megohmmeter 1250n - davis4 megohmmeter models 1210n/1250n 1.2 definition of measurement categories...

MEGOHMMETER 1210N1250N

E N G L I S H User Manual

V 500V

1kV

x 10

300

0 100200

400500

600

2015

304050

100200500

50 20 10 5 4 32

1.5

101 (1kV)

(250V)(500V)

MΩ

MEGOHMMETERModel 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® Instrumentswww.aemc.com

Table of Contents

1. INTRODUCTION ...................................................................31.1 International Electrical Symbols .....................................................31.2 DefinitionofMeasurementCategories ...........................................41.3 ReceivingYourShipment ...............................................................41.4 OrderingInformation ......................................................................4

1.4.1 AccessoriesandReplacementParts ................................4

2. PRODUCT FEATURES ..........................................................52.1 Description .....................................................................................52.2 Model1210NFeatures ..................................................................62.3 Model1250NFeatures ..................................................................62.4 Model1210NControlFeatures ......................................................72.5 Model1250NControlFeatures ......................................................82.6 1210Nand1250NControlFeatures ..............................................9

3. SPECIFICATIONS ...............................................................103.1 Model1210NSpecifications ........................................................10

3.1.1 ElectricalSpecifications ...................................................103.1.2 MechanicalSpecifications ............................................... 113.1.3 SafetySpecifications ....................................................... 11

3.2 Model1250NSpecifications ........................................................123.2.1 ElectricalSpecifications ...................................................123.2.2 MechanicalSpecifications ...............................................123.2.3 SafetySpecifications .......................................................13

4. OPERATION .......................................................................144.1 UsingtheModel1210N ...............................................................14

4.1.1 InstrumentGroundTerminal ............................................144.1.2 Auto-ranging ....................................................................144.1.3 SafetyCheck-VoltageTest ...........................................144.1.4 InsulationResistanceTesting(MΩRange) .....................144.1.5 SuccessfulInsulationResistanceTesting ........................164.1.6 InsulationMeasurement—Connections ........................164.1.7 InsulationResistanceMeasurementsonMotors ............19

2 MegohmmeterModels1210N/1250N

4.2 UsingtheModel1250N ...............................................................214.2.1 InstrumentGroundTerminal ............................................214.2.2 Auto-ranging ....................................................................214.2.3 SafetyCheck-VoltageTest ...........................................214.2.4 UtilizationoftheGuardTerminal .....................................214.2.5 InsulationResistanceTesting(MΩRange) .....................234.2.6 SuccessfulInsulationResistanceTesting ........................254.2.7 InsulationMeasurement-Connections ...........................254.2.8 InsulationResistanceMeasurementsonMotors ............28

5. MAINTENANCE ..................................................................305.1 Warning .......................................................................................305.2 Cleaning .......................................................................................30

RepairandCalibration .................................................................................31TechnicalandSalesAssistance ..................................................................31Limited Warranty .........................................................................................32WarrantyRepairs .........................................................................................32

MegohmmeterModels1210N/1250N 3

CHAPTER 1

INTRODUCTION

Warning Thesesafetywarningsareprovidedtoensurethesafetyofpersonnelandproperoperationoftheinstrument.• Readtheinstructionmanualcompletelyandfollowallsafety

informationbeforeoperatingthisinstrument.• Safetyistheresponsibilityoftheoperator!• Testsaretobecarriedoutonlyondeadcircuits!Checkforlive

circuitsbeforemakingresistancemeasurements(safetycheck).• TheMegohmmeterModels1210N/1250Naresourcesofhigh

voltage,asisthesampleconnectedtothem.Allpersonsperform-ingorassistinginthetestsmustemployallsafetyprecautionstopreventelectricalshocktothemselvesandtoothers.

• AEMC®Instrumentsconsiderstheuseofrubberglovestobeanexcellentsafetypracticeeveniftheequipmentisproperlyoperatedandcorrectlygrounded.

• Whentestingcapacitancesamples,makesurethattheyhavebeenproperlydischargedandthattheyaresafetotouch.Dielectricinsulationsamplesshouldbeshort-circuitedforatleastfivetimestheamountoftimetheywereenergized.

