From Lineman's and Cableman's Handbook, Eleventh Edition

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...

Products & Services
Electrical Insulators
Electrical insulators, high voltage bushings and porcelain insulator assemblies provide electrical isolation of power line conductors in transmission and distribution (T & D), substation, transformer, capacitor and power protection applications.
Silica, Quartz, and Silicate Materials
Silica, quartz and silicate materials include fused silica, quartz, kaolin or clay-based materials, cordierite, steatite, forsterite, sillimanite, zircon, porcelain, and fireclay. They are based on silicon dioxide and various chemical variations.
Electrical Insulation and Dielectric Materials
Electrical insulation and dielectric materials includes various forms of materials that surround and protect electrical conductors and prevent unwanted current flow, leakage or crosstalk.
Ceramic Powders and Precursors
Ceramic powders and precursors contain oxides, carbides, nitrides, carbon, and other non-metals. They are usually micron or mesh-size in distribution. Ceramic powders, sol-gel solutions and precursors are fabricated through atomization, crushing, milling, precipitation, and other chemical processes.
Dielectric Ceramics and Substrates
Dielectric ceramics and substrates are electrical insulators with dielectric strength, dielectric constant and loss tangent values tailored for specific device applications.

Topics of Interest

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5.6 Insulator Design 5.6.1 General As indicated in Section 5.1, it is usual to employ 'pin-type' insulators for distribution voltages up to 30 or 40 kV. Above this voltage and up to about 132 kV...

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