Overhead insulators are made from porcelain, glass, or polymer. Which material is not typically used?

• A. Polymer
• B. Porcelain
• C. Glass
• D. Steel

Answer: (D)

The material for an overhead insulator must act as a high-resistance barrier that withstands moisture and contamination while providing mechanical strength. Porcelain and glass are traditional ceramic insulators that offer strong dielectric properties and can shed water when dirty. Polymer insulators are modern composites that are lighter and often have hydrophobic surfaces, which help reduce leakage currents in wet conditions.

Steel, in contrast, is a conductor. Using metal as the insulating body would allow current to flow, defeating the purpose of insulation. Metals are used for hardware and fittings around the insulator, not as the insulating material itself. So the material not typically used for overhead insulators is steel.