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Significance and Use
4.1 Insulating materials are used to isolate components of an electrical system from each other and from ground, as well as to provide mechanical support for the components. For this purpose, it is generally desirable to have the insulation resistance as high as possible, consistent with acceptable mechanical, chemical, and heat-resisting properties. Since insulation resistance or conductance combines both volume and surface resistance or conductance, its measured value is most useful when the test specimen and electrodes have the same form as is required in actual use. Surface resistance or conductance changes rapidly with humidity, while volume resistance or conductance changes slowly although the final change may eventually be greater.
4.2 Resistivity or conductivity is used to predict, indirectly, the low-frequency dielectric breakdown and dissipation factor properties of some materials. Resistivity or conductivity is often used as an indirect measure of moisture content, degree of cure, mechanical continuity, and deterioration of various types. The usefulness of these indirect measurements is dependent on the degree of correlation established by supporting theoretical or experimental investigations. A decrease of surface resistance will result either in an increase of the dielectric breakdown voltage because the electric field intensity is reduced, or a decrease of the dielectric breakdown voltage because the area under stress is increased.
4.3 All the dielectric resistances or conductances depend on the length of time of electrification and on the value of applied voltage (in addition to the usual environmental variables). These must be known to make the measured value of resistance or conductance meaningful.
4.4 Volume resistivity or conductivity is used as an aid in designing an insulator for a specific application. The change of resistivity or conductivity with temperature and humidity may be great, and must be known when designing for operating conditions. Volume resistivity or conductivity determinations are often used in checking the uniformity of an insulating material, either with regard to processing or to detect conductive impurities that affect the quality of the material and that may not be readily detectable by other methods.
4.5 Volume resistivities above 1021 Ω·cm (1019 Ω·m), obtained on specimens under usual laboratory conditions, are of doubtful validity, considering the limitations of commonly used measuring equipment.
4.6 Surface resistance or conductance cannot be measured accurately, only approximated, because some degree of volume resistance or conductance is always involved in the measurement. The measured value is also affected by the surface contamination. Surface contamination, and its rate of accumulation, is affected by many factors including electrostatic charging and interfacial tension. These, in turn, may affect the surface resistivity. Surface resistivity or conductivity can be considered to be related to material properties when contamination is involved but is not a material property in the usual sense.
1.1 These test methods cover procedures for testing adhesives in liquid, highly viscous, solid, or set states, that are intended to be cured by electronic heating, or that are intended to provide electrical insulation, or that are intended for use in electrical apparatus.
Power Factor and Dielectric Constant of Liquid Adhesives
Acidity and Alkalinity
(2) Procedures for Testing Properties of Adhesives As Used:
Power Factor and Dielectric Constant of a Dried or Cured Adhesive Film
Volume and Surface Resistivity
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. For a specific hazard statement, see 8.2.
2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.
D115 Test Methods for Testing Solvent Containing Varnishes Used for Electrical Insulation
D150 Test Methods for AC Loss Characteristics and Permittivity (Dielectric Constant) of Solid Electrical Insulation
D202 Test Methods for Sampling and Testing Untreated Paper Used for Electrical Insulation
D257 Test Methods for DC Resistance or Conductance of Insulating Materials
D495 Test Method for High-Voltage, Low-Current, Dry Arc Resistance of Solid Electrical Insulation
D897 Test Method for Tensile Properties of Adhesive Bonds
D907 Terminology of Adhesives
ICS Number Code 83.180 (Adhesives)
UNSPSC Code 31201601(Chemical adhesives); 30140000(Insulation)
ASTM D1304-99(2012), Standard Test Methods for Adhesives Relative to Their Use as Electrical Insulation, ASTM International, West Conshohocken, PA, 2012, www.astm.orgBack to Top