Communication and electric line wires in service must be kept as dry as possible in order to function efficiently, and to cut down on loss of current. The wires are kept off of the ground by being strung between poles. But something was needed to keep the wires and (sometimes wet) poles apart. This “something” had to meet three basic needs; it must (1) be made of a fast-drying non-conducting material, (2) be able to hold the line wire in place, and (3) stay on the pole. The insulator was developed and improved upon over the years to meet those basic requirements; it is (1) most commonly made of glass or porcelain, (2) has a wire groove to accommodate the line wire, and (3) has a pinhole which fits onto a pin (which in turn is attached to the cross arm on the pole.)
The more insulation between the pin and the pole, the better. To create a longer distance between the two, and to cut down on loss of current, many insulators have one or more “petticoats". The petticoats increase the linear distance measured along the surface of the insulator between the pin and pole, and improve the efficiency of whatever service is being provided by the line wire. The skirt of an insulator is also considered to be a petticoat. Therefore, insulators like the one in the sketch are called “Double Petticoats.”
Some Insulator Color-name Explanations
Carnival Factory - applied outer coat of Tin oxide.
Flashed Amber Factory - applied outer coat of amber color.
Swirls/streaks - Pronounced or contrasting amber, milky, or other colored swirls or streaks in the glass.
Jade Milk - Less pronounced, more thoroughly mixed "milk,' throughout blue green glass, giving a clouded effect.
SCA - Sun-colored amethyst or light purple, which may or, may not have been caused by exposure to the sun.
Snow/Bubbles - Tiny/larger bubbles throughout the glass.
Insulator Classifications And Materials
Insulators can be classified into nine basic groups; Glass, Porcelain, Non-glass-Non-porcelain, American, Foreign, Uni-part, Multi-part, Threaded, and Threadless (Non-threaded.)
The first three groups refer to the material of which the insulator is made.
"Foreign" means any insulator not used on the North American continent. (Mexican and Canadian insulators are not usually classified as foreign.)
"Uni-part" means any one-piece insulator;
"multi-part" means any insulator of two or more separately molded parts, either cemented together after manufacture, or used together on the line.
"Threaded" means any insulator with internal threads which correspond to matching threads on a pin;
"threadless" means any pin type insulator without threads and having a smooth pinhole; (not to be confused with spool-type insulators.)
A few materials of which insulators have been made include glass, porcelain, wood, rubber, polyethylene, plastic, fiberglass, and composition. (We will deal with just glass insulators.)
To some, the purpose of insulators might seem quite obvious, but to others it isn't. So it might be a good idea at this point to give a simple explanation.
According to Webster to insulate means: "to separate or cover with a non-conducting material in order to prevent the passage or leakage of electricity, heat, or sound." An insulator is a device used for insulating and supporting wires for electric, telephone, telegraph, and railroad signal lines.
