ASTM D4872 covers the determination of dissipation factor, permittivity (dielectric constant), and AC volume resistivity of wire and cable filling compounds and related materials that are solid at room temperature but can be melted at elevated temperatures.
A measured volume of melted sample is placed into a level preheated specimen dish, cooled, and primary/secondary electrodes are placed in contact with the specimen surface. Dissipation factor and permittivity are determined at 1 MHz per ASTM D150, and volume resistivity per ASTM D257.
These dielectric properties of cable fillers are controlled to ensure the cable’s electrical performance falls within design limits. Relatively small amounts of contaminants such as polar compounds, water, or salts can degrade the cable’s electrical properties.