• Usetheleadssuppliedwiththemegohmmeter.Ifdefectiveorused,replacebeforetesting.

1.1 International Electrical SymbolsThissymbolsignifiesthattheinstrumentisprotectedbydoubleorrein-forcedinsulation.Useonlyspecifiedreplacementpartswhenservicingtheinstrument.

This symbol on the instrument indicates a WARNING and that theoperatormustrefertotheusermanualforinstructionsbeforeoperatingthe instrument. In this manual, the symbol preceding instructionsindicatesthatiftheinstructionsarenotfollowed,bodilyinjury,installation/sampleandproductdamagemayresult.

Riskofelectricshock.Thevoltageatthepartsmarkedwiththissymbolmaybedangerous.


1.2 DefinitionofMeasurementCategoriesCat. 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 ReceivingYourShipmentUponreceivingyourshipment,makesurethatthecontentsareconsistentwith thepacking list.Notify yourdistributor of anymissing items. If theequipmentappearstobedamaged,fileaclaimimmediatelywiththecar-rierandnotifyyourdistributoratonce,givingadetaileddescriptionofanydamage.Savethedamagedpackingcontainertosubstantiateyourclaim.Donotuseaninstrumentthatappearstobedamaged.

1.4 Ordering Information

Megohmmeter Model 1210N .............................................Cat. #1326.01

Megohmmeter Model 1250N .............................................Cat. #1326.02Both 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 PartsSetof10fuses,0.2A,250Vfast-blow5x20mm...................Cat. #2973.02Leadpouchwiththreecolor-codedsafetyleads,groundlead,twosafetyalligatorclipsandtestprobe..........Cat. #1019.01Leadpouchwiththreecolor-codedleads,groundlead,twoalligatorclips,andtestprobe ...................Cat. #1017.56


CHAPTER 2

PRODUCT FEATURES

2.1 DescriptionTheAEMC®Models1210Nand1250Narecompact,self-containedhand-crankedmegohmmeters.Theyarepracticalanddependableinstrumentsdesignedforabroadrangeofplantandfieldserviceapplications,suchas acceptance testing and preventive maintenance of wiring, cables,switchgear, and motors. The easy hand-cranked operation provides asteadyrectifiedDCvoltageoutputacrosstheentirerangeforconsistentlyreliablereadings.These megohmmeters incorporate a built-in, sealed alternator and aconstant DC voltage circuit to provide a stable output and give directinsulationresistancereading.Theyare ruggedlybuilt anduseanO-ring-sealed, castaluminumcasewithapolycarbonatefrontpaneldesignedforharsh,heavy-dutyuseandprotectionagainstdustandwater.The Models 1210N/1250N have a unique auto-ranging feature whichexpandsthescalebyx10andalmostdoublesthescalelength.Whenthepointerreachesneartheendofscale,theauto-rangingfeatureactivates,returningthepointertothebeginningofthescalewiththex10redLEDindicator on.Insulation resistance is indicatedwith a rugged taut-bandmetermove-mentonalogarithmicscale.Theindicatorscaleiseasytoread.


2.2 Model1210NFeatures• Measuresinsulationat500V,resistance,continuity

• Testvoltageconstantacrosstheentiremeasurementrange

• AutorangingMΩ,kΩandΩranges

• Designedforharshenvironments:offshore,mining,heavy-dutyfield,industrial,andmilitaryuse

• Extraruggedcastaluminumcase;O-ringsealedagainstrain,water,anddust;aluminumlid

• Compact,self-containedpackage;foldingcrank

• Largedirect-readingscale

• 600Vtestvoltagerange(safetycheck)

2.3 Model1250NFeatures• Threetestvoltages:250,500,1000V

• Testvoltageconstantacrosstheentiremeasurementrange

• AutorangingMΩranges

• Designedforharshenvironments:offshore,mining,heavy-dutyfield,industrial,andmilitaryuse

• Extraruggedcastaluminumcase;O-ringsealedagainstrain,water,anddust;aluminumlid

• Compact,self-containedpackage,foldingcrank

• Fourterminalsincludingguardandground

• Largedirect-readingscale

• 600Vtestvoltagerange(safetycheck)


2.4 Model1210NControlFeatures

kΩΩ

MV

x 10

5

01

26 7

10

V

FUS

123

451020

1020 30

0.5

50

(500V)(1mA)

(5mA)

ΜΩ

2 ! C42

300

0

100200 400 500

600Ω

κΩ 43 89

40

0

Ω

MEGOHMMETER

Model 1210NINSTRUMENTS

®

600V CAT II / 1000V CAT I !

