Talk:Third rail

From Wikipedia, the free encyclopedia

Trains Portal

This article is within the scope of WikiProject Trains, an attempt to build a comprehensive and detailed guide to rail transport on Wikipedia. If you would like to participate, you can visit the project page, where you can join the project and/or contribute to the discussion.

[edit] North London Line

1) Is it really true North London Line trains have to change their power supply mode several times? The line is, as far as I know, on some parts electrified with third rail and with overhead wires, thus each type of train can go through without problems.

2) In its part south of Thames it shares tracks with the District trains. The line has a four-rail electrification. How do the mainline trains manage if the positive rail is just +420 V? Can they use the forth rail? Is it the same in case of Euston-Watford trains when sharing with Bakerloo?

Electroliner1 19:53, 15 November 2006 (UTC)

First of sign your comments by pressing the tide key "~" 4 times ;)

The NLL uses OLE (25 KV AC), and third rail (IIRC both LUL style 4 rails and "normal" third rail). Have a look a the NLL article and also Railway electrification in Great Britain. Also have a look at this website [1]. If I've got it all right the LNWR's suburban network was 4 rail electrified but i think the current rolling stock (313 EMUs IIRC). Large parts of the central, NLL section was OLE'ed for eurostar access to North Pole depot (off west London line). Now the lines beyond where broad street station was (Dalston junction) weren't part of this initial electrification scheme. This site [[2]] says that the rest of the line to north Woolwich was 3rd railed in 1985 so they could close broad street. I think the lines which don't run LUL stock don't have 4 rails as 313s don't need to use the 4th rail as the earth (they use the running rails) - I'm no electrical expert but there is writing on this matter around the net.

In answer to your second question, is i think in my reply to your 1st - mainline trains are 313's (i don't think Southerns 377s West London Line service to Watford Junction uses any of the lines you are questioning) and don't need the 4th rail, and the power supplied on the energised rail of the 4 rails system is enough to propel them. there is a bit about voltages on the shared bakerloo line and Watford dc line in the Railway electrification in Great Britain article.

Hope that helps Pickle 20:00, 16 November 2006 (UTC)

Thank you very much for responding. Actually, I didn't know how it works with the signatures; hoped it would be signed automatically.

So, it all seems to have changed significantly with the access of 'Eurostars' to the North Pole depot. Previously, as my references show, the third rail continued between Camden Road and Acton Central, which made dual-system trains unnecessary on the North London Line. It that correct?

However, it is the four rail system that exists from Gunnersbury Jnct. to Richmond. It may even be seen on Google Earth. I suspect the powering is similar to that of the Watford Line. That is 3rd rail c690V DC, while the 4th rail - zero. If I have understood you well.

Electroliner1 09:34, 17 November 2006 (UTC)

I'm not 100% certain but most if not all the OLE work (25 Kv AC) around the NLL was for Eurostar access to North Pole (from the CTRL/HS1 line at St Pancras) in the early/mid 1990s, it also may have a lot to do with the abandoned regional eurostar plan (GNER used some of these 7 car sets for a bit) which would have seen eurostars on lines like the GWML, WCML, MML, ECML and even GEML (i think). However upon consulting a map ( [3] - have a look at the other UK maps on this site [4] ) its only OLE between Acton Central and Camden. There are dual (ie third and OLE) sections from there to St Pancras and Dalston Kingsland to Stratford. As i said above I'm no sparky and the exact technicalities of how the voltages work to me is some mystical black art!!! Pickle 14:39, 17 November 2006 (UTC)

Trains running from Richmond to Stratford (Low Level) have to change system a total of four times. Between Richmond and Acton Central they run on 660 V d.c., third rail. At Acton Central, trains change to 25 kV, 50 Hz a.c., overhead. Between Acton Central and Camden Road they run on 25 kV, 50 Hz a.c., overhead. At Camden Road trains change to 660 V d.c., third rail. Between Camden Road and Dalston Junction they run on 660 V d.c., third rail. At Dalston Junction, trains change to 25 kV, 50 Hz a.c., overhead. Between Dalston Junction and Hackney Wick they run on 25 kV, 50 Hz a.c., overhead. Between Dalston Junction and Hackney Wick 660 V d.c., third rail is also installed, but trains do not use it in normal operation. Under abnormal operating conditions, it is used, but the power level of trains must be limited (Notch 2 working). At Hackney Wick trains change to 660 V d.c., third rail. Between Hackney Wick and Stratford (Low Level) they run on 660 V d.c., third rail. --ALECTRIC451 00:06, 1 February 2007 (UTC)

[edit] Advantages expansion

Guys, right now it looks like third rail has minimal advantages and just plain sucks. Since new systems are still being built with it, i'm sure that's not the case, so let's get something out there! lensovet 04:29, 4 June 2006 (UTC)

