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Topic Title: Third Rail Always Live?
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Created On: 01 April 2008 01:52 PM
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 01 April 2008 01:52 PM
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mstaple

Posts: 324
Joined: 23 July 2004

Is the third rail on railway lines in the south east always live?

Cheers
 02 April 2008 09:33 AM
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gkenyon

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Originally posted by: mstaple

Is the third rail on railway lines in the south east always live?
I believe so - unless it's been isolated for some maintenance or other activity on or near the permanent way.

-------------------------
Eur Ing Graham Kenyon CEng MIET TechIOSH
 02 April 2008 03:44 PM
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DarrenJF1970

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Joined: 07 March 2007

Yes the 3rd rail is always live 750 volts unless isolated, as stated previously,
 02 April 2008 04:30 PM
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mstaple

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Cheers guys
 02 April 2008 08:40 PM
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AlanKay

Posts: 232
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I always believed that for safety reasons the third rail section in a station was isolated and only switched live when a train approached. At my local station I remember always hearing a mechanical 'clang' about 30 seconds before a train came through.

- My memory could be compromised by a combination of old age and mis-spent youth though...

-------------------------
Alan Kay, CEng MIEE
 03 April 2008 07:40 AM
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DarrenJF1970

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The general public assume that and so more kids who have the impression it is only live when train approaches

The third rail is always live throughout the whole 3rd rail network, unless
isolation has been taken for maintenance work,
isolation been taken through the ECO (electrical controlling officer) who will do this if emergency services need to go on track (same for overhead),
Train driver removes the shorting bar from cab door or emergency cupboard which will short out that section of the 3rd rail network tripping the circuit breaker in sub station

It is possible to stand on the 3rd rail although with all electric, dont touch ground, unless have proper protective gear
 23 January 2009 01:59 PM
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eswnl

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Are we the only country in the world to use 3rd rail on the normal railway?
 26 January 2009 04:22 PM
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amillar

Posts: 1918
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Originally posted by: eswnl

Are we the only country in the world to use 3rd rail on the normal railway?


See http://en.wikipedia.org/wiki/L...stems_using_third_rail

I was surprised how much there is!

-------------------------
Andy Millar CEng MIET CMgr MCMI

http://www.linkedin.com/in/millarandy

"The aim of argument, or of discussion, should not be victory, but progress." Joseph Joubert
 27 January 2009 01:42 AM
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eswnl

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I have also noticed in some areas, especially at stations, the 3rd rail is surrounded by wooden boards. Is it correct that this is not for safety but to stop people using the short circuiting bar between the live and running rails.
 27 January 2009 04:43 AM
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DarrenJF1970

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The reason for wooden boards as you call them are actually better known as kick boards, they are raised higher than 3rd rail and they are there to help prevent people putting / kicking their foot on the 3rd rail. You will find these kick boards, at stations, and at level crossings, and on depots.

The short circuiting bar is there when it is necessary to cut the power on the track, when the train is prepped for the driver, these are checked to ensure they are in place and fit for use if need be.

People that have used these will know it is not something you do unless you really have to, I am not aware of circuiting bar being used in the south east network.
 27 January 2009 12:09 PM
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amillar

Posts: 1918
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Originally posted by: eswnl

I have also noticed in some areas, especially at stations, the 3rd rail is surrounded by wooden boards. Is it correct that this is not for safety but to stop people using the short circuiting bar between the live and running rails.


The NR Personal Track Safety Handbook always used to say "whenever you can, cross the line at a gap in the conductor rail or where protective boarding is provided". (Can't find it in the latest, super-slim, edition.)

-------------------------
Andy Millar CEng MIET CMgr MCMI

http://www.linkedin.com/in/millarandy

"The aim of argument, or of discussion, should not be victory, but progress." Joseph Joubert
 27 January 2009 01:38 PM
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eswnl

Posts: 144
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Originally posted by: DarrenJF1970

The reason for wooden boards as you call them are actually better known as kick boards, they are raised higher than 3rd rail and they are there to help prevent people putting / kicking their foot on the 3rd rail. You will find these kick boards, at stations, and at level crossings, and on depots.



The short circuiting bar is there when it is necessary to cut the power on the track, when the train is prepped for the driver, these are checked to ensure they are in place and fit for use if need be.



People that have used these will know it is not something you do unless you really have to, I am not aware of circuiting bar being used in the south east network.


Does the short circuiting bar get REALLY hot if you put it between the 3rd rail and running rail?

