I was on Metro North and noticed that they use a under the rail collection system and today on PATH I noticed that they use a over the rail shoe…One could geek out on the reasons why so what the heck lets do it!
Under the rail collection gives better protection from icing (which is a big problem on systems where the pickup shoe runs on top of the rail - BR used to operate deicing trains in an effort to avoid this) and also allows you to shield the rail more effectively - you can box it in more so that anyone unlucky enough to fall on it runs less risk of electrocution. Those are the main reasons I can think of anyway!
Well, the underrunning third rail used on Metro North does pretty well, except when it snows in some quantity. Much of their third rail in stations is covered by wooden guards, which are not 100% effective, like when there are repeated freeze and thaw and re-freeze cycles. On the whole, William J. Wilgus, NYC&HRRR’s chief engineer did rather well (rather?)-it’s over a century old and it works well enough since there has been no serious consideration undertaken with regard to changes in the power distribution or third rail systems since! New Haven, Westinghouse (straight Electric “motors”) Alco,GE and Ingersoll-Rand(Tri-power units) and GE on its own (straight electrics and dual modes for Amtrak and M-N) as well as EMD (FL9s) had headaches with the need to mix 11Kv AC and 600v DC in one unit,or 600 volt DC from a limited amperage source and an unlimited (for 1.75 seconds, at least) amperage source, but the FL9s lasted almost a half century as did early NH straight Electrics. The NH’s management shot them selves in the foot trying to junk electrification, otherwise the EP2s,EP3s, and saddest of all, EP4s and EP5s might have run for that long, too! Now, PRR and Long Island did not have to worry about weather exposure, since their over running third rails were mostly in tunnels and under buildings built on air rights, until LI expanded its electrification out to Nassau county points. Then real headaches result during and immediately after any noticable accumulation of snow or ice occurs! Then, trains run late, if at all. Both systems tend to lose contact with trains if they are bouncing around on uneven trackage, unless there are a sufficient number of contacts (Third rail shoes) far enough apart to minimize disruptions. However, in my experience there almost always was a brief power outage from time to time, when contact with the power source was lost. Momentum kept things moving,but if it happened at a stop, then a “rescue locomotive” or car had to be sent out to get the “victim” moving,lit and heated/air condit
As far as contact there is not a lot of difference. They are both spring loaded to adjust for height differences and the shoe is replaceable.
Overhead wire freezes too. Cleveland RTA runs a late night deicing train in bad weather
the overrail collection systems that I have seen look to have simpler mounting systems for the 3rd rail than the underrail systems
dd
Mr Benham MNCR has not had wooden guards since 1984, all third rail including inside GCT has plastic sleeves over the top.
The sleeve has nothing to do with sleet or snow but is just protection vor workers stepping over third rail, there is no requirement at all by law to cover third rail.
And despite the NYC system third rail originaly 600 volt it is now 750 volt DC nominal.
Most rapid transit systems use overrunning third rail with gravity used to maintain contact. While icing can be a problem, most transit systems equip their cars with sleet and ice breakers to deal with it.
As far as getting stranded in a dead zone, CTA and other systems use a stinger, which is two contact poles connected by heavy cable, as a jumper to get power from the third rail to the stranded equipment.
CTA uses the gravity third rail shoe, and it was the standard for both Manhattan and Brooklyn Elevated Railways (Manhattan = Manhattan & The Bronx). But the Interboro Rapid Transit, the Borrklyn Rapid Transit + New York Municipal Railway (later the BMT), the Long Island Rail Road, and the Hudson and Manhattan (now PATH) and the Pennsylvania for its initial Penn Station electrification, adopted an overruning third rail further from the running rail and slightly lower, and used and use spring shoes and not gravity. The overruning third rail on these systems is and was compatible and was also adopted by the city’s Independent Subway, first line opened in 1932. BMT and IRT subway cars had shoes with two contact and wearing surfaces, the outer for normal use and the inner for contact on lines still using elevated type third rail. IND third rail shoes generally lacked this feature.
It’s interesting that in all these very informative discussions of heavy and commuter rail current pickup systems, nobody apparently knows or cares about the former B&O/Staten Island Rapid Transit Railway, now part of NYC Transit. They use over-riding third rails.
