldawaycrank.
17.Diecastaluminum
case(covernot
shown).
18.O-ringconstruction
sealsoutdirtand
water.
19.Simpleprintedcircuit
boardassemblyfor
easy calibration and
maintenance.
20.Highimpactpolycar-
bonatefaceplate.
Figure 2
12
13
14
15
16
17
18
19
20
11
10
MegohmmeterModels1210N/1250N
CHAPTER 3
SPECIFICATIONS
3.1 Model1210NSpecications
3.1.1 ElectricalSpecications
INSULATION TESTS
DC Test Voltage: 500V
(testvoltagegeneratedinfullacrosstheentiremeasurementrange)
Megohm Range (Auto-ranging): 0.5 to 5.5MΩ;5.5to200MΩ
Short Circuit Current: 5mA(max)
Accuracy:2.5%offullscalelength
Charging Time: 0.5s/µF
Discharging Time (Auto): 5s/µF
RESISTANCE TESTS
DC Test Current:1mAconstant,600Vmax
Kilohm Range (Auto-ranging): 0to45kΩ;45to500kΩ
Accuracy: 2.5%fullscalelength
Charging Time: 0.5s/µF
Discharging Time (Auto): 5s/µF
CONTINUITY TESTS
DC Test Current: 5mAconstant,10Vmax
Ohm Range (Auto-ranging): 0 to 9Ω;9to100Ω
Accuracy: 2%offullscalelength
Fuse Protection: 0.2A,250V,fast-blow,5x20mm
VOLTAGE TESTS (Safety Check):
Voltage Range: 0to600VAC
Frequency: 45 to 450Hz
Accuracy: 3%offullscale
Input Impedance: 100kΩ(approx)
MegohmmeterModels1210N/1250N
11
3.1.2 MechanicalSpecications
Test Voltage Indicator:
AmberLEDindicatespropertestvoltageandcrankspeed
Scale: Directreadingsonallranges;3"(76mm),blackonwhite
Autorange Indicator:
RedLEDindicatesAuto-range;multiplyresistancereadingsx10
Power Supply:
Hand-cranked,heavydutybrushlessalternatorandsolidstaterectica-
tionandamplicationforstablevoltage;testvoltagereachedat140rpm
(approx)
Dielectric Test: 2000V50/60Hz,between(-),(+),andgroundterminals
Meter Movement: Ruggedtautbandsuspension
Dimensions: 4.7x4.7x5.1"(120x120x130mm)
Weight: 3.3lbs(1.5kg)
Temperature Range:
Reference range:64to75°F(18to24°C),30-50%RH
Operating range:14to122°F(-10to50°C),0-80%RH
Storage range:-4to176°F(-20to80°C),0-90%RH
Case:
Castaluminumalloycaseandlidpaintedsafetyyellow,withheavyduty
graypolycarbonatefrontpanel;O-ringsealbetweenfrontpaneland
case;sealedagainstwateranddust;foldingcrank
Terminals:
“+”Line(red);“-”earth(black);acceptsstandard4mmsafetybanana
plugs;groundaccepts4mmbananaplugorspadelugs
3.1.3 SafetySpecications
Sealed: IP54withlid,IP52withoutlid
Insulation Tester:VDE413part1/4exceptf
Safety:IEC1010-1;600VCATII;1000VCATI
Envelope Protection: IEC529
Vibration: MIL-T-38800D
Shock: IEC51
12
MegohmmeterModels1210N/1250N
3.2 Model1250NSpecications
3.2.1 ElectricalSpecications
INSULATION TESTS
DC Test Voltages: 250,500,1000V
(Testvoltagesgeneratedinfullacrosstheentiremeasurementrange)
Megohm Ranges (Auto-ranging):
250V: 1to11MΩ
11 to 500MΩ
500V: 1to11MΩ
11 to 500MΩ
1000V: 10to110MΩ
110 to 5000MΩ
Short Circuit Current:5mA(approx)
Accuracy:2%offullscalelength
Charging Time: 250V:0.2s/µF
500V:0.5s/µF
1000V:0.5s/µF
Discharging Time (Auto): 8s/µF
VOLTAGE TESTS (Safety Check)
Voltage Range:0to600VAC
Accuracy:3%offullscale
3.2.2 MechanicalSpecications
Test Voltage Indicator:
GreenLEDindicatespropertestvoltageandcrankspeed
Warning: IfthecrankspeedLEDisnotONduringtest-
ing,thereadingisnotvalid.
