Various forms of third rail insulators

[Trade Journal]

Publication: The Electrical Engineer

New York, NY, United States
vol. 22, no. 431, p. 121-122, col. 1-2,1






THE account in the ELECTRICAL ENGINEER of July 1, of the excellent performance of the cars on the Nantasket Beach Electric road, recently equipped with a third rial, so vividly recalls the use of similar conducting devices in early electric railroad days, that I venture to relate a few experiences with third rails as conductors, in the hope that they may not prove entirely uninteresting at the present time.


This illustration has not been processed yet.


In October, 1883, I equipped 1.25 miles of the main line of the Saratoga, Mount McGregor and Lake George steam railroad, for experimental purposes, with a 35-pound third rail, placed midway between the service rails of the track, and insulated by means of wood blocks which had been thoroughly baked and plunged into boiling pitch while hot from the baking. The foot of the rail was further protected by sheets of soft rubber curled back over the flange and held by square washers under the head of lags screwed to the block beneath, Fig. 1.

The joints were first prepared by thoroughly cleaning the plates and points of contact underneath, when thin sheets of tinned copper were interposed and the joint firmly made up. This did very well for the middle rail, but the service rails were in such bad condition that we found it necessary to adopt some other method, and I finally decided to drill the foot of each rail on one side of the track and run a continuous copper wire with a turn under the heads of special clamp bolts in the newly-tapped holes. From this ground wire and bond combined a few cross bonds were led to the other service and clamped under freshly cleaned joint plates. It only remained to get the deep rust off the third rail, which was done by hanging a heavy board to the motor so that one end would trail on the track, and after attaching a segment of coarse emery wheel to the under side it was duly weighted and towed back and forth until the desired result was attained. The "weight" at first consisted of a 100-pound man, but I regret to add that after a few trips at dead of night our friend failed to find the novelty of the situation a sufficient inducement to continue the exercise, and a resort to inanimate material became imperative. The "collector" consisted of two bronze wheels, mounted on an iron frame in the form of an X, and capable of independent contact with the rail.

The motor ran over the section so prepared nearly every night for two or three weeks with a pressure of 100 to 130 volts, and, contrary to general expectation, the insulation was not low enough at any time to permit of lighting a 75-volt incandescent lamp, In circuit to third rail with line open, except once, when a 10-inch snowstorm was followed by a quick thaw. This rough test of insulation was applied because the use of galvanometer and bridge was difficult on account of strong local disturbances, and the halcyon days of high resistance Weston voltmeters were yet in the dim future.

I think the next use of the third rail in this country was on the Baltimore and Hampden electric road, which was a trifle over two miles long, in 1885. As this was an example of commercial use, having been ordered and promptly paid for in the ordinary course of business, continuing in daily use for four years, practically on the original lines, it may perhaps be deemed worthy of passing notice.