Overhead conductors are supported on the distribution pole using insulators, crossarms, or conductor supports. The National Electrical Safety Code (NESC) establishes the criteria to be followed in the design, construction, and operation of the electric distribution system. The requirements for insulators, crossarms, and conductor supports varies depending upon the grade of construction as defined in the Code.

Insulators. An insulator prevents the flow of an electric current. The insulator supports electrical conductors. The function of an insulator is to separate the line conductors from the pole or tower. Insulators are designed to withstand electrical, mechanical, and environmental stresses. Insulators are fabricated from porcelain, glass, fiberglass, and polymers.

Porcelain insulators are manufactured from clay. Special clays are selected and mixed mechanically until a plastic-like compound is produced. The clay is then placed in molds to form the insulators. The molds are placed in an oven to dry the clay. When the clay is partially dry, the mold is removed and the drying process is completed. When the insulator is dry, it is dipped in a glazing solution and fired in a kiln. The glaze colors the insulator and provides a glossy surface. This makes the insulator surface self-cleaning.

Large porcelain insulators are made up of several shapes cemented together. Care must be taken when cementing the insulators together to prevent a chemical reaction on the metal parts, causing cement growth. Cement growth can cause stresses on the porcelain great enough to crack the porcelain.

Glass insulators are made from...