Scale:Directreadingsonallranges;3"(76mm),blackonwhite
MegohmmeterModels1210N/1250N
13
Autorange Indicator:
RedLEDindicatesautorange;multiplyresistancereadingsx10
Dielectric Test:
2000V50/60Hz,between(-),(+),guardandgroundterminals
Power Supply:
Hand-cranked,heavydutybrushlessalternatorandsolid state rectica-
tionandamplicationforstablevoltage;testvoltagereachedat140rpm
(approx)
Meter Movement:Ruggedtautbandsuspension
Dimensions: 4.7x4.7x5.1"(120x120x130mm)
Weight: 3.3lbs(1.5kg)
Temperature Range:
Reference range: 64to75°F(18to24°C),30-50%RH
Operating range: 14to122°F(-10to50°C),0-80%RH
Storage range: -4to176°F(-20to80°C),0-90%RH
Case:
Castaluminumalloycaseandlidpaintedsafetyyellow,withheavyduty
graypolycarbonatefrontpanel;O-ringsealbetweenfrontpanelandcase;
sealedagainstwateranddust;foldingcrank
Terminals:
“+”Line(red);“-”earth(black);“G”guard(blue);acceptssafety4mm
bananaplugs;groundaccepts4mmbananaplugsorspadelug
3.2.3 SafetySpecications
Sealed:IP54withlid,IP52withoutlid
Insulation Tester: VDE413part1/4exceptf
Safety: IEC1010-1;600VCATII;1000VCATI
Envelope Protection:IEC529
Vibration: MIL-T-38800D
Shock: IEC51
*All specications are subject to change without notice
14
MegohmmeterModels1210N/1250N
CHAPTER 4
OPERATION
4.1 UsingtheModel1210N
4.1.1 Instrument Ground Terminal
TheMegohmmeterModel1210Nisequippedwithaninstrumentground
terminalforenhancedusersafety.Groundyourinstrumentwheninuse.
4.1.2 Auto-ranging
How it works:Whenthe pointerreachesapproximately 90%ofthe full
scale length, the auto-range is triggered, the red auto-range (x10) LED
lightsup.Thepointergoesbacktothebeginningofthescaleandresumes
itstravel.Thereadingsshouldbemultipliedby10whenthex10LEDis
on.
4.1.3 Safety Check - Voltage Test
Before measuring insulation resistance, conrm that the sample is fully
discharged (particularly in dielectric and capacitance samples) and that
thesampleisnotconnectedtoanenergizedcircuit.
Toperformthevoltagetest,settherangeselectiontoV(MΩ),connectand
readontheredvoltagescale(600VACmax).DO NOT CRANK.Ifmeasur-
ingonaDCcircuit,thepointerwilldeectbutthemeasurementmaybe
inaccurate.
4.1.4 Insulation Resistance Testing (MΩ Range)
Aftercheckingforalivecircuit(seeSafetyCheckabove),selecttheMΩ
rangeandconnectthemegohmmeter.Severalconnectionexamplesare
illustrated further. Crank the handle until the amber LED on the upper
right-handsidelights,ensuringappropriatetestvoltageattheoutput.
MegohmmeterModels1210N/1250N
15
SPOT TESTING
Asageneralruleinspottesting,testvoltageshouldbeapplieduntilno
variationinreadingisnotedfor15secondsorappliedforaxed60sec-
onds.Oncapacitancecircuits,crankingforuptoaminuteormoremay
benecessarytofullychargethesample.Whatminimumvalueshouldbe
measured?TheIEEEstandardN°43-2000statesthatitisimpossibleto
specifythevalueofinsulationresistanceatwhichawindingwillfailelectri-
cally,butonmotors,minimumreadingsgenerallystatedare:
Rated Voltage R minimum
250 or less 2 MΩ
460 2 MΩ
Thereisnoxedgurefordeterminingwhatisgoodandbadinresistance
readings,buta goodguidewouldbe1 megohmforeveryonehundred
appliedoperatingvolts,asaminimumgure.Thisappliestomotorsand
transformers.Whentheinsulationresistancegets this low, an electrical
break-down can be expected at any time and rewinding or replacing
shouldbeconsidered.
Itisnotunusualfora winding to be 10 to100timestherecommended
minimum value (IEEE standard 43-2000: Recommended Practice for
Testing Insulation Resistance of Rotating Machinery),butthisvarieswith
temperatureandhumidity.
