The Patent Office

Reprinted from "Crown Jewels of the Wire", May 1989, page 17

THIRD RAIL INSULATOR
Patent No. 628,667 dated July 11, 1899
by Charles King and George Mead

In the early 1970's, Carol and John McDougald found two unusual insulators at a flea market. The owner said that both were found in the same pole hole where someone had pitched them. One looked like a third rail insulator and the other was a very crude three piece cable-top. Both were made of the same type of stoneware (not porcelain) with a transparent, shiny glaze. We will show the cable-top insulator in this article since it was found with the third rail insulator and is made of similar material.

The cable-top unit is pictured below and at the top of the next page. You can see that it is very crude and made up of three nested shells fused together. There are still traces of cement on the bottom of the insulator where it may have been cemented on the underground vertical walls of the tunnel under the rail. This insulator was probably used to carry the electric feeder cable. Notice the large damaged area on the outside skirt which was made before being glazed and fired. The whole body seems to sag as if the clay had been much too wet when it was made, leaving no good means of securing the tie-wire to the crown. This must have been the cheapest insulator available.

The third rail insulator pictured below is made of similar stoneware and glaze, but the construction is of much better quality. There is a horizontal groove around the top with a vertical groove on opposite sides of the top which intersects the horizontal groove. This horizontal groove is not a tie wire groove as can be seen in the patent description (see end of this article).

The metal cap held the electric rail and had two lugs which fit into the vertical and horizontal grooves. By turning the metal cap 90 degrees (where the cap lugs would be halfway between each vertical groove), it could be snugly locked in place on top of the insulator. The pinhole of the third rail insulator is threadless with two opposite vertical grooves which intersects a horizontal groove near the top of the pin hole. A pin with a horizontal lug was used to lock the insulator in place. The patent describes these features in detail, so I am sure that this insulator was made with the patent claims.

Both insulators are unmarked. The manufacturer of the cable-top insulator is still a mystery, but I believe that the third rail insulator was sold by Ohio Brass. What, you say, was a porcelain company doing making insulators of pottery? Well, the answer to that question is open to speculation, but I would guess that the answer may be found in the strength needed for that severe service and the close association Ohio Brass had with Akron High potential. Third rail insulators take a lot of abuse from vibration as the train passes over the rails. The job of the insulator was, of course, to insulate the electric rail, but, in so doing, it had to be very strong to hold the steel rail in place.

Ohio Brass was associated with Akron High potential, possibly from the very beginning of Akron when they were formed about 1900 (recall the patent date is 1699). Akron initially manufactured general ceramic products (!) and entered the manufacture of wet process porcelain pin type insulators sometime between 1903 and 1905 (info from Jack Tod's new book, Porcelain Insulators Guide Book). 

In the Ohio Brass catalog (actually Akron's production of pin types) dated 1907 (see the photo below), this same third rail insulator was shown as "Type A - Form 1". The catalog described the insulator as being made of "Semi- Porcelain" and being "highly glazed"; and the catalog noted that the insulator was "patented". The Ohio Brass catalog dated 1914 shows this same insulator, but describes it as a "Porcelain block" -- it was now made of porcelain.

Possibly by 1914, Ohio Brass (having purchased the Akron plant in 1910) was able to manufacture the third rail insulator using a stronger form of porcelain than was available earlier. It is conceivable that Akron was not able to produce strong porcelain during the those early years and used instead their "general ceramic" technology. Consequently, I believe that this third rail insulator was manufactured by Akron High Potential for Ohio Brass circa 1900 to 1910. I have seen one other identical third rail insulator in Jerry Turner's collection. No other cable-top insulators, as described earlier, are known to me, and this one may remain a mystery.

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