1. Performance indicators of insulating materials
    Performance indicators of insulating materials commonly used by electricians include insulation strength, tensile strength, specific gravity, expansion coefficient, etc.
    (1) Withstand voltage: When the electric field strength of an insulating material increases to a certain limit in an electric field, it will break down. The electric field strength at which the insulation breaks down is called the insulation withstand voltage (also known as dielectric strength or insulation strength), which is usually expressed as the voltage KV value that a 1 mm thick insulating material can withstand.
    (2) Tensile strength: The tensile force that an insulating material can withstand per unit cross-sectional area, for example, glass can withstand 140 kilograms per square centimeter of cross-sectional area.
    (3) Density: The mass of an insulating material per cubic meter of volume, for example, sulfur has 2 grams per cubic meter of volume.
    (4) Expansion coefficient: The degree to which the volume of an insulator increases after being heated.

 2. Heat resistance level of insulation materials

    (1) Y-class insulating materials: natural textiles such as wood, cotton, fiber, textiles based on cellulose acetate and polyamide, and plastics that are easy to decompose and have a low melting point. Maximum working temperature: 90 degrees.
    (2) A-class insulating materials: Y-class materials working in mineral oil and impregnated with oil or oil resin composite glue, enameled wire, varnished cloth, varnished silk insulation and oil-based paint. Asphalt paint, etc. Maximum working temperature: 105 degrees.
    (3) E-class insulating materials: polyester film and A-class material composite, glass cloth, oil-based resin paint, polyvinyl acetal high-strength enameled wire, vinyl acetate heat-resistant enameled wire. Maximum working temperature: 120 degrees.
    (4) B-class insulating materials: polyester film, mica impregnated with suitable resin, glass fiber, asbestos, etc., polyester paint, polyester enameled wire. Maximum working temperature: 130 degrees.
    (5) Class F insulation materials: mica products reinforced with organic fiber materials, glass fiber and asbestos, glass wool cloth, laminated products based on glass fiber cloth and asbestos fiber, mica powder products reinforced with inorganic materials and stone tape, polyester or alkyd materials with good chemical and thermal stability, composite silicone organic polyester paint. Maximum working temperature: 155 degrees.
    (6) Class H insulation materials: mica products without reinforcement or reinforced with inorganic materials, thickened Class F materials, composite mica, organic silicon mica products, silicone organic paint, silicone organic rubber, polyimide composite glass cloth, composite film, polyimide paint, etc. Maximum working temperature: 180 degrees.
    (7) Class C insulation materials: inorganic materials that do not use any organic adhesive and grade impregnation, such as quartz, asbestos, mica, glass and electric porcelain materials, etc. Maximum working temperature: above 180 degrees.

3. Classification of insulation materials

    The insulating materials commonly used by electricians can be divided into inorganic materials, organic insulating materials and mixed insulating materials according to their chemical properties.

    (1) Inorganic insulating materials: mica, asbestos, marble, porcelain, glass, sulfur, etc., mainly used for motor and electrical winding insulation, switch base and insulators, etc.
    (2) Organic insulating materials: shellac, resin, rubber, cotton yarn, paper, hemp, silk, rayon, mostly used to make insulating varnish, winding wire coating insulation, etc.
    (3) Mixed insulating materials: various shaped insulating materials made from the above two materials, used as electrical bases, shells, etc.