RATIO TESTING
Intimeresistancereading(DielectricAbsorptionRatio),readingsaretaken
at30secondsand60secondstoobtainthedielectricabsorptionratio.
Insulationresistance@60s
Insulationresistance@30s
Thistestisusefultoincreasetheaccuracyofspottesting.Ingeneral,a
ratioof1.25:2orbettershouldberequired.Aratiobelowthisindicatesthat
repairisprobablyneeded.
RememberthataDCinsulationtestmaybeusedforacceptancetesting,
butismorecommonlyusedtocheckthegradualdeteriorationofequip-
mentoveritslife.Consultyourequipmentmanufacturerforspecictestor
testvoltageifnotknown.
Insulationresistancedecreaseswithmoisture,temperatureandageand
shouldberecordedovertimeatagiventemperatureandcorrected.
=DielectricAbsorptionratio(DAR)
16
MegohmmeterModels1210N/1250N
4.1.5 Successful Insulation Resistance Testing
• Check with the equipment manufacturer for factory insulation resis-
tancereadings.
• Donotrelyoninsulationresistancetestingaloneasproofofwinding
conditions.
• Donotexpectthesamevalueforallpartsofallmachines.
• Observe consistent test time duration, recognizing that total current
throughinsulationundertestwillvarywithtime.
• Correctallreadingsproperlytoastandardreferencetemperature(see
IEEEstd#43-2000,Temperature Correction Curve).
• Knowwhatyouaretesting.Isolatethepieceofequipmentfromother
circuitry.
• Watchtrendsratherthanrelyingonsingle“spot”readings.
4.1.6 Insulation Measurement — Connections
Figure3showstheconnectionstomeasuretheinsulationofoneconduc-
tor to the other conductors. The cable should be disconnected at both
endstoavoidleakagethroughswitchboardsandpanels.
Cable Insulation
Conductor Under Test
Fus
Figure 3
MegohmmeterModels1210N/1250N
17
Figures4and5showtheconnectionsfortestinginsulationfromasupply
conductortoground(motorframe).
Cable Insulation
Conductor Under Test
Fus
Figure 4
Fus
Cable Insulation
Conductor Under Test
Figure 5
Figure6showstheconnectionstoatransformer(lightingordistribution).
Make sure that the switches and/or circuit breakers on both sides are
open.Checkthehighvoltagewindingtoground,lowvoltagetoground,
andtheresistancebetweenthemwithnowindingground.
18
MegohmmeterModels1210N/1250N
Tested Winding
Transformer
Grounding Lug
Fus
Figure 6
Figure7showstheconnectionsformeasuringtheinsulationofathree-
phase line to ground by connecting the jumpers between phases. This
givesareadingofallconductorsatonce.Ifaloadsuchasamotor,heater,
etc.,isattachedtotheotherendoftheline,itwillreadtheloadresistance
togroundat thesametime.Byremoving thejumpers,readingscanbe
madebetweentheindividualconductorsandground.
Figure 7
MegohmmeterModels1210N/1250N
19
4.1.7 Insulation Resistance Measurements on Motors
Figure8showsreadingtheresistancetogroundofathree-phasemotor
winding.Sincethethree-phasemotorsareinternallyconnected,itisonly
necessarytoconnectoneleadtothemotorleadandtheotherleadtothe
motorframeasshown.
Fus
Figure 8
Figure9 shows the windingsofa three-phase motor separated.Some-
timesthiscanbedoneatthe lead terminals, while other times the end
bellsmustberemovedtogetattheleadwiresofthecoils.Byconnecting
themegohmmeterasshown,the phase insulation resistancevaluecan
nowbedetermined.Readbetweenphases“A”and“B”,then“B”and“C”,
then“C”and“A”.
A
B
C
Fus
Figure 9
20
MegohmmeterModels1210N/1250N
Figure10showsconnectionsfortestinginsulationfromasupplyconduc-
torinaswitchboxtoground(motorframe).Anidenticaltestmaybecarried
outfromthemotorstarter.
Motor Side of Switch:
Connection to One Leg
Grounded
Motor Frame
Starter In
Fus
Figure 10
MegohmmeterModels1210N/1250N
21
4.2 UsingtheModel1250N
4.2.1 Instrument Ground Terminal
TheMegohmmeterModel1250Nisequippedwithaninstrumentground
terminalforenhancedusersafety.Groundyourinstrumentwheninuse.