[edit] Disadvantages - doesn't present a world view discussion

I deleted the language that third rails use "low" voltage. The ones near me have signs that say "Danger 750 Volts." Also, new transit systems continue to be designed and built (e.g. the Los Angeles Metro) using third rail power transmission methods, so it's incorrect to say that the method is obsolete. Mbstone 01:12, 13 Oct 2003 (UTC)

750 volts is a very low voltage in comparison to overhead wires which can carry up to 25,000 volts. Perhaps it would be better to say that it has a relatively low voltage. You've deleted an awful lot of valid content which I'm putting back. G-Man 18:03, 13 Oct 2003 (UTC)

In San Francisco/Bay Area, the bart runs on 1000 volts DC and has a maximum speed of 130 km/h. They continue to expand their system so obviously it's not obsolete. That text needs to be rewritten, and also the whole thing about the shoes constantly falling off seem to refer to one system in the world, the one in the UK. we can't say that it is true for other countries when we don't know this. Lensovet 17:34, August 30, 2005 (UTC)

[edit] The London Underground's third and fourth rails

The article originally stated that the London Underground 4 rail system is isolated from ground. This is completely untrue, apart from being obviously hazardous.

In fact the positive (outside) rail is +420 volts relative to ground. The negative (central) rail is -120 volts relative to ground. This gives 630 volts to the trains' electrical system. The reason for the odd split is unknown at this time.

I'll bet that somebody calculated that that combination led to the fewest problems from stray current leakage and electrolysis, a major pair of problems for any electric railroad.

Atlant 21:26, 26 March 2006 (UTC)

Well whoever calculated, calculated wrong. The voltages do not even add up. 420 - (-120) = 540, not 630.

--Jon Esquivel, 27 March 2006

You're missing my point. (Ignoring the absolute magnitudes of the voltages,) If we assume that the voltages are asymmetrical, this was probably done for a good reason rather than "on a whim". I'd be willing to bet that the "good reason" was to minimize the effects of stray currents and induced electrolysis system-wide. Seriously, this has always been a major design concern for electric railroads. Not only are they trying to maximize the life of their own equipment, they're also trying to be good neighbors. It's always the sign of a big problem for them when, for example, the water company calls up the subway company and tells them that they've just discovered that there are 200 amps flowing in the water company's iron piping, and the current flow is corroding things to hell.

Atlant 12:50, 27 March 2006 (UTC)

It was a typo. The "-120 volts" is supposed to be -210V. Now the voltages are consistent.

The outside (positive) rail is higher off the ground, and thus better insulated, than the central (negative) rail. To distribute the stray current leakage evenly between the rails, the voltages were set proportionally to the rail-to-ground resistances (a two-thirds/one-third split).[5] Opie 14:00, 27 March 2006 (UTC)

[edit] Dying to go?

Actually, the urban legend is true and I have found actual examples from both NYC and other areas. That is why the original article that I researched called this a 'true urban legend'.

From The Straight Dope column by Cecil Adams:

Dear Cecil:

Are there any known instances of winos, derelicts and others possessing unreliable bladders meeting their Maker while peeing on the third ("hot") rail from a subway or elevated train platform? --Impatient on the Howard line, Chicago

Dear Impatient:

Not in Chicago. But I did turn up one instance in New York City, ever the pacesetter in this regard.

Marshall Houta's Where Death Delights contains the sad story of one Joseph Patrick O'Malley, a man with two unfortunate habits: heavy drinking and wandering through subway tunnels.

One morning, O'Malley's mangled body was found in a tunnel 50 yards from the nearest station. He had apparently been struck and killed by a train.

But an autopsy turned up another cause: "The burns on the head of the penis and on the thumb and forefinger were obviously electrical burns....The stream of urine had come into contact with the 600 volts of the third rail. The current had coursed up the stream to cause the burns on his body as the electricity entered it.

"In all probability, he was dead from electrocution before the train ever hit his body." Mbstone 01:47, 13 Oct 2003 (UTC)

"There are unverified reports that people have died as a result of urinating on the third rail, the urine stream completing an electrical circuit that results in the victim being electrocuted."

On the Mythbusters TV show, they tested this as best they could (using a dummy, and urine). IIRC, the only way they could electrocute their dummy was by using a huge (1" diameter or so) stream -- urine (at the rate it leaves the body) simply doesn't form a constant stream all the way to the ground, so there's no way for the electricity to travel through it. Maybe if you got really really close.

[edit] Maximum third-rail voltage?

