Insulator Basics!

NOTE: There are links from this page to other independent websites, use the back key on your browser to return to this page

Click this link for information on insulator identification

Insulators were initially designed to insulate telegraph wires. The first telegraph line was built in 1844 and the earliest glass "pin-type" insulators were based on bureau knobs, and over time became sturdier to fit on a wooden pin. These early insulators are known as threadless insulators, as the internal cavity had no threads and was just held to the pin by friction and tar. Even though they were used by the millions in the mid 1800's, virtually all threadless are scarce today, and most are quite rare. Some examples of different pin-type threadless are shown here:

• A Threadless Egg used by the Confederate States in the Civil War
• A Pilgrim Hat style
• A wood covered Wade threadless insulator. The wood provided protection for the glass.
• A Teapot style also used in the Civil War.
• A Bennington Porcelain style in the classic Bennington glaze.
• A Compromise style shortly before the switch to threaded glass.

In addition to threadless glass pin-types, numerous other insulators were developed during this early time. A good article on these is available on-line: Early and Unusual Telegraph Insulators.

Threaded pintype insulators were developed based on a patent (July 25, 1865) by Louis A. Cauvet for internal threads in the glass and a corresponding threaded wooden pin. The Brookfield Glass Company licensed this patent and started making threaded glass insulators. In the 1860's and early 1870's both threaded and threadless insulators were being made by various glass companies.

In 1876 Alexander Graham Bell invented the telephone. This event greatly accelerated the expansion of open wire lines and the need for insulators. During this period, both the Telephone and Telegraph companies started to standardize on certain insulator styles. This is the reason that many different manufacturers made the same style insulators. Even with standardization there were many new styles developed. Most of these were never used in large quantities, but they provide fascination for the collectors of today. A few examples are shown here:

Although attaching a wire to an insulator with a "tie wire" seems like it should be a simple operation, numerous "no tie" insulators were developed to eliminate this step. None of these caught on, and all are rare. Some examples are:

• The Harloe claw has fingers on top to hold the wire
• The Twigg's has a slot in the top which will hold the wire with two marbles!
• The Blackburn Patent has a bail wire like an old soda bottle
• The Buzby has a slot in the top to hold the wire
• The porcelain Purkey Patent has a slot in the top that holds the wire with a 1/4 turn

Another idea was to have the insulator come in contact with the wire as little as possible to reduce the chance for leakage. These styles are also scarce to rare.

• The Chicago Teardrop Pony
• The Cobalt blue Cal. Electric Works
• The Seiler's Patent made by Hemingray.
• The Emminger's

There are also several very odd insulator styles that we are not yet sure of the intended purpose. Some examples of these are:

• The Twin Pin
• The Screw Top Boston
• The Spaceman, an unusual cable power insulator
• The Fred Locke Loop style.

In the 1890's electric power distribution began to grow. Initially low voltage DC distribution over short distances was sufficient. Larger versions of the existing communications glass insulators were initially used with good results. Soon the need to harness hydro-electric power led to much longer distance transmission requirements. Higher voltages and alternating current (AC) would allow low loss transmission and the ability to transform the voltage levels, but greatly increased the demand for high power insulators. Porcelain soon became the primary insulator material for high voltage, with both glass and porcelain being used for lower voltage distribution.

• An early Mershon High Voltage insulator. The ridges on the skirt were to direct water off the insulator to prevent splashing on the crossarm
• A glass Cable Insulator used to carry thick low voltage power cables. This style is known as a Columbia.
• The First Multi-part insulator, A Porcelain/Glass combination. Used at 60,000 Volts in California in 1901.
• A large four piece multipart, made by Ohio Brass.

For additional information on the development of porcelain insulators, see porcelain insulator history.

The information provided here is only a tiny example of what exists in the available Reference Books. I highly recommend that anyone with interest look into these!

Return to the National Insulator Association page

Last updated Sunday, October 4, 1998