4.2.2 Auto-ranging
How it works: When the pointer reaches approximately 90% of the full
scale length, the auto-range is triggered, the red auto-range (x10) LED
lightsup.Thepointergoesbacktothebeginningofthescaleandresumes
itstravel.Thereadingsshouldbemultipliedby10whenthex10LEDison.
4.2.3 Safety Check - Voltage Test
Before measuring insulation resistance, conrm that the sample is fully
discharged (particularly in dielectric and capacitance samples) and that
thesampleisnotconnectedtoanenergizedcircuit.
Toperformthevoltagetest,settherangeselectionto500V,connectand
readontheredvoltagescale(600VACmax).DO NOT CRANK.Ifmeasur-
ingonaDCcircuit,thepointerwilldeectbutthemeasurementmaybe
inaccurate.
4.2.4 Utilization of the Guard Terminal
G
A
E
B
C
E = Exposed surface
A = Insulation
B = Shield
C = Conductor
Figure 13
22
MegohmmeterModels1210N/1250N
Guardterminalsareusefulwhenmeasuring highresistancevaluesand
forstabilizingreadings.
When testing the insulation at the end of a cable, it is necessary to
eliminatetheerrorfromsurfaceleakagewhichoccurs,particularlyathigh
resistancevalues.Thepurposeoftheguardterminalistoprovideathird
terminalwithinthepathofthesurfaceleakage“E”.Connecttheinstrument
asshowninFigure13.
Ifthereisnoshieldat“B”,useacopperwirewoundseveraltimesaround
theexposedsurface“B”.(Note:Ifashieldisnotavailableandyoudonot
makeupashieldaround“B”and connect to the guard terminal (-), the
measurementwillbeerroneousandleadtoconfusion as to the cable’s
state.)
Iftheguardterminalisnotconnectedat“B”,theinstrumentmeasuresthe
current “I” owing through the insulation and a surface leakage current
“i1”.SeeFigure14.
To EARTH
terminal
I
To LINE
terminal
NO CONNECTION
to Guard terminal
A
B
C
Ry
Rx
Rz
Rx: resistance through insulation
Ry: surface resistance
Rz: surface resistance
i1
Figure 14
MegohmmeterModels1210N/1250N
23
Whentheguardterminalisconnectedat“B”,theinstrumentmeasuresthe
current“I”andnotthesurfaceleakagecurrent“i1”,whichisnotincluded
inthemeasurement.SeeFigure15.Thistypeofmeasurementwillgive
thetruevalueoftheresistance“Rx”,providingthe“Ry”and“Rz”arenot
toolow.
To EARTH
terminal
I
To LINE
terminal
To Guard terminal
A
B
C
Ry
Rx
Rz
Rx: resistance through insulation
Ry: surface resistance
Rz: surface resistance
i1
Figure 15
4.2.5 Insulation Resistance Testing (MΩ Range)
After checking for a live circuit (see safety check), select the test volt-
age and connect the megohmmeter. Several connection examples are
illustrated further. Crank the handle until the green LED on the upper
right-hand side lights, ensuring that the selected test voltage has been
reached.
TEST VOLTAGE
Nopublishedstandardtellswhichvoltagetochooseforanygivenwinding.
However,publishedrecommendationscouldbesummarizedasfollows:
Rated Voltage of Motor Test Voltage
Below115 250V
115 250or500V
230 500V
460 500or1000V
24
MegohmmeterModels1210N/1250N
SPOT TESTING
Asageneralruleinspottesting,testvoltageshouldbeapplieduntilno
variationinreadingisnotedfor15secondsorappliedforaxed60sec-
onds.Oncapacitancecircuits,crankingforuptoaminuteormoremay
benecessarytofullychargethesample.Whatminimumvalueshouldbe
measured?TheIEEEstandardN°43-2000statesthatitisimpossibleto
specifythevalueofinsulationresistanceatwhichawindingwillfailelectri-
cally,butonmotors,minimumreadingsgenerallystatedare:
Rated Voltage R minimum
250 or less 2 MΩ
460 2 MΩ
Thereisnoxedgurefordeterminingwhatisgoodandbadinresistance
readings,buta goodguidewouldbe1 megohmforeveryonehundred
appliedoperatingvolts,asaminimumgure.Thisappliestomotorsand
transformers.Whentheinsulationresistancegets this low, an electrical
break-down can be expected at any time and rewinding or replacing
shouldbeconsidered.
