ASTM D257-14 pdf free download.Standard Test Methods for DC Resistance or Conductance of Insulating Materials.
ASTM D257-14 covers direct-current procedures for the measurement of dc insulation resistance, volume resistance, and surface resistance. From such measurements and the geometric dimensions of specimen and electrodes, both volume and surface resistivity of electrical insulating materials can be calculated, as well as the corresponding conductances and conductivities.
These test methods are not suitable for use in measuring the electrical resistance/conductance of moderately conductive materials. Use Test Method D4496 to evaluate such materials.
4. Summary of Test Methods
4.1 The resistance or conductance of a material specimen or of a capacitor is determined from a measurement of current or of voltage drop under specilied conditions. By using the appropriate electrode systems. surface and volume resistance or conductance are measured separately.
6. Electrode Systems
6. 1 The electrodes for insulating materials are to allow intimate contact with the specimen surface, without introducing significant error because of electrode resistance or contamination of the specimen (5). The electrode material is to be corrosion-resistant tinder the conditions of the test. For tests of fabricated specimens such as feed-through bushings. cables. etc.. the electrodes employed are a part of the specimen or its mounting. In such cases, measurements of insulation resistance or conductance include the contaminating effects of electrode or mounting materials and are generally related to the performance of the specimen in actual use.
6. 1 . I Binding-Post and Taper-Pin Electrodes, Fig. I and Fig. 2. provide a means of applying voltage to rigid insulating materials to permit an evaluation of their resistive or conductive properties.