I read the maximum voltage for a third rail is around 1500V, but I have no source for this. But in fact, the Hamburg S-Bahn (Suburban Train) runs with 1200V DC. Rabauz 01:05, 26 Sep 2004 (UTC)

I don't think there's any rule written in stone which dictates the maximum voltage for third rail power distribution, but it would seem that 1500V is a sensible upper limit. There are probably other factors to consider - Is the rail shrouded at all? (bottom-contact systems have less to worry about) How far is the live rail from other rails or the ground? And so on. The more basic systems (the British top-contact 750V third rail is just a bare metal rail sitting on insulators, for instance) could probably be considered to have lower limits for what could be considered a "safe" voltage. -- Mpk 08:46, 28 Sep 2004 (UTC)

In reference to maximum voltage, I believe that leakage at the insulators tends to set the maximum voltage used. Remember, the third rail is sitting in a wet, possibly dirty and salty environment; not the best environment in which to try to provide good electrical insulation!

Atlant 18:57, 17 Dec 2004 (UTC)

[edit] "Electric rope"?

In reference to the Milan underground, is "electric rope" what we usually call "catenary" in english? That is, an overhead wire contacted by a trolley pole or pantograph? If so, can we edit it to say this? Atlant 18:57, 17 Dec 2004 (UTC)

[edit] Milano Line A?

The article referred to the "line A of Milan's underground". There is no such thing as an "A" line in Milan -- there are M1 (red line), M2 (green line) and M3 (yellow line). So I changed the sentence to mention M1 instead of A. I suppose that's correct unless the original writer wrote "A" for some specific reason. LjL 20:51, 30 Mar 2005 (UTC)

[edit] Advantages/Disadvantages

From reading the article I get the impression that third rail is "better" than overhead wire, and that the main reason for using 3rd rail is because its cheaper. However in the 1990s on the Oslo T-bane, two lines, Sognsvannsbanen and Røabanen were converted from overhead wire in the, to third rail. Do you think this was simply to make those lines compatible with the third rail only type stock which the subway company had plenty of, or are there some other advantages with third rail which should be mentioned in the article? Sjakkalle (Check!) 08:37, 9 September 2005 (UTC)

[edit] Singapore has banned what?

"Singapore, for example, has banned their use outside tunnels." Has banned what? Third rail, or overhead line?

[edit] Invention

I notice there have been various bits of tinkering with the "Invention" section, which now claims that Granville Woods invented it in 1901. This is patently absurd, as third rails had been in use on the London Underground for some time by then (the City & South London Railway was powered by third rail at its opening in 1890, and the Waterloo & City opened with third rail a few years later). It's kind of surreally POVish to claim that such things exist only to "disparage his achievement" when it happened ten years earlier, so I'm restoring the original paragraph with a couple of tweaks to make his involvement clear. Woods certainly deserves mention and recognition for the improvements he made, but to claim that he was the original inventor of the third rail system itself is absurd. (And yes, I did actually look up the patent to check. I suggest that anyone else wishing to improve on that paragraph should do so as well.) --Mpk 16:32, 24 December 2005 (UTC)

Likewise, third rail was used in early (pre-1901) electrification of elevated lines in Brooklyn, New York. -- Cecropia 17:13, 24 December 2005 (UTC)

[edit] List of cities

Why does the article open with a long, yet incomplete, list of cities that use third rail systems for their metros and railways? List of current systems for electric rail traction contains a nice comprehensive overview of which system is used where. IMHO this list had better be replaced with something like "Third rail electrification is a common system for metros and subways or for similar light mass-transit railways." --Netvor » user | talk | mail | work » 15:28, 6 January 2006 (UTC)

Well, this is Wikipedia, so you know what to do: be bold! Make the changes you see fit. (I'd suggest leaving the list in this article, but moving it down under its own subhead. IMNSHO, List of current systems for electric rail traction is a pretty messy article.)

Atlant 16:59, 6 January 2006 (UTC)

[edit] 3rd rail lubrication

Does anyone know what the black coloured liquid is that is used to lubricate the rail and the pick-up shoe?--Screen42 11:18, 14 September 2006 (UTC)

[edit] POV or NPOV

Is this POV or NPOV

Visual appeal Third-rail systems cause less visual intrusion: they do not need overhead lines, which some people perceive as unsightly. Singapore, for example, has banned overhead lines outside tunnels. Urban street railways have been built, for example in Washington DC, London, and Brussels, that carry the conductor rail within a slotted box in the center of the track (conduit current collection), primarily to avoid unsightly overhead wires and poles. These resemble the cable slot for a street cable car as seen in San Francisco. Rather than a mechanical grip, an insulated electrical pickup extends into the slot.

Retrieved from "http://en.wikipedia.org../../../t/h/i/Talk%7EThird_rail_6286.html"

Categories: B-Class rail transport articles | Unknown-importance rail transport articles