A composite line post insulator is a structural insulating component used to support and electrically isolate overhead conductors on transmission and distribution lines. Unlike suspension insulators that allow the conductor to hang vertically, a line post insulator holds the conductor at a fixed angle relative to the pole or tower, making it suitable for compact line designs and situations where conductor movement must be mechanically constrained.

Its primary function is to bear the mechanical loads imposed by the conductor and the environment—specifically tensile, cantilever, and compressive loads—while maintaining electrical isolation between the energized conductor and the grounded support structure. Because line post insulators simultaneously support conductor weight and resist wind-induced lateral forces, their combined mechanical loading is a critical design consideration.

A composite line post insulator is mainly composed of an FRP core, a silicone rubber housing, and metal end fittings. The FRP core provides the main mechanical strength, while the silicone rubber housing with sheds protects the core and maintains good surface performance under wet and contaminated conditions. The metal end fittings are the critical connection components at both ends of the insulator. They are usually made of galvanized steel or aluminum alloy and are attached to the FRP rod by crimping. Their main roles are to transfer tensile and cantilever loads from the conductor to the support structure, provide reliable interfaces for conductor and tower/pole hardware, and seal the rod ends against moisture ingress.