ASTM International Standard Specification for Mineral Insulating Liquid Used in Electrical Apparatus ASTM D3487-25

This specification covers two types of new mineral insulating oils of petroleum origin for use as an insulating and cooling medium in new and existing power and distribution electrical apparatuses, such as transformers, regulators, reactors, circuit breakers, switchgear, and attendant equipment. It is the intension of this specification to define a mineral insulating oil that is functionally interchangeable and miscible with existing oils, is compatible with existing apparatus and with appropriate field maintenance, and will satisfactorily maintain its functional characteristics in its application in electrical equipment. Type I mineral oils are used for apparatuses where normal oxidation resistance is required, where as, Type II mineral oils are used for apparatuses where greater oxidation resistance is required. When examined with corresponding test methods, sampled specimens shall conform accordingly to physical (aniline point, color, flash point, interfacial tension, pour point, relative density or specific gravity, viscosity, and appearance), electrical (dielectric breakdown voltage, gassing tendency, and dissipation or power factor), and chemical (oxidation stability, oxidation inhibitor content, corrosive sulfur content, water content, neutralization number, and PCB content) property requirements.