Frequently Asked Questions about Insulators

New to the hobby? Be sure to read Tedís Top Ten Tips For New Insulator Collectors.

Want to know more about glass making? Read Frequently Asked Questions about Molding Glass Insulators.

Tip: You may also want to consult the Glossary of Insulator Terms.

* What is an insulator?

If a picture is worth a thousand words, you should take a look at a few photographs of insulators in service!

The need for the insulator arose out of the discovery of electricity, which in turn led to the invention of the light bulb, telegraph, telephone, and other electricity-oriented innovations. Also, as railroads began crisscrossing the continent, there came the need for signal devices. Electricity had to be moved economically from one place to another to meet the increasing demands generated by these new marvelous inventions.

According to Webster, to insulate means "to separate or cover with a nonconducting material in order to prevent the passage or leakage of electricity, heat, or sound." 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:

  1. it must be made of a fast-drying nonconducting material
  2. it must be able to hold the line wire in place
  3. it must stay on the pole

This "something" was the insulator. It was developed and improved upon over the years to meet those basic requirements and:

  1. it is most commonly made of glass or porcelain
  2. it has a wire groove to accommodate the line wire
  3. it has a pinhole which fits onto a pin (which in turn is attached to the crossarm on the pole)

* What CD number is my insulator?

Often, one will have to consult the reference books to determine the CD number of an insulator. However, many newer insulators have a style number embossed on them, and one can look up that style number in this Manufacturer and Style Number to CD Number Chart.

* What are the basic groups of insulators?

Pintype insulators are grouped by a number of different characteristics:

There are also non-pintype insulators, which include spools, dead end insulators, and wire strain insulators.

* Why do insulators come in so many shapes?

Insulators were developed over the course of more than 100 years, for a variety of applications including telegraph, telephone, and electric power distribution. Many shapes evolved to hold the line wire more efficiently or to increase the insulating ability. Larger insulators were developed to meet changing needs as larger heavier wires or higher and higher line voltages were used. In addition, some insulator shapes were designed for special applications. Many insulator companies would patent special shapes, designs or other attributes, even if in reality the invention proved impractical. Take a look at some of the varied shapes of insulators.

* Why do insulators come in so many colors?

In general, insulators were not made in specific colors for any reason. The natural materials that were used to make glass, including sand and glass cullet, tended to make light aqua to aqua colored insulators. Some batches were more green, others more blue. In addition, some trace chemicals would alter the color of the insulators. Also, since all glass is produced using some glass cullet, the composition of the cullet would also have an impact on the color of the resultant insulator. Take a look at some of the varied colors of insulators.

* Did colored insulators cost more money?

Special colored glass insulators were produced in only a few cases. A 1909 Electric Appliance Company catalog gives this description:

Special Colored Glass Insulators

Where several lines of different companies are on the same cross arm the lineman can distinguish his line by the color of the insulator. Different currents can also be designated by different colored insulators. We are prepared to furnish all styles of [Hemingray] insulators in red, blue, and amber glass, but shipments can be made direct from the factory only.

Add per M for colored glass . . . . . . . . . . . . . . . $8.00 net

It is interesting to speculate about what was meant by "red" colored insulators, given that "amber" colored insulator are also mentioned. "Blue" colored insulators probably refer to the bright Peacock Blue or the darker Cobalt Blue colors, and not what we call "Hemingray Blue" today.

* How much did insulators cost in the 1900's?

In 1909, prices ranged from $38.70 per 1,000 for No. 9 Pony Insulators (CD 106), to $154.00 per 1,000 for Cable Insulators (CD 257), to $1.00 each for a No. 0 Provo Type (CD 249).

* How much is my insulator worth?

There are many factors that determine an insulator's value. Shape, color, embossing, condition, desirability and rarity all affect its value. Most insulators are quite common and have little monetary value. The first step in determining your insulator's value is to determine which insulator you have. Even with a price guide in your hand, you have to determine which of the approximately 460 shapes, 2800 different embossings, and almost 9000 color combinations best describes your insulator. (And those numbers don't even include any foreign or porcelain insulators!) It is easy to list the common insulators, and also list the very rare insulators, but it is difficult to list all the thousands of collectable insulators that fall between those extremes! A slight difference in the shape of your insulator can affect its value by twenty fold or more. A slight difference in color can also significantly affect the value of your insulator. Unless your insulator is either very common, or very rare, it is best to consult a knowledgeable insulator collector or dealer; or to educate yourself and invest in one of the good insulator books available. If you are serious about collecting insulators, getting a good insulator reference book is a "must".

* How can I add new insulators to my collection?

The two obvious ways to add insulators to your collection are either to find them, or to buy them. Finding insulators "in the wild" can be difficult, and if you find some, there is a good chance that they are common insulators. Most collectors buy (or trade) insulators. Many beginning collectors may find insulators at antique stores, flea markets, and the like, but you will soon realize that your section is very limited, and the insulators are generally overpriced. Although, there is a remote possibility of that rare bargain!

I believe the most effective method to add new insulators to your collection is to obtain them from other insulator collectors. A few years ago, I did an analysis of where we got our insulators from over the previous 6 years. I found about one third of them we bought from ads in insulator magazines, another third from writing for "for sale" lists also advertised in the insulator magazines, and the last third from insulator shows. Not much can top a good insulator show! You get to see a wide variety of shapes and colors, as well as prices! You also get to see exactly what you are buying. It is your opinion of the color, condition and other attributes of an insulator that matters. What better way than to hold it in your hand and look at it? Look at these show listings to see if there are any shows coming to your area. You might also want to check with your local insulator club for additional information. Insulator shows have one other thing going for them -- the people! The people are what make the hobby fun! Meeting collectors and dealers at shows is a great way to learn more and make new friends!

On the Internet, there are a number of insulators for sale pages posted, as well as the Insulator Finder! where you can register your wants and automatically be sent email when insulators matching your wants are posted for sale!

* How can I add a question to the FAQ?

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Last updated Sunday, August 31, 1997