Third Rail: Is my plan correct?

[Southernboy]

Hello all,

 

firstly I hope this is the right place to post my query.

 

I'm about to start laying third rail on one section of my layout and would much appreciate advice on whether or not my plan is correct.

 

 

I've read the Russ Elliott webpage, so hope I'm reasonably ok, but would appreciate any knowledgeable feedback.

 

If it helps - my area/era is South London, Southern Railway c. 1920s/1930s.

 

Third rail is in pink, running lines in black.

 

As I understand it (for N gauge) ramps are 14mm approx, overlaps should be 12 sleepers approx, minimum clearance between conductor rails converging at the intersection of points 1.3mm.

 

Whilst on the subject of third rail - I'd be interested to learn more about 'section gaps' and 'switch gaps' (what's the difference / what purpose do they serve?) and 'expansion gaps': For eg for all of the aforementioned - are they at regular intervals (and if so what?) - or do other parameters apply (if so, what are they?) etc.

 

I'd also be interested to know the average distance between power feeds from substations. And were these at regular intervals, or more concentrated the greater the distance from the substation (power drop? or were substations positioned to avoid power drop?) / more concentrated according to traffic demand? ... should there be power feeds on my section of line as shown?

 

If it helps - there will be a substation a short distance at the opposite end of the station shown on my plan.

 

There are so many things about third rail I don't understand - so please throw everything you have at me

 

With thanks in anticipation,

 

Mark

 

 

 

[Gwiwer]

My immediate comment is that the conductor rail should be in the "six foot" between the up and down main for both those tracks, and also on the opposite side of your reversible line. Conductor rails on the "outside" were frowned upon because of the need for staff to walk along the trackside and for drivers (motormen in SR parlance) and occasionally others to have to step down from the train on this side.

 

I am not in aposition to give detailed comment on the technicalties of the third rail system from that era but in general there is a considerable potential for current drop with DC systems requiring more frequent inputs and "paralleling" (hence Track Paralleling Hut) or evening out of current between up and down tracks.

 

Section gaps are required to electrically isolate sections just as we do when powering our models. Otherwise with the whole thing live any given section could not be isolated in emergency without bringing the entire network to a grinding halt.

[TheSignalEngineer]

My first impression is that there is too much conrail in the area of the points. There will be gaps, as trains have multiple shoes this is not a problem.

[Gwiwer]

Quite correct. The juice rail often reaches points but does not make a continuous run through them. There would be a ramped end instead.

 

It was far from unknown for a short train such as a 2-car unit to become "gapped" if travelling so slowly that all shoes left the juice rail simultaneously. On the Frankland Park diagram above this could occur during movements to and from the "Relief" platform and Up Main or Reversible lines.

[Oldddudders]

Would one of our signalling experts like to comment on a bi-di line in the pre-war period? Easy-peasy now, perhaps less so then?

[beast66606]

Would one of our signalling experts like to comment on a bi-di line in the pre-war period? Easy-peasy now, perhaps less so then?

 

Easy enough to do but unlikely, unless it was a branch line (imho)

[10800]

My immediate comment is that the conductor rail should be in the "six foot" between the up and down main for both those tracks, and also on the opposite side of your reversible line. Conductor rails on the "outside" were frowned upon because of the need for staff to walk along the trackside and for drivers (motormen in SR parlance) and occasionally others to have to step down from the train on this side.

 

My understanding for plain track, and correct me if I'm wrong, is that 'left hand side in the direction of travel' was the default, unless operational hazards dictated otherwise. Thing is, there are so many hazards that the default is often the minority condition, except maybe out in the country between stations. So your comment probably applies in most urban and station environments.

[Oldddudders]

I think the only reversible electric lines in the '30s - other than those sections within station limits, of course - were Wimbledon - West Croydon, several sections controlled by electric train staff, and Ash Vale - Frimley Junction, controlled by electric tablet. In this era Southern opened two new lines, electric from the opening, but these were both double-track throughout - the Wall of Death from Sutton to Wimbledon in 1930, and the Chessington Branch in 1939 - and used ABS.

[Gwiwer]

I will of course defer to those with greater knowledge of the subject but while I also understand that "left hand side" was at one time the default (though seldom the location for all sorts of reasons!) that by the time of main line electrification in the early 30s, just after the OP timeframe, then "right hand side" had become the default.

