Designation: D 257 - 99 An American National Standard Standard Test Methods for Dc Resistance or Conductance of Insulating Materials1 This standard is issued under the fixed designation D 257; the number immediately following the designation indicates the year of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscript epsilon (e) indicates an editorial change since the last revision or reapproval. This standard has been approved for use by agencies of the Department of Defense. 1. Scope D 150 Test Methods for AC Loss Characteristics and Per- 1.1 These test methods cover direct-current procedures for mittivity Dielectric Contant of Solid Electrical Insulation? the determination of dc insulation resistance, volume resis- D 374 Test Methods for Thickness of Solid Electrical Insu- tance, volume resistivity, surface resistance, and surface resis- lation? tivity of electrical insulating materials, or the corresponding D 618 Practice for Conditioning Plastics for Testing3 conductances and conductivities. D 1169 Test Method for Specific Resistance (Resistivity) of 1.2 These test methods are not suitable for use in measuring Electrical Insulating Liquids4 the electrical resistivity/conductivity of moderately conductive D 1711 Terminology Relating to Electrical Insulation? materials.UseTestMethodD4496toevaluate suchmaterials. D 4496 Test Method for DC Resistance or Conductance of 1.3 The test methods and procedures appear in the follow- Moderately Conductive Materials5 ing sections: D 5032 Practice for Maintaining Constant Relative Humid- Test Method or Procedure Section ity by Means of Aqueous Glycerin Solutionss Calculation 13 E 104 Practice for Maintaining Constant Relative Humidity Choice of Apparatus and Test Method 7 by Means of Aqueous Solutions6 Cleaning Solid Specimens 10.1 Conditioning of Specimens 11 3. Terminology Effective Area of Guarded Electrode X2 Electrode Systems 3.1 Definitions—The following definitions are taken from Factors Affecting Insulation Resistance or Conductance Terminology D 1711 and apply to the terms used in these test Measurements Humidity Control 11.2 methods. Liquid Specimens and Cells 3.1.1 conductance, insulation, n—the ratio of the total Precision and Bias Procedure for the Measurement of Resist- volumeandsurfacecurrentbetweentwoelectrodes(onorina ance or Conductance specimen)tothedc voltage applied tothe twoelectrodes. Referenced Documents 24 3.1.1.1 Discussion—Insulation conductance is the recipro- Report cal of insulation resistance. Sampling Significance and Use 3.1.2 conductance, surface, n—the ratio of the current Specimen Mounting between two electrodes (on the surface of a specimen) to the dc Summary of Test Methods Terminology voltage applied to the electrodes. Test Specimens for Insulation, Volume, and Surface 3.1.2.1 Discussion(Some volume conductance is un- Resistance or Conductance Determination &X avoidablyincludedintheactualmeasurement.)Surfacecon- Typical Measurement Methods ductance is the reciprocal of surface resistance 1.4 This standard does not purport to address all of the 3.1.3 conductance, volume, n—the ratio of the current in the safety concerns, if any, associated with its use. It is the volumeofaspecimenbetweentwoelectrodes(onorinthe responsibility of the user of this standard to establish appro- specimen)tothedcvoltageappliedtothetwoelectrodes. priate safety and health practices and determine the applica- 3.1.3.1 Discussion—Volume conductance is the reciprocal bility of regulatory limitations prior to use. For a specific of volume resistance. hazard statement, see 6.1.8. 3.1.4 conductivity, surface, nthe surface conductance multiplied by that ratio of specimen surface dimensions (dis- 2. Referenced Documents tance between electrodes divided by the width of electrodes 2.1 ASTM Standards: defining the current path) which transforms the measured 1 These test methods are under the