1 2 3

4

5

6

7

8

9

10

Figure 1

1. Line(-)terminalBlack

2. Fuse0.2A

3. Earth(+)terminalRed

4. Instrumentgroundterminalforusersafety

5. AmberLEDilluminateswhenpropercrankspeedisattained,indicatingpresenceofselectedoutput

6. Foldawayhandle

7. Mechanicalzeroadjustmentscrew

8. Rangeswitch-safetytestfirstonMΩ/Vrangeto500VAC

9. Autoranging:RedLEDilluminateswhenreadingneedstobemultipliedx10toobtainthetruevalue(MΩ,kΩ,Ωranges)

10.Securityfingerrestisolatesusershandfromterminalswhilegivingafirmgripduringanoperation


2.5 Model1250NControlFeatures

V500V

1kV25

0V

x 10

300

0

100200 400 500

600

V

G

20 153040

50100200500

5020 10

5 4 3 2 1.510

1

(1kV)(250V)

(500V)

ΜΩ

2 ! C42

MEGOHMMETER

Model 1250NINSTRUMENTS

®

600V CAT II / 1000V CAT I !

1 2 3

4

5

6

7

8

9

10

Figure 1-A

1. Line(-)terminal-Black

2. Guardterminal-Blue

3. Earth(+)terminal-Red

4. Instrumentgroundterminalforusersafety

5. GreenLEDilluminateswhenpropercrankspeedisattained,indicatingpresenceofselectedtestvoltage

6. Foldawayhandle

7. Mechanicalzeroadjustmentscrew

8. Rangeswitch-Safetytestfirston500V/V~rangeto500VAC

9. Autoranging:RedLEDilluminateswhenreadingneedstobemultipliedx10toobtainthetruevalue(MΩrange)

10.Securityfingerrestisolatesusershandfromterminalswhilegivingafirmgripduringanoperation


2.6 1210Nand1250NControlFeatures

11.Long,sturdyassemblyboltsfortightcaseclosing.

12. Instrumentgroundterminalforenhancedusersafety.

13. Ruggedtaut-bandmeter movement.

14.Switchslideassembly.

15.Alternatorcrankshaft,gearsandbearingspermanentlylubricatedand sealed.

16.Foldawaycrank.

17.Diecastaluminumcase(covernotshown).

18.O-ringconstructionsealsoutdirtandwater.

19.Simpleprintedcircuitboardassemblyforeasy calibration and maintenance.

20.Highimpactpolycar-bonatefaceplate. Figure 2

12

13

14

15

16

17

18

19

20

11


CHAPTER 3

SPECIFICATIONS

3.1 Model1210NSpecifications

3.1.1 ElectricalSpecifications

INSULATION TESTSDC Test Voltage: 500V(testvoltagegeneratedinfullacrosstheentiremeasurementrange)Megohm Range (Auto-ranging): 0.5 to 5.5MΩ;5.5to200MΩShort Circuit Current: 5mA(max)Accuracy:2.5%offullscalelengthCharging Time: 0.5s/µFDischarging Time (Auto): 5s/µF

RESISTANCE TESTSDC Test Current:1mAconstant,600VmaxKilohm Range (Auto-ranging): 0to45kΩ;45to500kΩAccuracy: 2.5%fullscalelengthCharging Time: 0.5s/µFDischarging Time (Auto): 5s/µF

CONTINUITY TESTSDC Test Current: 5mAconstant,10VmaxOhm Range (Auto-ranging): 0 to 9Ω;9to100Ω Accuracy: 2%offullscalelengthFuse Protection: 0.2A,250V,fast-blow,5x20mm