Edited: 27 January 2009 at 01:42 PM by eswnl
 27 January 2009 03:47 PM
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amillar

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From Ellis' British Railway Encyclopdeia: "To prevent the user suffering severe burns a wooden paddle is used to drop it [the short circuiting bar] onto the running rail". Quite!

The breaker for the 3rd rail trips in a matter of milliseconds, but it still makes a big bang on the track. (Not that I've ever seen a shorting bar actually used, but I have some lovely footage of a scaffold pole inadvertently having the same effect!)

-------------------------
Andy Millar CEng MIET CMgr MCMI

http://www.linkedin.com/in/millarandy

"The aim of argument, or of discussion, should not be victory, but progress." Joseph Joubert

Edited: 27 January 2009 at 03:56 PM by amillar
 27 January 2009 07:33 PM
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FerrazShawmut

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Originally posted by: eswnl

Are we the only country in the world to use 3rd rail on the normal railway?


In Bordeaux, the third rail
for ground power supply is between
the tracks and energized only
beneath the length of the tram set
then fully safe for people.
 28 January 2009 02:13 AM
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DarrenJF1970

Posts: 8
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The short circuiting bar does not get hot but like the shorting clips they should be replaced after they have been used.

The correct procedure for using a short circuiting bar is to place it under the running rail, with your back turned to the live rail push the shorting bar down on to the 3rd rail, there will be a loud bang, but repeat the procedure again twice.

The 3rd rail power should be dead, but as we all know, with electricity, treat as live until proofed that its dead.
 28 January 2009 10:52 AM
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broadgage

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Yes, as others post, the conductor rail is allways live unles it has been isolated for some reason, or if the supply has failed.

Even railway staff, who should know better, dont allways believe this to be the case.

It is in theory quite safe to stand on the live rail, since there is no return path for current.
In practice it would be FOOLHARDY IN THE EXTREME to do this since the slightest trip, fall or stumble could result in one foot on the conductor rail and the other foot on the ground, this would probably be fatal.

Many years ago, the nominal voltage was 660 volts, but it is now a nominal 750 volts, except on routes used by channel tunnel trains, where it is 850 volts nominal.
The actual voltage varies substantialy according to load and distance from substation.

The short circuiting bar, carried on all DC electric trains, is indeed used to isolate the supply in case of emergency. And yes it does make a loud bang ! the bar is also used if the current has been cut off, to avoid any inadvertant restoration.

These should not be confused with the track circuit operating clips, carried on all trains, not just electric ones.
These consist of two spring loaded clips connected together by a length of wire. They are intended to be clipped to the 2 running rails, and great care must be taken to not attach them to a live rail.
The puropose of this is to "fool" the signaling equipment into believing that a train is present on an empty track.
This turns the signal(s) to danger and stops other trains.
The purpose is to avoid a train running into wreckage, or persons, following an accident or obstruction on the line.
 28 January 2009 01:44 PM
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Paul1966

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Joined: 21 December 2004

London Underground has a slightly less drastic method for shutting off traction current within tunnels, in the form of two bare low-voltage signaling wires running along the walls which can be pinched together to open the breaker for the section. The trains still carry shorting bars, which can be clamped between positive and negative conductor rails to prevent re-energizing of the track, e.g. if passengers have to be walked out of the cab to the next station.

In Bordeaux, the third rail for ground power supply is between the tracks and energized only beneath the length of the tram set then fully safe for people.


What method is used to detect presence and energize only the sections required?

Edited: 28 January 2009 at 01:45 PM by Paul1966
 28 January 2009 07:30 PM
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eswnl

Posts: 144
Joined: 29 November 2008

Would anyone be kind enough to post a picture of this short circuiting bar?
 28 January 2009 09:47 PM
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DarrenJF1970

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If you send me your email address I will send you a photo later on during the night, my email is DarrenJFerguson1970@yahoo.co.uk
 30 January 2009 11:29 AM
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z315870

Posts: 65
Joined: 30 May 2003

A quick point - when using track circuit operating clips in a third-rail area, the safe procedure is to clip onto the rail FURTHEST from the third rail first. The clips are designed so that if you do this, you then can't accidentally reach the third rail and short it by mistake (which would probably make the cable explode in your face).

-------------------------
Dr Joe Silmon PhD MEng CEng MIET
Committee Member, Railway TPN
IET » Transport engineering » Third Rail Always Live?

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