22 Responses

  1. Al Cyone says:

    I’ve been looking for just such a thorough explanation ever since news reports referred to an “under-running” third rail. Thanks!

    By the way, I always thought the term “third rail” was a misnomer since, obviously, trains run on just two rails. But from that patent diagram it looks like the third rail was an actual rail. I can understand how that would be economical but were (are?) rails really used as the “third rail”? It seems to me that what you want in a rail (strength) isn’t necessarily what you want in an electrical conductor (conductivity).

    • Emily says:

      Yeah, it is definitely a rail. Check out the photo of Vienna’s third rail which gives a really good look at it.

      • William Hays says:

        Looks rather expensive, compared to the Wilgus system. Think of all the beer cans they could make with that aluminum.

        • cse1024ca256@yahoo.com says:

          Most modern 3rd rails are hybrid aluminum and steel construction. Steel for wear and contact surfaces, and aluminum for conductivity. Considering that Aluminum is more reactive than steel (iron), the low-conductive oxide layer builds rapidly, and will result in frequent repetitive passivization via oxidation cycles whenever a train with 3rd rail shoes passes over. This may lead to rapid wear on both the shoes and the rails, and generate significant amounts of abrasive aluminum oxide dust. It may also lead to greater electrical losses, as the current must flow through partially broken layer of aluminum oxide whenever a train passes.

          Additionally: Aluminum is softer than Iron, thus exposed aluminum wears more readily. Aluminum Oxide is harder than Iron Oxide, thus 3rd rail shoes wear faster.

          • Keith Forman says:

            Actually, modern 3rd rails are aluminum with a wear resistant stainless steel contact cap. NYCT 2nd Avenue will use a 6000A aluminum stainless steel 3rd rail at 1/3 the weight and 40% of the resistance of traditional 150lb steel rail commonly used by NYCT. Its easier to install, does not wear like steel or steel/aluminum rail and is more efficient as a conductor (saves $.) MNRR’s Park Ave line will be converted to this rail in the near future. Throughout Europe, Asia and the Middle East, aluminum stainless steel 3rd rail is the standard. The US has been slow to adopt this technology.

    • William Hays says:

      The ‘third rail’ rail is an “I”-rail, as opposed to the “T”-running rails. It is steel, for economy vs. copper/brass, and much lighter weight. With the DC system, sub-stations are not far apart and conductivity is not a big factor. On the NYCentral system, they were covered by milled wooden insulation (now plastic) and normally wouldn’t ‘zap’ you if you stepped on them (not recommended). Sometimes miscreants drove nails through the wood. Not nice, but the DC would repel you. Doing the same, with an AC contact, would weld you to it. That is why the AC systems were suspended in overhead catenary, away from trackworkers and trespassers. The DC systems operate on +/- 750 volts. The AC systems at 11,000-15,000 volts.

      • William Hays says:

        Addendum/correction: some DC systems used catenary/overhead. City street cars and interurban railways come to mind. The Milwaukee Road (CMStP&P) electrified its Pacific Extension (two segments) with 3,000V DC overhead, and its Great Falls (MT) Terminal with 1,500V DC catenary. Butte, Anaconda & Pacific (MT) electrified with 2,400V DC overhead. Some city streetcars, notably in New York City, used a center-of-track ‘third rail’. Current was picked up by a ‘shoe’, riding in a slot between the rails, under the pavement.

        • Emily says:

          I believe the specific type of third rail that everyone flipped out about in CT was center track too.

          • William Hays says:

            Interesting factoid: NYC’s Third Avenue Railroad had transition points, from overhead trolley to center third-rail pickup shoes/plows. They had a dugout/foxhole/observation room, under the street pavement. A guy sat there and made sure the “plow” properly engaged the subterranean power rail. Cool job, no?

        • Matthew Holbrook says:

          The Delaware, Lackawanna & Western Railroad (DL&W) also used DC current at 3,000 volts to power its New Jersey suburban services from Hoboken to Montclair, Gladstone, and Dover, NJ. This electrification was in daily service until August of 1984. Thomas Edison was reputed to have led the first electric train out of Hoboken in September 1931. Hence the trains were affectionately known as the “Edison electrics” until their retirement in 1984. I rode on those trains as a child in the 1970s.

    • William Hays says:

      A bit off-topic, but another kind of third rail was used, that being dual-gauge trackage, where two different gauges met ( eg. a standard gauge [4′-8.5″] and a narrow gauge [3′-0″] converged. One of the three rails was common and the other two offset the appropriate distance. Sorry for the babbling. ‘Cabin Fever’ has set in!

  2. Phil Moberg says:

    Thanks for spreading the back story of the third rail beyond the community of historians and fans. There was a second Philadelphia property – the Philadelphia & Western – built with Wilgus third rail, and the Central California Traction also used it. The former converted to overrunning third rail, and the latter dieselized.

    • Emily says:

      Thanks much! I knew there were definitely some others out there that used the Wilgus/Sprague method!

    • Lee says:

      The P&W did start with under-running third rail and converted to over-running. However, it never went diesel, and uses electric cars to this day. It is now known as SEPTA’s Norristown High Speed Line.

      The third rail on SEPTA’s Market Frankford Subway Elevated line is under-running, while its Broad Street Subway is over-running. The subway-surface trolleys use overhead wire and trolley poles.

  3. T Man says:

    I was on the Century of Third Rail tour, the last “true” group tour that MN has done. Great to see the underpinnings of the power infrastructure. Even got a small piece of the third rail as a memento.

    Of course you are correct. This driver was at fault.

  4. William Hays says:

    Very well done, Emily! Beware Charles “Chuck-the-Schmuck”/”Photo-Op”/”Chuckie ‘Say Cheese'” Schumer! He won’t like you! Don’t leave your camera at home!

  5. Steve Dunham says:

    Good job. I learned a lot.

  6. Ellis Simon says:

    Very informative post, Emily. The early New York Central electric motors, i.e. S-class, had small pantographs in front of the cab. Can you confirm whether these were used to draw power from an overhead rail when locomotive-hauled trains passed over the switch clusters leading to GCT?

    • Jackie Kaplan says:

      You are correct. The throat of Grand Central had overhead rail (not wire) installed to make up for gaps in 3rd rail necessitated by the switches. New Haven electrics, and even their first order of dual-powered FL-9 diesel locomotives also had small DC pantographs.

    • Jackie Kaplan says:

      That is true. The New Haven electrics and even the first 30 FL-9s had such pantographs as well. Multiple unit trains didn’t have them as they assumed at least one car would always have power (but they had a gizmo to electrify trains which did loose all electric conntact. Interestingly, the overhead catanery in GCT is rail, not wire. I’m not sure if the catanery still is in place–only a few trains are pulled by FL-9-type locomotives.

  7. David Levy says:

    As a kid, I was taken to the Russian (Soviet era) exhibition at the NY Coluseum at Columbus Circle (no longer extant). There was a cutaway display of the Moscow subway, and I noticed that the Moscow Subway, too, used underrunning third rail. I imagine it still does, since a changeover to overrunning would be costly and would seem to have no purpose.

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