Rode it during the first fifteen years of my life.
What surprises me greatly is that CTA has NO guards over their third rails, at least on their overhead lines.
The london underground has under and outside shoe
Here in Australia where we don’t have any 3rd rail electrification it looks pretty dangerous to work around. As a signal maintainer I wouldn’t want to work around live 600-750v at ground level. Is the 3rd rail isolated near train stops etc that need repair under traffic? As that would put a track out of service while maintainers have possession the disruptions must be considerable.
I read that in 1947 California banned exposed 3rd rail on open track, leading to Central Cal. Traction and Sacramento Northern ending electric operation, at least on the old Northern Electric part of SN. This was after a child was electrocuted near Woodland, and I also believe a child was electrocuted on the day the CA&E “temporarily” suspended service in 1957. I suppose the Key System Bay Bridge track was considered adequately separated from the public under the law.
The old North Shore Line ritual of raising and lowering trolley poles at speed and then throwing an open knife switch for the change-over, must be one of the toughest stunts regularly performed as part of a day’s work . Imagine hanging out the train door at the back of a speeding interurban, trying to land the pole on the wire in the dark, during a blizzard. Imagine doing it for the first time.
But the most ironic thing I see about 3rd rail is most of it is in places where snow and ice abound in winter, which must cause tracking of current over insulators if de-iced with salt. Still, it’s been around in one form or another since the 1890s so it must work well enough not to change, and new systems are still being built with it, so it won’t go away soon. And the world wouldn’t be as interesting if everything was done the same everywhere.
In fact the London Underground uses 3rd and 4th rail with the outer rail at +375 V dc and the inner rail at -375Vdc. The advantage of this, compared with 3rd rail is that the current finds its way back thru the inner rail, otherwise it would just find its way back thru the earth (as in conventional 3rd rail) which could be inconvenient, particularly underground!
To answer Tony G’s questions - yes 3rd rail is potentially dangerous, but provided people are made aware of the dangers accidents can be avoided. At foot crossings gaps are provided; also on some of the more recent 3rd rail schemes in Britain research has been undertaken to ensure gaps are provided at locations where wild animals such as badgers cross the line to reduce the danger of them getting electrocuted. (In Britain we have a lot of 3rd rail electrification - in the 1920’s and 1930’s the Southern Railway electrified its extenstive commuter network in South London on this system and the main lines from London to Brighton and Portsmouth. Since then the mainlines to Bournemouth and the Kent Coast ports have also been electrified.)
Most 3rd rail EMU’s have plenty of picks up shoes to avoid getting gapped. Back in the 1940’s and 1950’s the Southern third rail electric locos were provided with flywheels to power them over gaps in the 3rd rail. These locos have now been superceded by hybrid electro-diesel locos which have a 600hp diesel engine to power them off the 3rd rail in sidings.
[quote]
Originally posted by the feed
The london underground has under and outside shoe
This system of a “centre point earth (or ground)” used in London was used many years ago in Sydney on a short tramway from a railway station called Rockdale to a resort hotel on Botany Bay called Brighton-le-Sands (these promotors have such an imagination for names). Originally steam operated, with an 0-6-0T converted to a 2-2-2T by removing the side rods (!), it was electrified in 1900. It had a large motor car and trailer that shuttled back and forth, the trailer being propelled one way, hauled the other. The motor would also haul coal cars to fuel the power house for the tramway and hotel, which had two 250vDC generators, with central earth point between them, connected to the rails.
These generators fed twin-wire overhead with 500v potential between them but each 250v + or - from the rails. Thus two 250vDC circuits were available for domestic power from the power house as well.
The motor car had twin poles, side by side and trailed one way and speared the other, as they couldn’t be turned. The line was only about 1 1/2 miles long. This curiosity lasted until 1914, when the line was taken over by the New South Wales Government Tramways, the main Sydney tramway operator, and converted shortly after to conventional 600v operation, with the second trolley wire retained as a feeder. The oddball motor and trailer were scrapped, and the line operated with what passed as conventional Sydney cars (70-seat crossbench maximum traction cars) till 1949.
