ASTM_D_257_-_14.pdf

Designation:D25714Standard Test Methods forDC Resistance or Conductance of Insulating Materials1This standard is issued under the fixed designation D257;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the U.S.Department of Defense.1.Scope*1.1 These test methods cover direct-current procedures forthe measurement of dc insulation resistance,volume resistance,and surface resistance.From such measurements and thegeometric dimensions of specimen and electrodes,both vol-ume and surface resistivity of electrical insulating materialscan be calculated,as well as the corresponding conductancesand conductivities.1.2 These test methods are not suitable for use in measuringthe electrical resistance/conductance of moderately conductivematerials.Use Test Method D4496 to evaluate such materials.1.3 This standard describes several general alternativemethodologies for measuring resistance(or conductance).Specific materials can be tested most appropriately by usingstandardASTM test methods applicable to the specific materialthat define both voltage stress limits and finite electrificationtimes as well as specimen configuration and electrode geom-etry.These individual specific test methodologies would bebetter able to define the precision and bias for the determina-tion.1.4 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:2D150 Test Methods for AC Loss Characteristics and Permit-tivity(Dielectric Constant)of Solid Electrical InsulationD374 Test Methods for Thickness of Solid Electrical Insu-lation(Withdrawn 2013)3D1169 Test Method for Specific Resistance(Resistivity)ofElectrical Insulating LiquidsD1711 Terminology Relating to Electrical InsulationD4496 Test Method for D-C Resistance or Conductance ofModerately Conductive MaterialsD5032 Practice for Maintaining Constant Relative Humidityby Means of Aqueous Glycerin SolutionsD6054 Practice for Conditioning Electrical Insulating Mate-rials for Testing(Withdrawn 2012)3E104 Practice for Maintaining Constant Relative Humidityby Means of Aqueous Solutions3.Terminology3.1 Definitions:3.1.1 The following definitions are taken from TerminologyD1711 and apply to the terms used in the text of this standard.3.1.2 conductance,insulation,nthe ratio of the totalvolume and surface current between two electrodes(on or in aspecimen)to the dc voltage applied to the two electrodes.3.1.2.1 DiscussionInsulation conductance is the recipro-cal of insulation resistance.3.1.3 conductance,surface,nthe ratio of the currentbetween two electrodes(on the surface of a specimen)to the dcvoltage applied to the electrodes.3.1.3.1 Discussion(Some volume conductance is unavoid-ably included in the actual measurement.)Surface conductanceis the reciprocal of surface resistance.3.1.4 conductance,volume,nthe ratio of the current in thevolume of a specimen between two electrodes(on or in thespecimen)to the dc voltage applied to the two electrodes.3.1.4.1 DiscussionVolume conductance is the reciprocalof volume resistance.3.1.5 conductivity,surface,nthe surface conductancemultiplied by that ratio of specimen surface dimensions(dis-tance between electrodes divided by the width of electrodesdefining the current path)which transforms the measuredconductance to that obtained if the electrodes had formed theopposite sides of a square.1These test methods are under the jurisdiction of ASTM Committee D09 onElectrical and Electronic Insulating Materials and are the direct responsibility ofSubcommittee D09.12 on Electrical Tests.Current edition approved April 1,2014.Published May 2014.Originallyapproved in 1925.Last previous edition approved in 2007 as D257 07.DOI:10.1520/D0257-14.2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.3The last approved version of this historical standard is referenced onwww.astm.org.*A Summary of Changes section appears at the end of this standardCopyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 3.1.5.1 DiscussionSurface conductivity is expressed insiemens.It is popularly expressed as siemens/square(the sizeof the square is immaterial).Surface conductivity is thereciprocal of surface resistivity.3.1.6 conductivity,volume,nthe volume conductancemultiplied by that ratio of specimen volume dimensions(dista