PresentedataMeetingofASTMCommitteeD~9Philadelphia,Pa.,February^,1956Reg.U.S.Pat.Off.AS1MSpecialTechnicalPublicationNo.188Price$1.75,tomembers$1.35PublishedbytheAMERICANSOCIETYFORTESTINGMATERIALS1916RaceSt.,Philadelphia3,Pa.SYMPOSIUMONMINIMUMPROPERTYVALUESOFELECTRICALINSULATINGMATERIALSCopyright,1957,bytheAMERICANSOCIETYFORTESTINGMATERIALSPrintedinBaltimore,Md.November,1956FOREWORDThoughfactorofsafetyissometimesfacetiouslycalledtoas"factorofignorance,"thereissomebasisforreferringtoitassuch.Inthedesignofelectricalequipment,forexample,thesafetyfactorisbasedontheminimumexpectedvaluesforelectricalandphysicalpropertiesofthecomponentma-terials,aswellasanestimateoftheextremesofconditionswhichtheequipmentmayencounterunderadversecircumstances.Resultsofmate-rialstestsshouldenableapredictionastothelowestexpectedvalueforapropertyofamaterialsothatthedesignermaytakethisintoaccounthiestablishingthesafetyfactor.Unfortunatelythisinformationisnotreadilyobtainablefrommanypresenttestmethods.Thoughtherehasbeensomeprogressinestablishingproceduresforpredictingminimumvalues,thereisstillgreatneedforfurtherwork.Thissymposiummaybeconsideredasareportofprogress,indicatingabaselineforadditionalinvestigationstowardestablishingsafetyfactoronabasisofknowledgeratherthanigno-rance.ThisSymposiumonMinimumPropertyValuesofElectricalInsulatingMaterialswasheldinPhiladelphia,Pa.,onFebruary14,1956,asaspecialfeatureofthewintermeetingofCommitteeD-9onElectricalInsulatingMaterialsoftheAmericanSocietyforTestingMaterials.TheprogramwasarrangedbyC.L.Craig,SperryGyroscopeCo.,withtheassistanceandcooperationofSubcommitteeXIonSignificanceofTestsofwhichMr.CraigisChairman,andSubcommitteeXVonTechnicalPapersandRe-search,L.B.Schofield,Chairman.Mr.Craigpresided,assistedbyMr.C.J.Photiadis(Westinghouse).iiiNOTE—TheSocietyisnotresponsible,asabody,forthestatementsandopinionsadvancedinthispublication.CONTENTSPageSignificanceofMinimumPropertyValuesofElectricalInsulatingMaterials—C.L.Craig.1ExtremalNatureofDielectricBreakdown-Ef...
