A substance with very low electrical conductivity, i.e., an insulator. Such substances have electrical conductivity of less than one-millionth mho/cm. Those with a somewhat higher conductivity(10−6 to 10−3 mho/cm) are called semiconductors. Among the more common solid dielectrics are glass, rubber and similar elastomers, and wood and other cellulosics. Liquid dielectrics include hydrocarbon oils, askarel, and silicone oils.See Transformer Oil.