VOLTAGE TESTS (Safety Check):Voltage Range: 0to600VACFrequency: 45 to 450HzAccuracy: 3%offullscaleInput Impedance: 100kΩ(approx)


3.1.2 MechanicalSpecificationsTest Voltage Indicator:AmberLEDindicatespropertestvoltageandcrankspeed

Scale: Directreadingsonallranges;3"(76mm),blackonwhite

Autorange Indicator:RedLEDindicatesAuto-range;multiplyresistancereadingsx10

Power Supply:Hand-cranked,heavydutybrushlessalternatorandsolidstaterectifica-tionandamplificationforstablevoltage;testvoltagereachedat140rpm(approx)

Dielectric Test: 2000V50/60Hz,between(-),(+),andgroundterminals

Meter Movement: Ruggedtautbandsuspension

Dimensions: 4.7x4.7x5.1"(120x120x130mm)

Weight: 3.3lbs(1.5kg)

Temperature Range:Reference range:64to75°F(18to24°C),30-50%RHOperating range:14to122°F(-10to50°C),0-80%RHStorage range:-4to176°F(-20to80°C),0-90%RH

Case:Castaluminumalloycaseandlidpaintedsafetyyellow,withheavydutygraypolycarbonatefrontpanel;O-ringsealbetweenfrontpanelandcase;sealedagainstwateranddust;foldingcrank

Terminals:“+”Line(red);“-”earth(black);acceptsstandard4mmsafetybananaplugs;groundaccepts4mmbananaplugorspadelugs

3.1.3 SafetySpecificationsSealed: IP54withlid,IP52withoutlid

Insulation Tester:VDE413part1/4exceptf

Safety:IEC1010-1;600VCATII;1000VCATI

Envelope Protection: IEC529

Vibration: MIL-T-38800D

Shock: IEC51


3.2 Model1250NSpecifications

3.2.1 ElectricalSpecifications

INSULATION TESTS

DC Test Voltages: 250,500,1000V(Testvoltagesgeneratedinfullacrosstheentiremeasurementrange)

Megohm Ranges (Auto-ranging):250V: 1to11MΩ 11 to 500MΩ

500V: 1to11MΩ 11 to 500MΩ

1000V: 10to110MΩ 110 to 5000MΩ

Short Circuit Current:5mA(approx)

Accuracy:2%offullscalelength

Charging Time: 250V:0.2s/µF 500V:0.5s/µF 1000V:0.5s/µF

Discharging Time (Auto): 8s/µF

VOLTAGE TESTS (Safety Check)

Voltage Range:0to600VAC

Accuracy:3%offullscale

3.2.2 MechanicalSpecificationsTest Voltage Indicator:GreenLEDindicatespropertestvoltageandcrankspeed

Warning: IfthecrankspeedLEDisnotONduringtest-ing,thereadingisnotvalid.

Scale:Directreadingsonallranges;3"(76mm),blackonwhite


Autorange Indicator:RedLEDindicatesautorange;multiplyresistancereadingsx10

Dielectric Test: 2000V50/60Hz,between(-),(+),guardandgroundterminals

Power Supply:Hand-cranked,heavydutybrushlessalternatorandsolidstate rectifica-tionandamplificationforstablevoltage;testvoltagereachedat140rpm(approx)

Meter Movement:Ruggedtautbandsuspension

Dimensions: 4.7x4.7x5.1"(120x120x130mm)

Weight: 3.3lbs(1.5kg)

Temperature Range:Reference range: 64to75°F(18to24°C),30-50%RHOperating range: 14to122°F(-10to50°C),0-80%RHStorage range: -4to176°F(-20to80°C),0-90%RH

Case:Castaluminumalloycaseandlidpaintedsafetyyellow,withheavydutygraypolycarbonatefrontpanel;O-ringsealbetweenfrontpanelandcase;sealedagainstwateranddust;foldingcrank

Terminals:“+”Line(red);“-”earth(black);“G”guard(blue);acceptssafety4mmbananaplugs;groundaccepts4mmbananaplugsorspadelug

3.2.3 SafetySpecificationsSealed:IP54withlid,IP52withoutlid

Insulation Tester: VDE413part1/4exceptf

Safety: IEC1010-1;600VCATII;1000VCATI

Envelope Protection:IEC529

Vibration: MIL-T-38800D

Shock: IEC51

*All specifications are subject to change without notice


CHAPTER 4

OPERATION

4.1 UsingtheModel1210N

4.1.1 Instrument Ground TerminalTheMegohmmeterModel1210Nisequippedwithaninstrumentgroundterminalforenhancedusersafety.Groundyourinstrumentwheninuse.

