An insulator line post is a stiff, self-supporting insulator. It’s mainly used in medium-voltage overhead distribution systems. It has two key jobs. One is to hold current-carrying conductors in place mechanically. The other is to keep electrical insulation between the live line and the grounded support structure—like a crossarm or pole bracket.
It’s different from a string of suspension insulators. A line post is a single, solid piece. It needs to handle two things. First, bending forces from conductor weight, wind, and ice loads. Second, electrical pressure from the system’s operating voltage and sudden high voltages. Its structure usually has a strong core. The core is often made of fiberglass. This core is sealed and covered by an outer weathershed. The weathershed can be made of polymer—like silicone or EPDM rubber—or porcelain.
The polymer cover has sheds. These are ribs or bumps sticking out. They make the creepage distance longer. Creepage distance is the path along the insulator’s surface. It goes from the live end to the grounded end. A longer creepage distance works better in dirty, damp, or salty places. It stops a continuous conductive path from forming. That path could cause a flashover.