[The Stationmaster]

According to my copy of the Southern Railway 1925 'Instructions For the Guidance of Staff on The Electrified Lines (Direct Current Conductor Rail System)' the following applied at that time -

 

'This (conductor) rail is generally laid on the left hand side of the track, but at certain stations, crossover roads, junctions and other places it is laid on the right hand side. Timber guards are provided alongside the conductor rail at certain places'

[TheSignalEngineer]

Would one of our signalling experts like to comment on a bi-di line in the pre-war period? Easy-peasy now, perhaps less so then?

More likely to find a unidirectional slow or goods line I would have thought.

[Southernboy]

Firstly to say thank you to all for your helpful and informative responses. I appreciate your feedback.

 

Rather than reply to each in turn I've summarised what I hope is a reasonably accurate precis of comments in respect of third rail plan:

 

Points mechanisms should be free of third rail.

In this period third rail was initially on the left of the direction of travel, but later was changed to the right hand side. In later years still practice changed to a central position.

For this exercise I'll stick to left, as I guess it took a few years for the rules of the 1920s to be countermanded by those of the 1930s, and I'm modelling midway between the two.

 

How does this plan look?

 

I've introduced an additional element upper right: A fog hut.

Would the third rail be moved to the other side for safety reasons?

And would it have a protection board on the near side?

 

As to 'Relief Line' and 'Bi-Directional line': I plucked those terms arbitrarily from the sky when I was first planning the layout (they just made sense to me at the time), so perhaps I should now explain further ...

 

The 'Relief Line' (left) is for express up traffic in the morning rush hour and down traffic in the evening to overtake slow or semi-fast trains. I distinctly remember reading about particularly strict rules/practices/signal box interlocking being introduced around the London Bridge area for such traffic flows, although annoyingly I now can't remember in exactly which edition of which publication it was published.

 

As to the 'Bi-Directional Line (right)': this flows to carriage sidings and two bay platforms, which similar to above, would generally see traffic moving in one direction in the morning, and in the opposite direction in the evening, with few, or no movements midday.

 

If I'm wrong and lines over which trains trains could travel in both directions did not exist - than I need to work out how the Southern Railway in their mindset of the time would have handled such operations.

 

So ok - back to the experts - is my third rail plan any better now?

 

Thanks again,

 

Mark

[Gwiwer]

In later years still practice changed to a central position.

 

Southern third rails were never in a "central" position if that means between the two running rails. Your statement that

In this period third rail was initially on the left of the direction of travel, but later was changed to the right hand side.

is adequate on its own.

 

There were many exceptions to any rule based upon local operational needs and circumstances. Anywhere that staff might be required to frequently come into close proximity of the track the third rail would be placed on the opposite side if at all possible to minimise risk or - if the distance were short - there may simply be a gap in the "juice". So passing your fog hut there might be a short gap without the added complication of the conductor rail changing sides for just a few yards.

 

Your platform working seems admirable in that a train calling at a station instantly reduces line capacity by occupying the same stretch of track for longer than it would if it kept moving. SR station stops were allowed 20 seconds except where the working timetable specifically provided for longer such as half-minute or even minute long stops. Allowing a closely-following train to draw up in an adjacent platform or even run through (overtake) then mitigates much of this effect allowing maximum track capacity during peak times.

 

The "bi-directional line" works for up morning peak trains but not for the evening down ones - those would have to cross the up line twice (once at the "London" end and again approaching your station) which causes loss of capacity by blocking up trains for perhaps a couple of minutes at each crossover every time. The SR had few such sections of line and it might be worth considering the way other places do such things.

 

Melbourne (Australia) has a fair number of triple track sections some of which are quite lengthy and include many intermediate stations. The central track is the reversible one and used in the up direction for morning peaks and down for evening peaks. In most cases the central track is actually used as the full-time down track with the outer (down) track being used for the entire morning peak and evening peak overspill services. No conflicting moves are introduced operating in this way.

[beast66606]

As to 'Relief Line' and 'Bi-Directional line': I plucked those terms arbitrarily from the sky when I was first planning the layout (they just made sense to me at the time), so perhaps I should now explain further ...

 

The 'Relief Line' (left) is for express up traffic in the morning rush hour and down traffic in the evening to overtake slow or semi-fast trains. I distinctly remember reading about particularly strict rules/practices/signal box interlocking being introduced around the London Bridge area for such traffic flows, although annoyingly I now can't remember in exactly which edition of which publication it was published.

 

As to the 'Bi-Directional Line (right)': this flows to carriage sidings and two bay platforms, which similar to above, would generally see traffic moving in one direction in the morning, and in the opposite direction in the evening, with few, or no movements midday.