4.1.2 Auto-rangingHow it works:Whenthepointerreachesapproximately90%of thefullscale length, theauto-range is triggered, the redauto-range (x10)LEDlightsup.Thepointergoesbacktothebeginningofthescaleandresumesitstravel.Thereadingsshouldbemultipliedby10whenthex10LEDison.

4.1.3 Safety Check - Voltage Test Beforemeasuring insulation resistance, confirm that thesample is fullydischarged (particularly indielectricandcapacitancesamples)and thatthesampleisnotconnectedtoanenergizedcircuit.

Toperformthevoltagetest,settherangeselectiontoV(MΩ),connectandreadontheredvoltagescale(600VACmax).DO NOT CRANK.Ifmeasur-ingonaDCcircuit,thepointerwilldeflectbutthemeasurementmaybeinaccurate.

4.1.4 Insulation Resistance Testing (MΩ Range)Aftercheckingforalivecircuit(seeSafetyCheckabove),selecttheMΩ rangeandconnectthemegohmmeter.Severalconnectionexamplesareillustrated further. Crank the handle until the amber LED on the upperright-handsidelights,ensuringappropriatetestvoltageattheoutput.


SPOT TESTINGAsageneralruleinspottesting,testvoltageshouldbeapplieduntilnovariationinreadingisnotedfor15secondsorappliedforafixed60sec-onds.Oncapacitancecircuits,crankingforuptoaminuteormoremaybenecessarytofullychargethesample.Whatminimumvalueshouldbemeasured?TheIEEEstandardN°43-2000statesthatitisimpossibletospecifythevalueofinsulationresistanceatwhichawindingwillfailelectri-cally,butonmotors,minimumreadingsgenerallystatedare:

Rated Voltage R minimum250 or less 2 MΩ

460 2 MΩ

Thereisnofixedfigurefordeterminingwhatisgoodandbadinresistancereadings,butagoodguidewouldbe1megohmforeveryonehundredappliedoperatingvolts,asaminimumfigure.Thisappliestomotorsandtransformers.When the insulation resistancegets this low,anelectricalbreak-down can be expected at any time and rewinding or replacingshouldbeconsidered.

It isnotunusual forawinding tobe10 to100 times therecommendedminimum value (IEEE standard 43-2000: Recommended Practice for Testing Insulation Resistance of Rotating Machinery),butthisvarieswithtemperatureandhumidity.

RATIO TESTINGIntimeresistancereading(DielectricAbsorptionRatio),readingsaretakenat30secondsand60secondstoobtainthedielectricabsorptionratio.

Insulationresistance@60s


Thistestisusefultoincreasetheaccuracyofspottesting.Ingeneral,aratioof1.25:2orbettershouldberequired.Aratiobelowthisindicatesthatrepairisprobablyneeded.

RememberthataDCinsulationtestmaybeusedforacceptancetesting,butismorecommonlyusedtocheckthegradualdeteriorationofequip-mentoveritslife.Consultyourequipmentmanufacturerforspecifictestortestvoltageifnotknown.

Insulationresistancedecreaseswithmoisture,temperatureandageandshouldberecordedovertimeatagiventemperatureandcorrected.

=DielectricAbsorptionratio(DAR)


4.1.5 Successful Insulation Resistance Testing• Checkwith the equipmentmanufacturer for factory insulation resis-

tancereadings.

• Donotrelyoninsulationresistancetestingaloneasproofofwindingconditions.

• Donotexpectthesamevalueforallpartsofallmachines.

