Name the main external insulator types used on overhead lines.

• A. Ring insulators, hook insulators, seamless insulators, and tubular insulators.
• B. Pin insulators, suspension insulators, strain insulators, and dead-end insulators.
• C. Coil insulators, blade insulators, belt insulators, and rod insulators.
• D. Cap insulators, rod insulators, bottle insulators, and cap-and-pin insulators.

Answer: (B)

Overhead lines rely on external insulators to provide electrical isolation while bearing mechanical loads. The main types are pin insulators, suspension insulators, strain insulators, and dead-end insulators. Pin insulators are mounted on a cross-arm pin and support the conductor directly on short spans. Suspension insulators are used in strings hung from a support; the conductor is attached at the bottom, and the string provides insulation and flexibility for longer spans or higher voltages. Strain insulators are placed at points where the line is under high tension, such as near anchors or where the line is pulled tight against a structure, transferring the mechanical load to the pole or tower. Dead-end insulators are used at the ends of spans or at corners where the line terminates, designed to withstand large mechanical forces. These four types together cover the typical external insulation and mechanical support needs for overhead lines.