Itisnotunusualfora winding to be 10 to100timestherecommended
minimum value (IEEE standard 43-2000: Recommended Practice for
Testing Insulation Resistance of Rotating Machinery),butthisvarieswith
temperatureandhumidity.
RATIO TESTING
Intimeresistancereading(DielectricAbsorptionRatio),readingsaretaken
at30secondsand60secondstoobtainthedielectricabsorptionratio.
Insulationresistance@60s
Insulationresistance@30s
Thistestisusefultoincreasetheaccuracyofspottesting.Ingeneral,a
ratioof1.25:2orbettershouldberequired.Aratiobelowthisindicatesthat
repairisprobablyneeded.
RememberthataDCinsulationtestmaybeusedforacceptancetesting,
butismorecommonlyusedtocheckthegradualdeteriorationofequip-
mentoveritslife.Consultyourequipmentmanufacturerforspecictestor
testvoltageifnotknown.
Insulationresistancedecreaseswithmoisture,temperatureandageand
shouldberecordedovertimeatagiventemperatureandcorrected.
=DielectricAbsorptionratio(DAR)
MegohmmeterModels1210N/1250N
25
4.2.6 Successful Insulation Resistance Testing
• Check with the equipment manufacturer for factory insulation resis-
tancereadings.
• Donotrelyoninsulationresistancetestingaloneasproofofwinding
conditions.
• Donotexpectthesamevalueforallpartsofallmachines.
• Observe consistent test time duration, recognizing that total current
throughinsulationundertestwillvarywithtime.
• Correctallreadingsproperlytoastandardreferencetemperature(see
IEEEstd#43-2000,Temperature Correction Curve).
• Knowwhatyouaretesting.Isolatethepieceofequipmentfromother
circuitry.
• Watchtrendsratherthanrelyingonsingle“spot”readings.
4.2.7 Insulation Measurement - Connections
Figures16and17showtheconnectionstomeasuretheinsulationofone
conductortotheotherconductors.Theconnectiontotheguardterminalis
usedtoeliminatetheeffectsofsurfaceleakageacrossexposedinsulation
atoneendofthecable.RefertothesectiononUtilizationoftheGuard
Terminal.Thecableshouldbedisconnectedatbothendstoavoidleakage
throughswitchboardsandpanels.
G
Cable Insulation
Conductor Under Test
Figure 16
26
MegohmmeterModels1210N/1250N
G
Cable Insulation
Conductor Under Test
Figure 17
Figure18showstheconnectionstoatransformer(lightingordistribution).
Make sure that the switches and/or circuit breakers on both sides are
open.Checkthehighvoltagewindingtoground,lowvoltagetoground,
andtheresistancebetweenthemwithnowindingground.
Tested Winding
Transformer
Grounding Lug
G
Figure 18
MegohmmeterModels1210N/1250N
27
Figure19showstheconnectionsformeasuringtheinsulationofathree-
phase line to ground by connecting the jumpers between phases. This
givesareadingofallconductorsatonce.Ifaloadsuchasamotor,heater,
etc.,isattachedtotheotherendoftheline,itwillreadtheloadresistance
togroundat thesametime.Byremoving thejumpers,readingscanbe
madebetweentheindividualconductorsandground.
~
~
~~
~
~
Jumpers
G
Figure 19
28
MegohmmeterModels1210N/1250N
4.2.8 Insulation Resistance Measurements on Motors
Figure20showsreadingtheresistancetogroundofathree-phasemotor
winding.Sincethethree-phasemotorsareinternallyconnected,itisonly
necessarytoconnectoneleadtothemotorleadandtheotherleadtothe
motorframeasshown.
G
Figure 20
Figure21showsthewindingsofathree-phasemotorseparated.Some-
timesthiscanbedoneattheleadterminalswhileothertimestheendbells
mustberemovedtogetattheleadwiresofthecoils.Byconnectingthe
megohmmeterasshown,thephaseinsulationresistancevaluecannow
bedetermined.Readbetweenphases“A”and“B”,then“B”and“C”,then
“C”and“A”.
A
B
C
G
Figure 21
MegohmmeterModels1210N/1250N
29
Figure22showsconnectionsfortestinginsulationfromasupplyconduc-
torinaswitchboxtoground(motorframe).Anidenticaltestmaybecarried
outfromthemotorstarter.
