The under-running 3rd rail has one idiosyncrasy that hasn’t been mentioned. The shoe scraper. A 3rd rail contact is an apiece of steel around 1” thick, the rectangular contact area is around 6”x 10” and there is a tapered teardrop to 1” diameter mounting holes around 5” apart on center set 2” from the contact area. The contact is bolted to a pneumatically operated pivot on an insulated beam on the truck. Pneumatic drive solves a lot of insulation problems. A 3rd rail contact shoe must pivot upwards to retract because downwards would put it at or below grade. If a 3rd rail contact, or shoe, is in an intermediate position it could destroy a substantial amount of rail. Before every 3rd rail run where a contact could have been moved there is a blocking plate that prevents a shoe that is neither up nor down from passing. The contact breaks the thin annulus of the mounting holes and falls to the ground. When there were grade level platforms for MUTs all the shoes on the platform side were raised before the platform and lowered after departing. There were always shoes at the scrapers. BTW the broken shoes were useful as a small anvil if the contact didn’t have a lot of wear.

The overhead contact in the GCT approach is indeed for the large gaps in the 3rd rail caused by the switches that allow trains to traverse across multiple tracks. There are at least two full X patterns for both the upper and lower level lead tracks and within some of the platform ladders, The outermost tracks are the only ones that can have a continuous 3rd rail, the center tracks have long voids, particularly at the intersection of the X. A simple turnout style switch can have 100% 3rd rail coverage.

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.

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.

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.

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.

Photo Op? I thought it was Saturday Session Schumer.

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.

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.
http://www.septa.org/service/highspeed/

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.