Which material is NOT listed as a common overhead line insulator material?

• A. Fiberglass
• B. Glass
• C. Glass-lined wood
• D. Nylon-reinforced plastic

Answer: (D)

Overhead line insulators are chosen for high dielectric strength, durability in weather, and light weight. Glass has been used for a long time because it provides strong electrical insulation and can withstand outdoor conditions. Fiberglass, a fiber-reinforced polymer, is popular today for insulators due to its lighter weight and excellent performance in wet conditions, which helps reduce leakage currents. Glass-lined wood represents an older design idea where a glass coating improves moisture resistance on a wooden core, combining traditional strength with better insulation. Nylon-reinforced plastic isn’t a standard material used for overhead line insulators, so it isn’t listed among the common choices. The other materials shown—glass, fiberglass, and glass-lined wood—are all known insulator materials, whereas nylon-reinforced plastic is not.