ASTM-D257-99

Designation:D257–99AnAmericanNationalStandardStandardTestMethodsforDCResistanceorConductanceofInsulatingMaterials1ThisstandardisissuedunderthefixeddesignationD257;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginaladoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscriptepsilon(e)indicatesaneditorialchangesincethelastrevisionorreapproval.ThisstandardhasbeenapprovedforusebyagenciesoftheDepartmentofDefense.1.Scope1.1Thesetestmethodscoverdirect-currentproceduresforthedeterminationofdcinsulationresistance,volumeresis-tance,volumeresistivity,surfaceresistance,andsurfaceresis-tivityofelectricalinsulatingmaterials,orthecorrespondingconductancesandconductivities.1.2Thesetestmethodsarenotsuitableforuseinmeasuringtheelectricalresistivity/conductivityofmoderatelyconductivematerials.UseTestMethodD4496toevaluatesuchmaterials.1.3Thetestmethodsandproceduresappearinthefollow-ingsections:TestMethodorProcedureSectionCalculation13ChoiceofApparatusandTestMethod7CleaningSolidSpecimens10.1ConditioningofSpecimens11EffectiveAreaofGuardedElectrodeX2ElectrodeSystems6FactorsAffectingInsulationResistanceorConductanceMeasurementsX1HumidityControl11.2LiquidSpecimensandCells9.4PrecisionandBias15ProcedurefortheMeasurementofResist-anceorConductance12ReferencedDocuments2Report14Sampling8SignificanceandUse5SpecimenMounting10SummaryofTestMethods4Terminology3TestSpecimensforInsulation,Volume,andSurfaceResistanceorConductanceDetermination9TypicalMeasurementMethodsX31.4Thisstandarddoesnotpurporttoaddressallofthesafetyconcerns,ifany,associatedwithitsuse.Itistheresponsibilityoftheuserofthisstandardtoestablishappro-priatesafetyandhealthpracticesanddeterminetheapplica-bilityofregulatorylimitationspriortouse.Foraspecifichazardstatement,see6.1.8.2.ReferencedDocuments2.1ASTMStandards:D150TestMethodsforACLossCharacteristicsandPer-mittivityDielectricContantofSolidElectricalInsulation2D374TestMethodsforThicknessofSolidElectricalInsu-lation2D618PracticeforConditioningPlasticsforTesting3D1169TestMethodforSpecificResistance(Resistivity)ofElectricalInsulatingLiquids4D1711TerminologyRelatingtoElectricalInsulation2D4496TestMethodforDCResistanceorConductanceofModeratelyConductiveMaterials5D5032PracticeforMaintainingConstantRelativeHumid-itybyMeansofAqueousGlycerinSolutions5E104PracticeforMaintainingConstantRelativeHumiditybyMeansofAqueousSolutions63.Terminology3.1Definitions—ThefollowingdefinitionsaretakenfromTerminologyD1711andapplytothetermsusedinthesetestmethods.3.1.1conductance,insulation,n—theratioofthetotalvolumeandsurfacecurrentbetweentwoelectrodes(onorinaspecimen)tothedcvoltageappliedtothetwoelectrodes.3.1.1.1Discussion—Insulationconductanceistherecipro-calofinsulationresistance.3.1.2conductance,surface,n—theratioofthecurrentbetweentwoelectrodes(onthesurfaceofaspecimen)tothedcvoltageappliedtotheelectrodes.3.1.2.1Discussion—(Somevolumeconductanceisun-avoidablyincludedintheactualmeasurement.)Surfacecon-ductanceisthereciprocalofsurfaceresistance.3.1.3conductance,volume,n—theratioofthecurrentinthevolumeofaspecimenbetweentwoelectrodes(onorinthespecimen)tothedcvoltageappliedtothetwoelectrodes.3.1.3.1Discussion—Volumeconductanceisthereciprocalofvolumeresistance.3.1.4conductivity,surface,n—thesurfaceconductancemultipliedbythatratioofspecimensurfacedimensions(dis-tancebetweenelectrodesdividedbythewidthofelectrodesdefiningthecurrentpath)whichtransformsthemeasured1ThesetestmethodsareunderthejurisdictionofASTMCommitteeD-9onElectricalandElectronicInsulatingMaterialsandarethedirectresponsibilityofSubcommitteeD09.12onElectricalTests.CurrenteditionapprovedOct.10,1999.PublishedNovember1999.OriginallypublishedasD257–25T.LastpreviouseditionD257–93(1998).2AnnualBookofASTMStandards,Vol10.01.3AnnualBookofASTMStandards,Vol08.01.4AnnualBookofASTMStandards,Vol10.03.5AnnualBookofASTMStandards,Vol10.02.6AnnualBookofASTMStandards,Vol11.03.1Copyright©ASTM,100BarrHarborDrive,WestConshohocken,PA19428-2959,UnitedStates.conductancetothatobtainediftheelectrodeshadformedtheoppositesidesofasquare.3.1.4.1Discussion—Surfaceconductivityisexpressedinsiemens.Itispopularlyexpressedassiemens/square(thesizeofthesquareisimmaterial).Surfaceconductivityisthereciprocalofsurfaceresistivity.3.1.5conductivity,volume,n—thevolumeconductancemultipliedbythatratioofspecimenvolumedimensions(distancebetweenelectrodesdividedbythecross-sectionalareaoftheelectrodes)whichtransformsthemeasuredconduc-tancetothatconductanceobtainediftheelectrodeshadformedtheoppositesidesofaunitcube.3.1.5.1Discussion—Volumeconductivityisusuallyex-pressedinsiemens/centimetreorinsiemens/metreandisthereciprocalofvolumeresistivity.3.1.6moderatelyconductive,adj—describesasolidmate-rialhavingavolumeresistivitybetween1and10000000V-cm.3.1.7resistance,insulation,(Ri),n—theratioofthedcvoltageappliedtotwoelectrodes(onorinaspecimen)tothetotalvolumeandsurfacecurrentbetweenthem.3.1.7.1Discussion—Insulationresistanceisthereciprocalofinsulationconductance.3.1.8resistance,surface,(