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Metal Encased Insulators

Metal, although a conductor and not an insulator, has been used in conjunction with insulating materials to make very robust insulators.


Shown is a "Brook's rams horn style insulator.  This insulator was used in the late 1860's and early 1870's and was made from a metal outer case and a metal rams horn with a glass insert cemented between.  These typically were very well galvanized and remain in excellent shape 100+ years later!

Here is another rams horn style.  This version used molten glass as the cement between the outer metal case and the rams horn.  These are known as "Mount Washington Rams Horns" as many were found there.

Here are two cable style insulators that use composition as the insulating material.  (From left to right):

  • Embossed on the dome Westinghouse "W in a circle".  

  • Unmarked -- This insulator is missing the two clamps that attach in the slots at the top.  These clamps will hold the wire over the insulator in the center.

This insulator was used to hang catenary wires and has composition insulation between the outer shell and the wire hanger.

This cable insulator has a metal top and a threaded composition base


A British metal encased porcelain insulator

Another early British metal encased porcelain insulator.

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