 

If I'm wrong and lines over which trains trains could travel in both directions did not exist - than I need to work out how the Southern Railway in their mindset of the time would have handled such operations.

 

 

I stand by my original statement, unlikely but happy to be shown the prototype - remember London Bridge was a tad bigger and busier than your station, what applies (assuming it did) at a major through station with umpteen platforms and multiple branches does not necessarily make sense at a small "country" station with a couple of running lines.

 

I have some signal box diagrams for London Bridge but these are the pre-colour light ones so probably not relevant. It's not difficult to do, but its potentially very dangerous if something goes wrong, platform lines were frequently bi-directional, where speeds would be low but stretches of running line - I remain to be convinced (for the era you are modelling)

[Oldddudders]

The 'Relief Line' (left) is for express up traffic in the morning rush hour and down traffic in the evening to overtake slow or semi-fast trains. I distinctly remember reading about particularly strict rules/practices/signal box interlocking being introduced around the London Bridge area for such traffic flows, although annoyingly I now can't remember in exactly which edition of which publication it was published.

I think this is my point about the time-frame for your lovely layout being a little premature for bi-di running. The line you recall from the article is 2 Reversible, which came into use in that guise in April 1976, when the new London Bridge box was commissioned for traffic on the Tuesday after Easter. From that date, the lines between North Kent East Junction and London Bridge were as follows, number 1 line being closest to the Thames :

 

1 Down

2 Reversible

3 Up

4 Down

5 Down

6 Up

Up Passenger Loop

 

The RVL was used - maybe still is - just as you suggest, with Up Cannon Street trains using it in the morning, Down CSt trains in the evening. Modern means of controlling signalling interlockings meant that all the access to and from the RVL were/are contained within the control of London Bridge. On the Thursday preceding the Easter weekend, North Kent East Junction signalbox signalled the last Up Bexleyheath line train of the day - and once the driving cab had passed, a man put an axe through the cables to his last Up controlled signal! NKE Junction box was abolished over the next few hours. By the Sunday morning, when I took duty as Traffic Regulator in the new box, 8-EPB test trains were testing routes all over the new layout. 2 Reversible has a series of "direction of flow" indicators on the signalling panels concerned (I think it's/it was Panels 3 & 4) and of course the electronics just take over once the signaller has stripped the route up. Prior to that Thursday, the line was not reversible, and the layout was completely different, with a major bottleneck at Borough Market Junction, immediately on the CX/CSt side of London Bridge.

 

The only location I can think of where a reversible line existed between signalboxes was between East and South Croydon boxes. Although these were commissioned in 1955 (?), I'm not sure that the line became reversible until a few years later. Irritatingly, I spent an evening pulling the down side levers in East Croydon box in early 1968 (under close supervision!), but can't recall how the RVL signalling worked to ensure "direction of flow" between the two boxes. I may be able to find out.

[SwissRailPassion]

When planning the track the railway engineers on a through route would want to consider the service pattern and to keep things moving most efficiently. The up and down traffic is to be kept moving and clear of each other. This would be best done by providing pairs of fast and slow lines. Bi-directional running is a relatively modern practice as mentioned by the other posters. 2 track and 4 track are the most common on SR. Why not add a down slow and make the bi-di the more prototypical up slow? Also I believe conductor rails should be kept away from platorms and placed in the six-foot.

[DonB]

the OP does not say whether the 3rd rail is live or cosmetic. If live how do models "coast" over the gap?

[Oldddudders]

Here is a quote from the excellent Westinghouse site http://www.wbsframe.mste.co.uk/public/East_Croydon.html

 

"Reversible Line

From the 1st June 1958, the down relief line. between Windmill Bridge junction at Gloucester Road and South Croydon was signalled as 'Reversible' line, any down train could travel over the line as before. However Up direction Oxted line trains only could now run in the UP direction. This was done to reduce the number of Up direction train movements onto the up main line, which in effect cut the two main line tracks for the duration of the movement. East Croydon had overall control of the Reversible line and its signals, East Croydon releasing the signals at both Gloucester Road Junction and South Croydon. Trains could also enter or leave the Reversible line at East Croydon if so desired."

 

What this tells us is that as late as 1958, control of "wrong" direction moves onto a bi-di line would need to be controlled from one box, and this might have been tougher to do in the era of Frankland. Note that this is a completely different scenario from conventional single-line operation, where a staff, tablet or other piece of hardware would typically be provided for the driver to have in his possession before entering the single line. We are here talking about Track Circuit Block operation with colour light signals, where block instruments and bells are not used in the normal course of operation (although bells exist for emergency use).

