Insulator Types
by Greg Kareofelas

Reprinted from "INSULATORS - Crown Jewels of the Wire", February 1970, page 3

Few people realize the part insulators played in the development of the communication and electrical systems we have today. The start of the electrical age created the need for insulators, a device to prevent the leakage of electron flow from the wire or circuit carrier. Insulators also provided the means of securing the wire to a pole, house, tree, etc. Modern technology and plastic insulation has all but replaced the need for glass and porcelain insulators, but because there were so many made, insulators will be around for many more years. Unfortunately, few collectors anymore have the opportunity to observe insulators actually "insulating". The purpose of this series of articles is to give insulator collectors insight into the various settings that insulators were created for and the variety of functions they served. This article will be a general survey of insulators, broken down into major categories by type and function. More specific articles will follow in which these groups will be investigated in greater detail.

We will start by examining the first major group: Communication Insulators made of glass. Communication circuits are of low voltage, hence the insulator needed must be relatively small. A wide variety of styles of communication insulators have been produced over the last hundred years, most having one groove and a single petticoat. Figure 1. lists a few of these types.

Many special types of communication insulators were created for specific purposes. For example, when two wires run parallel over a long distance "cross talk" was produced. It was found that this interference could be eliminated by transposing the wires. A transposition insulator was designed for this purpose. Transposition insulators have two grooves and have been made both single and double petticoat.

The Brown pony was an insulator designed to double the carrying capacity of a cross arm. They were patented-by Mr. Brown in 1886, but evidently were not too popular for they are not very common today. Brown ponies needed a special pin to be used properly.

In addition to the normal groove, the double groove pony was provided with an additional wire groove on the lower skirt This was for holding the service or drop line mounting.

A top groove insulator, as its name implies, has an extra groove on the top. This insulator was for use in hilly or mountainous country where a top tie provided a much more secure mounting.

Mine insulators were used to take electricity or communications deep into a mine. A special pin was driven into the rock or beams in the ceiling and the insulator screwed on. The threaded hole in a mine insulator, went all the way through.

It was found that porcelain provided an effective insulator, so many of the above types were also produced in porcelain. These are usually glazed a dark brown color but reds, blues, and whites are known. The threads in a porcelain insulator are the same as those made of glass.

Another style of porcelain insulator commonly seen is the familiar white "knob". Many sizes were produced to satisfy a need for a cheap, easy to install, insulator for low voltage. Many rural lines, still in service, use this type of insulator. They were mounted by driving a having a leather washer through the central hole.

Power insulators were used in the distribution of electrical power from the generating source to the ultimate consumer. Large suspension insulators are familiar, seen hanging from large steel towers.

Large porcelain insulators mounted on tall poles are also well known. Large glass types were made too, but are rarely seen in service at the present time. The use of double and triple petticoats is common on these large insulators. This feature enabled the insulators to carry a large current more efficiently. A longer path of resistance was created by these petticoats and they also provided a dry space when it was raining. Another feature of high voltage insulators is the wider groove for the larger wires that had to be carried.

Intermediate, or secondary power distribution insulators are not so large, the amount of current carried having been transformed down. These types have the groove either on the side or on the top, and have been made from both porcelain or glass.

The power poles outside your home have small power insulators such as these, again made from either glass or porcelain (fig a). The service lead, from the pole to your house, usually ends up tied to a small porcelain insulator mounted on a galvanized frame (fig b).

In the past, before the invention of dependable insulated house wiring, small porcelain insulators were used in wiring homes and buildings. These were mounted to rafters and wall studs by nails and held the wire by compression pressure.

Certain types of insulators were created especially for use in localities where there were many trees. The Cutter Tree Insulator was probably the earliest type, having been patented in the mid 1800's. The split porcelain type is another example of an insulator for use forested areas. The two halves were assembled with the circuit wire in the center, a binder wire wrapped around it, and then anchored to a tree. These are still very common in the forested regions of the west.

Strain insulators were used to insulate the support or guy wires used in communication or electrical construction. Small types were used to make a dead end or stop. The earliest types were made of glass, but all modern types are made of porcelain.

It is hoped that this article has stimulated some interest into the actual setting that insulators existed. It is fun to collect insulators for there color or shape, but as collectors, we should have some idea as to the reasons the colors and shapes were created. So, before you pull that next insulator off the pole, examine how it was mounted and pay attention to clues as to the actual function it was performing

Written by Greg Kareofelas, co-author (with Gary Cranfill) of "The Collectors' Guide for Glass Insulators"
 with prices revised, also "The Dictionary of Glass-Ceramic Insulators Reprint."