Strain insulator

A strain insulator is an electrical insulator that is designed to work in mechanical tension (strain), to withstand the pull of a suspended electrical wire or cable.

Strain insulators were first used in telegraph systems in the mid 19th century.

A typical strain insulator is a piece of glass, porcelain, or fiberglass that is shaped to accommodate two cables or a cable shoe and the supporting hardware on the support structure (hook eye, or eyelet on a steel pole/tower).

In practice, for radio antennas, guy-wires, overhead power lines and most other loads, the strain insulator is usually in physical tension.

This setup is almost universally used on long spans, such as when a power line crosses a river, canyon, lake, or other terrain requiring a longer than nominal span.