[beast66606]

When planning the track the railway engineers on a through route would want to consider the service pattern and to keep things moving most efficiently. The up and down traffic is to be kept moving and clear of each other. This would be best done by providing pairs of fast and slow lines. Bi-directional running is a relatively modern practice as mentioned by the other posters. 2 track and 4 track are the most common on SR. Why not add a down slow and make the bi-di the more prototypical up slow? Also I believe conductor rails should be kept away from platorms and placed in the six-foot.

 

I think it's highly unlikely that 4 tracks would be provided just to keep the up and down separate, that happens on double track too

Bi-directional running is not new, it's alternate name is "single line working" and on double (or more) tracks plenty of larger stations had it, but running it over long lengths of railway in a tidal manner, is.

 

[TheSignalEngineer]

the OP does not say whether the 3rd rail is live or cosmetic. If live how do models "coast" over the gap?

If live, as in the prototype there will need to be multiple shoe beams. Conductor rail should be designed to eliminate instances of a train losing contact with the power supply if possible.

[TheSignalEngineer]

I don't know if this has been posted before, but this page has a lot of information about both 3rd and 4th rail electric arrangements http://homepage.ntlworld.com/russelliott/3rd-4th.html

[Southernboy]

Thanks again gentlemen for your considered, detailed and informed replies, I am indebted to you.

 

 

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For the third rail then I have noted:

 

I need breaks to third rail 'both' sides of the points, not one.

Breaks in third rail in areas of frequent staff movement.

 

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In answer to the query: My third rail is cosmetic. Whilst I do like detail, live third rail is a challenge too far for me.

 

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Now to my 'relief line' and 'bi-directional line'.

 

Well I'm disappointed to learn such lines did not exist then (the more you learn, the more you realise there is more to learn still).

 

As you've all taken the trouble to give me such detailed feedback - I feel a detailed explanation is warranted.

 

Firstly please take a minute to check this short YouTube clip:

http://www.youtube.com/watch?v=R4ZFi3Pcyy4

 

It was an inspiration and 'scene setter' for me when designing my layout.

But I only have 1m x 2m of modelling space. So how to represent what I had in my mind's eye?

 

Vis:

 

The eight or so approach lines to Waterloo running on a viaduct.

The multiple sidings between main lines at Clapham,

The five lines running through sunny, tree-lined Surbiton.

The six or more lines running through the respectable suburb of Wimbledon.

 

Clearly serious distillation into 'essence of' was required.

 

One thing it certainly could not be was a simple 'two track roundy' ... that would have no chance of capturing the spirit of what I wanted. So the exercise became one of creating the illusion of multiple trains running in close succession over numerous lines in two directions - even though in reality it couldn't be. So I had to come up with best 'visual impression' of what I envisaged given the limited space I had.

 

I like to think that I didn't do too bad a job for someone who only started modelling four years ago (there's a lot to learn!)

 

 

 

Ultimately for most of us it becomes an academic exercise as to the best compromise we can come up with which best represents what we'd love to model, within the space confines we have ...

 

 

So there you have it, I hope my thought process / layout design makes sense.

 

Just please don't go telling anyone else that my bi-directional lines didn't exist then, because you'll just completely spoil the illusion that I'm trying to create

 

Thanks again,

 

Mark

[10800]

I don't know if this has been posted before, but this page has a lot of information about both 3rd and 4th rail electric arrangements http://homepage.ntlw...tt/3rd-4th.html

 

This is the item referred to in line 4 of the OP I believe.

[Southernboy]

Here's the most recent revision:

 

 

I think there will be a barrow crossing at the end of the platforms, so more revisions there ... but in general hopefully this fits the consensus?

[SwissRailPassion]

Lovely drawing of the entire layout, I can see what you're aiming for. My point about 4 tracking was that it was carried out when the up and down lines were insufficient due to a mixture of express and stopping trains. From 2 to 4 rather than 3. When it comes to a layout, however, compromise is everthing, and in the size available, the art of creating the essence of the railway comes first when size is at a premium. Yours will certainly look busy and the loop platform will provide added interest.

 

A layout is a stage, a little theatre, where the entrance of the characters (trains) is significant and the depth of field has to be foreshortened and scales have to be carefully considered to make he whole thing much deeper and bigger than it really is. Less is often more.