• Observe consistent test time duration, recognizing that total currentthroughinsulationundertestwillvarywithtime.

• Correctallreadingsproperlytoastandardreferencetemperature(seeIEEEstd#43-2000,Temperature Correction Curve).

• Knowwhatyouaretesting.Isolatethepieceofequipmentfromothercircuitry.

• Watchtrendsratherthanrelyingonsingle“spot”readings.

4.1.6 Insulation Measurement — ConnectionsFigure3showstheconnectionstomeasuretheinsulationofoneconduc-tor to the other conductors.The cable should be disconnected at bothendstoavoidleakagethroughswitchboardsandpanels.

Cable Insulation

Conductor Under Test

Fus

Figure 3


Figures4and5showtheconnectionsfortestinginsulationfromasupplyconductortoground(motorframe).

Cable Insulation


Fus

Figure 4

Fus

Cable Insulation


Figure 5

Figure6showstheconnectionstoatransformer(lightingordistribution).Make sure that the switches and/or circuit breakers on both sides areopen.Checkthehighvoltagewindingtoground,lowvoltagetoground,andtheresistancebetweenthemwithnowindingground.


Tested Winding

TransformerGrounding Lug

Fus

Figure 6

Figure7showstheconnectionsformeasuringtheinsulationofathree-phase line to groundby connecting the jumpersbetweenphases.Thisgivesareadingofallconductorsatonce.Ifaloadsuchasamotor,heater,etc.,isattachedtotheotherendoftheline,itwillreadtheloadresistancetogroundat thesametime.Byremoving the jumpers, readingscanbemadebetweentheindividualconductorsandground.

~~

~ ~~~

Jumpers

Fus

Figure 7


4.1.7 Insulation Resistance Measurements on MotorsFigure8showsreadingtheresistancetogroundofathree-phasemotorwinding.Sincethethree-phasemotorsareinternallyconnected,itisonlynecessarytoconnectoneleadtothemotorleadandtheotherleadtothemotorframeasshown.

Fus

Figure 8

Figure9shows thewindingsofa three-phasemotorseparated.Some-times thiscanbedoneat the lead terminals,whileother times theendbellsmustberemovedtogetattheleadwiresofthecoils.Byconnectingthemegohmmeterasshown, thephase insulationresistancevaluecannowbedetermined.Readbetweenphases“A”and“B”,then“B”and“C”,then“C”and“A”.

A

B

C

Fus

Figure 9


Figure10showsconnectionsfortestinginsulationfromasupplyconduc-torinaswitchboxtoground(motorframe).Anidenticaltestmaybecarriedoutfromthemotorstarter.

Motor Side of Switch:Connection to One Leg

GroundedMotor Frame

Starter In

Fus

Figure 10


4.2 UsingtheModel1250N

4.2.1 Instrument Ground TerminalTheMegohmmeterModel1250Nisequippedwithaninstrumentgroundterminalforenhancedusersafety.Groundyourinstrumentwheninuse.

4.2.2 Auto-rangingHow it works:When the pointer reaches approximately 90%of the fullscale length, the auto-range is triggered, the red auto-range (x10) LEDlightsup.Thepointergoesbacktothebeginningofthescaleandresumesitstravel.Thereadingsshouldbemultipliedby10whenthex10LEDison.

4.2.3 Safety Check - Voltage Test Beforemeasuring insulation resistance, confirm that thesample is fullydischarged (particularly indielectricandcapacitancesamples)and thatthesampleisnotconnectedtoanenergizedcircuit.

Toperformthevoltagetest,settherangeselectionto500V,connectandreadontheredvoltagescale(600VACmax).DO NOT CRANK.Ifmeasur-ingonaDCcircuit,thepointerwilldeflectbutthemeasurementmaybeinaccurate.

4.2.4 Utilization of the Guard Terminal

G

A

E

BC

E = Exposed surface

A = Insulation

B = Shield

C = Conductor

Figure 13


Guardterminalsareusefulwhenmeasuringhighresistancevaluesandforstabilizingreadings.