Today buses run on exactly the same route, demonstrating the flexibility over rail transit that makes the bus so superior.
Going back to Pauluhland’s earlier comment about CTA and 3rd rail guards/covers, you can’t have a cover with the gravity-type shoe, as it rides directly above the third rail and the support beam for the shoe is above that.
Slipper type shoes, which were spring-loaded, and therefore didn’t have the whole support beam directly above them were used on the 6201-6510 and 2201-2350 series CTA cars. The slipper shoe is not favored on CTA, as only 2200s remain with them, all cars bought subsequently have had the gravity shoe design.
CTA has equipped several passenger cars to distribute sleet/de-icing paste to the head of the third rail (the cars have additional on-board equipment and other provisions to support this use, when needed). The AC cars (currently in the bid process) are all to come with the equipment to facilitate sleet paste distribution.
In the past CTA used dedicated “snow fighters” (converted 4000- or 6000-series passenger cars) to spread de-icing paste, plow bigger drifts, if they had formed. There are now diesel-powered snow fighters asssigned to each major terminal, which can be used to clear yard or mainline tracks if the need arises.
Going back to the London Underground. The double power rail system makes a great deal of sense, in spite of the extra expense and maintenance. In almost all electrification schemes except that, the running rails form the return (earth) circuit. There are two interesting problems: signaling becomes somewhat more complicated, for one, but the other is more subtle. Electricity is exceedingly lazy, and if the joints in the running rails aren’t perfectly tight, the current will move off the running rails and into any other nearby wires, pipes, or what have you. Not a shock hazard (usually), but it can create noise on telephone lines, and unbelievably rapid corrosion on buried pipes. Instant leaks…
So as understand it if one has thick rubber shoes and ONLY touches the third rail there is not a complete circut?
In toronto and on some people movers dont the use a lineir unduction collection system?
On the Buffalo and Rochester Interurban they used third rail ont in the country and overhead wire in the city
A bit more info on the London Underground 4th rail system here - http://www.tfl.gov.uk/tube/using/useful-info/technical/electricity.asp (note it’s actually a +420/-210 volt ‘floating with respect to ground’ system).
On the extensive 750v 3rd rail system in southern England, there are usually wooden boards on both sides of the conductor rail in areas where staff might walk e.g. yards, stations etc. to provide some protection against accidental contact. Also the conductor rail can be installed on either side of the track, so it’s generally placed on the side where people are least likely to touch it.
Correct - that’s why birds can happily perch on 400,000 volt power lines [:)]. But always be very careful around high voltage electricity - at the very least bad electric shocks are unpleasant and can easily be fatal.
Tony
Look up and you could see some other type of electrical distribution to trains: the overhead wire catenary. This is above the ground and virtually eliminates the possibility of electrocution from stepping on a rail. Watch out for cranes. If they hit the overhead it will trip the circuit breaker in addition of sending the crane operator to the laundry. A different tact to this is where both the power and return/ground are overhead. Think of the trolley buses that still exist in some cities. Rubber tires are a very poor electrical conductor so an overhead return is manditory. There are a couple of other examples of where this was used. I think it was Cincinati (sp?) that had overhead returns for their street cars early on. At that time the telephone company used the ground for their return circuit and the street cars caused interference with the telephones. Guess that people were more enamored with the telephone than the trolley so the trolley had to have an overhead return. Politics again. Another example of dual overhead lines was in the Cascades with the NP or GN (cannot remember which) had two wire system. They did this because they were running three phase AC system and it took the third wire (counting the rail return). At that time speed control od AC motors was non existant so by having the three phase system they had 2 or 3 potential speeds. AC has better transmission properties than DC hence less capital investment for substations and line loss. The down side is the inability to control speed. This was solved with the electronics available today. There was some exotic wire assemblies where there was a branch (switch) in the trolley bus route. I remember seeing an electrical spark show when the shoe traversed the overhead line switch setup.
Italian State Railways (FS) also used the 3-phase AC double overhead system in the northern part of the country. It was eventually replaced. An article in a 1962 issue of TRAINS describes the Italian network nicely.