Motor Side of Switch:
Connection to One Leg
Grounded
Motor Frame
Starter In
G
Figure 22
30
MegohmmeterModels1210N/1250N
CHAPTER 5
MAINTENANCE
5.1 Warning
• Formaintenanceuseonlyoriginalfactoryreplacementparts.
• To avoid electrical shock, do not attempt to perform any servicing
unlessyouarequaliedtodoso.
• Do not perform any service while the Megohmmeter Model 1210N/
1250Nisonanycircuit.
• Toavoidelectricalshockand/ordamagetotheinstrument,donotlet
waterorotherforeignagentsintotheelectronicmodule.
Warning: IfthecrankspeedLEDisnotONduring
testing,thereadingisnotvalid.
5.2 Cleaning
The megohmmeter may be gently cleaned with a soft cloth, soap and
water. Dry immediately after cleaning.Avoid water penetration into the
electronicmodule.
Makesurethemegohmmeterandallleadsaredrybeforefurtheruse.
MegohmmeterModels1210N/1250N
31
RepairandCalibration
Toensurethatyourinstrumentmeetsfactoryspecications,werecommend
thatitbescheduledbacktoourfactoryServiceCenteratone-yearintervals
forrecalibration,orasrequiredbyotherstandardsorinternalprocedures.
For instrument repair and calibration:
You must contact our Service Center for a Customer ServiceAuthorization
Number(CSA#).Thiswillensurethatwhenyourinstrumentarrives,itwillbe
trackedandprocessedpromptly.PleasewritetheCSA#ontheoutsideofthe
shipping container. If the instrument is returned for calibration, we need to
knowifyouwantastandardcalibration,oracalibrationtraceabletoN.I.S.T.
(Includescalibrationcerticateplusrecordedcalibrationdata).
Ship To: ChauvinArnoux®,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)742-2346or(603)749-6309
E-mail:repair@aemc.com
(Orcontactyourauthorizeddistributor)
Costsforrepair,standardcalibration,andcalibrationtraceabletoN.I.S.T.are
available.
NOTE: You must obtain a CSA# before returning any instrument.
TechnicalandSalesAssistance
Ifyouareexperiencinganytechnicalproblems,orrequireanyassistancewith
theproperoperationorapplicationofyourinstrument,pleasecall,mail,faxor
e-mailourtechnicalsupportteam:
ChauvinArnoux®,Inc.d.b.a.AEMC®Instruments
200FoxboroughBoulevard
Foxborough,MA02035USA
Phone:(800)343-1391
(508)698-2115
Fax: (508)698-2118
E-mail:techsupport@aemc.com
www.aemc.com
NOTE: Do not ship Instruments to our Foxborough, MA address.
32
MegohmmeterModels1210N/1250N
Limited Warranty
TheModels1210Nand1250Narewarrantedtotheownerforaperiodofone
yearfromthedateoforiginalpurchaseagainstdefectsinmanufacture.This
limitedwarrantyis given byAEMC® Instruments,notbythe distributor from
whomitwaspurchased.Thiswarrantyisvoidiftheunithasbeentampered
with, abused or if the defect is related to service not performed byAEMC®
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:
If a malfunction occurs within the one-year period, you may return the
instrument to us for repair, provided we have your warranty registration
information on le or a proof of purchase. AEMC® Instruments will, at its
option,repairorreplacethefaultymaterial.
REGISTER ONLINE AT:
www.aemc.com
WarrantyRepairs
What you must do to return an Instrument for Warranty Repair:
First, request a Customer ServiceAuthorization Number (CSA#) by phone
orbyfaxfromourServiceDepartment(seeaddressbelow),thenreturnthe
instrumentalongwith thesignedCSAForm.Please writetheCSA#on the
outsideoftheshippingcontainer.Returntheinstrument,postageorshipment
pre-paidto:
Ship To: ChauvinArnoux®,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)742-2346or(603)749-6309
E-mail:repair@aemc.com
Caution:Toprotectyourselfagainstin-transitloss,werecommendyouinsure
yourreturnedmaterial.
NOTE: You must obtain a CSA# before returning any instrument.
Chauvin Arnoux®, Inc. d.b.a. AEMC® Instruments
15FaradayDrive•Dover,NH03820USA•Phone:(603)749-6434•Fax:(603)742-2346
www.aemc.com
09/08
99-MAN100124v11