When testing the insulation at the end of a cable, it is necessary toeliminatetheerrorfromsurfaceleakagewhichoccurs,particularlyathighresistancevalues.Thepurposeoftheguardterminalistoprovideathirdterminalwithinthepathofthesurfaceleakage“E”.ConnecttheinstrumentasshowninFigure13.

Ifthereisnoshieldat“B”,useacopperwirewoundseveraltimesaroundtheexposedsurface“B”.(Note:Ifashieldisnotavailableandyoudonotmakeupashieldaround“B”andconnect to theguard terminal (-), themeasurementwillbeerroneousand lead toconfusionas to thecable’sstate.)

Iftheguardterminalisnotconnectedat“B”,theinstrumentmeasuresthecurrent “I” flowing through the insulationanda surface leakagecurrent“i1”.SeeFigure14.

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

i 1

Figure 14


Whentheguardterminalisconnectedat“B”,theinstrumentmeasuresthecurrent“I”andnotthesurfaceleakagecurrent“i1”,whichisnotincludedinthemeasurement.SeeFigure15.Thistypeofmeasurementwillgivethetruevalueoftheresistance“Rx”,providingthe“Ry”and“Rz”arenottoolow.

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

i 1

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 themegohmmeter. Several connection examples areillustrated further. Crank the handle until the green LED on the upperright-hand side lights, ensuring that the selected test voltagehasbeenreached.

TEST VOLTAGENopublishedstandardtellswhichvoltagetochooseforanygivenwinding.However,publishedrecommendationscouldbesummarizedasfollows:

Rated Voltage of Motor Test VoltageBelow115 250V

115 250or500V230 500V460 500or1000V


SPOT TESTINGAsageneralruleinspottesting,testvoltageshouldbeapplieduntilnovariationinreadingisnotedfor15secondsorappliedforafixed60sec-onds.Oncapacitancecircuits,crankingforuptoaminuteormoremaybenecessarytofullychargethesample.Whatminimumvalueshouldbemeasured?TheIEEEstandardN°43-2000statesthatitisimpossibletospecifythevalueofinsulationresistanceatwhichawindingwillfailelectri-cally,butonmotors,minimumreadingsgenerallystatedare:

Rated Voltage R minimum250 or less 2 MΩ

460 2 MΩ

Thereisnofixedfigurefordeterminingwhatisgoodandbadinresistancereadings,butagoodguidewouldbe1megohmforeveryonehundredappliedoperatingvolts,asaminimumfigure.Thisappliestomotorsandtransformers.When the insulation resistancegets this low,anelectricalbreak-down can be expected at any time and rewinding or replacingshouldbeconsidered.

It isnotunusual forawinding tobe10 to100 times therecommendedminimum value (IEEE standard 43-2000: Recommended Practice for Testing Insulation Resistance of Rotating Machinery),butthisvarieswithtemperatureandhumidity.

RATIO TESTINGIntimeresistancereading(DielectricAbsorptionRatio),readingsaretakenat30secondsand60secondstoobtainthedielectricabsorptionratio.



Thistestisusefultoincreasetheaccuracyofspottesting.Ingeneral,aratioof1.25:2orbettershouldberequired.Aratiobelowthisindicatesthatrepairisprobablyneeded.

RememberthataDCinsulationtestmaybeusedforacceptancetesting,butismorecommonlyusedtocheckthegradualdeteriorationofequip-mentoveritslife.Consultyourequipmentmanufacturerforspecifictestortestvoltageifnotknown.

Insulationresistancedecreaseswithmoisture,temperatureandageandshouldberecordedovertimeatagiventemperatureandcorrected.

=DielectricAbsorptionratio(DAR)


4.2.6 Successful Insulation Resistance Testing• Checkwith the equipmentmanufacturer for factory insulation resis-

tancereadings.

• Donotrelyoninsulationresistancetestingaloneasproofofwindingconditions.

• Donotexpectthesamevalueforallpartsofallmachines.

• Observe consistent test time duration, recognizing that total currentthroughinsulationundertestwillvarywithtime.

• Correctallreadingsproperlytoastandardreferencetemperature(seeIEEEstd#43-2000,Temperature Correction Curve).

• Knowwhatyouaretesting.Isolatethepieceofequipmentfromothercircuitry.

• Watchtrendsratherthanrelyingonsingle“spot”readings.

4.2.7 Insulation Measurement - ConnectionsFigures16and17showtheconnectionstomeasuretheinsulationofoneconductortotheotherconductors.Theconnectiontotheguardterminalisusedtoeliminatetheeffectsofsurfaceleakageacrossexposedinsulationatoneendofthecable.RefertothesectiononUtilizationoftheGuardTerminal.Thecableshouldbedisconnectedatbothendstoavoidleakagethroughswitchboardsandpanels.

G

Cable Insulation


Figure 16


G

Cable Insulation


Figure 17

Figure18showstheconnectionstoatransformer(lightingordistribution).Make sure that the switches and/or circuit breakers on both sides areopen.Checkthehighvoltagewindingtoground,lowvoltagetoground,andtheresistancebetweenthemwithnowindingground.

Tested Winding

TransformerGrounding Lug

G

Figure 18


Figure19showstheconnectionsformeasuringtheinsulationofathree-phase line to groundby connecting the jumpersbetweenphases.Thisgivesareadingofallconductorsatonce.Ifaloadsuchasamotor,heater,etc.,isattachedtotheotherendoftheline,itwillreadtheloadresistancetogroundat thesametime.Byremoving the jumpers, readingscanbemadebetweentheindividualconductorsandground.

~~

~ ~~~

Jumpers

G

Figure 19


4.2.8 Insulation Resistance Measurements on MotorsFigure20showsreadingtheresistancetogroundofathree-phasemotorwinding.Sincethethree-phasemotorsareinternallyconnected,itisonlynecessarytoconnectoneleadtothemotorleadandtheotherleadtothemotorframeasshown.

G

Figure 20

Figure21showsthewindingsofathree-phasemotorseparated.Some-timesthiscanbedoneattheleadterminalswhileothertimestheendbellsmustberemovedtogetattheleadwiresofthecoils.Byconnectingthemegohmmeterasshown,thephaseinsulationresistancevaluecannowbedetermined.Readbetweenphases“A”and“B”,then“B”and“C”,then“C”and“A”.

A

B

C

G

Figure 21


Figure22showsconnectionsfortestinginsulationfromasupplyconduc-torinaswitchboxtoground(motorframe).Anidenticaltestmaybecarriedoutfromthemotorstarter.

Motor Side of Switch:Connection to One Leg

GroundedMotor Frame

Starter In

G

Figure 22


CHAPTER 5

MAINTENANCE

5.1 Warning • Formaintenanceuseonlyoriginalfactoryreplacementparts.

• To avoid electrical shock, do not attempt to perform any servicingunlessyouarequalifiedtodoso.

• Do not perform any servicewhile theMegohmmeterModel 1210N/1250Nisonanycircuit.

• Toavoidelectricalshockand/ordamagetotheinstrument,donotletwaterorotherforeignagentsintotheelectronicmodule.

Warning: IfthecrankspeedLEDisnotONduringtesting,thereadingisnotvalid.

5.2 CleaningThemegohmmetermay be gently cleanedwith a soft cloth, soap andwater. Dry immediately after cleaning.Avoidwater penetration into theelectronicmodule.

Makesurethemegohmmeterandallleadsaredrybeforefurtheruse.


RepairandCalibration

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.

TechnicalandSalesAssistance

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

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

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


Limited Warranty

TheModels1210Nand1250Narewarrantedtotheownerforaperiodofoneyearfromthedateoforiginalpurchaseagainstdefectsinmanufacture.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:If a malfunction occurs within the one-year period, you may return theinstrument to us for repair, provided we have your warranty registrationinformation on file or a proof of purchase. AEMC® Instruments will, at itsoption,repairorreplacethefaultymaterial.

REGISTER ONLINE AT:www.aemc.com

WarrantyRepairs

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.

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

www.aemc.com

09/08

99-MAN100124v11

megohmmeter 1250n - davis4 megohmmeter models 1210n/1250n 1.2 definition of measurement categories...

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