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Trog
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What's with that 4th rail?

Is it just retained for bonding/earth purposes as it is not on pots (and with now being lower, doesn't need an end ramp)?

Presumably where LU stock used to go but now sees only 3rd-rail stock.

Edited by keefer
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4 hours ago, keefer said:

What's with that 4th rail?

Is it just retained for bonding/earth purposes as it is not on pots (and with now being lower, doesn't need an end ramp)?

Presumably where LU stock used to go but now sees only 3rd-rail stock.

Yes.

 

Earthing on dual-electrified sections is a black art.  I suspect when the fourth rail was no longer needed someone thought it was easier to just keep it instead of risking problems with stray current, which has been known to corrode the bases of OLE masts to the extent they needed replacing.  

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It wasn’t so much a stray current problem as high resistance in the return circuit, leading to problems achieving workable and safe circuit breaker settings, that led to the retention of the fourth rail. The LM region got into a few tangles about managing return circuits and breaker settings on the Watford dc lines at around the time this was done, and had to enlist help from the southern.

 

There are similar sections of ‘negative reinforcing’ at odd places on the southern, typically where lines have been singled, reducing the number of parallel running rails in the return circuit - Newhaven to Seaford was one, and I presume still is.

 

The sign doesn’t look like a coasting board, which were usually white diamonds, and my guess is that it banned use of the semi-permissive capability of the old signalling in ‘darkness, fog and falling snow’ due to poor sight-lines, but that is only a wild guess.

 

 

Edited by Nearholmer
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8 hours ago, Nearholmer said:

The sign doesn’t look like a coasting board, which were usually white diamonds, and my guess is that it banned use of the semi-permissive capability of the old signalling in ‘darkness, fog and falling snow’ due to poor sight-lines, but that is only a wild guess.

 

 

According to the railsigns website it is a coasting board, a design particular to the Watford line. See fig. 25.21 on this page of the site: https://www.railsigns.uk/sect25page2/sect25page2.html

Edited by hexagon789
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14 hours ago, Nearholmer said:

The sign doesn’t look like a coasting board, which were usually white diamonds, and my guess is that it banned use of the semi-permissive capability of the old signalling in ‘darkness, fog and falling snow’ due to poor sight-lines, but that is only a wild guess.

The white diamond coasting board is essentially a feature of the Southern. The LMS/BR(M) often did things differently on their DC railways.

 

14 hours ago, Nearholmer said:

It wasn’t so much a stray current problem as high resistance in the return circuit, leading to problems achieving workable and safe circuit breaker settings, that led to the retention of the fourth rail. The LM region got into a few tangles about managing return circuits and breaker settings on the Watford dc lines at around the time this was done, and had to enlist help from the southern.

 

There are similar sections of ‘negative reinforcing’ at odd places on the southern, typically where lines have been singled, reducing the number of parallel running rails in the return circuit - Newhaven to Seaford was one, and I presume still is.

Essentially correct. Much of the Watford DC Line is single rail track circuited as a consequence of its past 4-rail electrification. With conversion to 3-rail in the 1970s, having only one running rail for traction return is not sufficient in terms of providing a sufficiently low resistance return path for traction current, so the original 4th rail is retained over significant stretches simply to act as a parallel conductor, bonded to the traction return rail. For the section from Kilburn High Road to Harrow & Wealdstone the 4th rail, bonded to the traction return rail, is still in use for London Underground's benefit.

 

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59 minutes ago, jim.snowdon said:

 

Essentially correct. Much of the Watford DC Line is single rail track circuited as a consequence of its past 4-rail electrification.

 

 

 

[Pendant mode on - and not a dig at you Jim]

 

Thats Single Rail Traction Return!

 

There is no such thing as a 'Single Rail Track Circuit*' as ANY track circuit requires to pass through both running rails to function.

 

* However you do hear the phrase used by S&T as shorthand for "50HZ AC Track Circuit with Single Rail Traction Return" to differentiate it from the "50HZ AC Track Circuit with Double Rail Traction Return" configuration as they are wired up differently and involve different / extra components, the later most notably requiring 'Impedance bonds' (or 'spiders' for non SR / p-way types) in the 4ft which are obviously rather impractical in 4th rail areas).

Edited by phil-b259
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It was always called ‘SRTC’ though.

 

I did absolutely thousands of DC breaker setting calculations in the late 70s and early 80s, including the Watford line ones, and even the reference diagrams that we used were marked ‘SRTC’, with the ‘TC’ being pronounced ‘track circuit’. Everyone knew that wasn’t to be taken literally, but that was what it was called.

 

 

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3 hours ago, Nearholmer said:

It was always called ‘SRTC’ though.

 

I did absolutely thousands of DC breaker setting calculations in the late 70s and early 80s, including the Watford line ones, and even the reference diagrams that we used were marked ‘SRTC’, with the ‘TC’ being pronounced ‘track circuit’. Everyone knew that wasn’t to be taken literally, but that was what it was called.

 

 


Down our way the S&T nomenclature used is ACDR or ACSR [edit] (the 50Hz type that is)

 

Not sure how the ETE department refer to them though

 

 

 

Edited by phil-b259
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2 hours ago, phil-b259 said:


Down our way the S&T nomenclature used is ACDR or ACSR.

 

Not sure how the ETE department refer to them though

 

 

 

This end of the ETE department knows them as Single and Double Rail, I suppose from the fact that the traction return is either single or double rail, but then the signalling courses I have been have also referred to them as single or double rail. I've always looked on that being either IRJs on both rails (double rail) or in just one rail, ignoring the transpositions required in S&C.

 

Interestingly, the term 'spider plate, is used only north of the Thames, where it is just a short busbar that serves as a connection point for the multiple negative cables from the track and is mounted in the cess. South of the Thames, the connection plate, whether mounted between impedance bonds or on its own in the four-foot, is an 'advance plate'.

 

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39 minutes ago, jim.snowdon said:

This end of the ETE department knows them as Single and Double Rail, I suppose from the fact that the traction return is either single or double rail, but then the signalling courses I have been have also referred to them as single or double rail. I've always looked on that being either IRJs on both rails (double rail) or in just one rail, ignoring the transpositions required in S&C.

 

 

"double railer" "single railer" shorthand terms are also used down my way to describe track circuits configurations - just as we might refer to a TI21 / EBI 400 as a 'low power' or 'normal power'

 

However, as I have said to many an apprentice over the years the shortened term is something which should only be used once the person has appreciated what is really being talked about i.e. the path traction current takes. This is in turn necessary because it has a considerable effect on the track circuit equipment installed plus the readings you get when all is not as it should be.

 

Traction current imbalances in a double rail setup can have a significant effect on S&T readings, while the 'chunkiness' of the bonding used on S&C will depend on whether its only taking S&T currents (and thus our responsibility) or traction current (and thus a ETE responsibility) for to give a couple of examples. Front line S&T faulting and maintenance techs therefore need to always consider whether the traction return is doing what it should during testing.

 

So because RMweb members, (as with some of the apprentices I have dealt with over the years) are unlikely to appreciate the significance of the terms 'single Rail' and 'Double rail' when used in association with track circuits, I feel it is important that the fully descriptive "xx rail traction return" is used.

 

39 minutes ago, jim.snowdon said:

 

Interestingly, the term 'spider plate, is used only north of the Thames, where it is just a short busbar that serves as a connection point for the multiple negative cables from the track and is mounted in the cess. South of the Thames, the connection plate, whether mounted between impedance bonds or on its own in the four-foot, is an 'advance plate'.

 

 

Indeed, I have never heard of it referred to as a 'spider' by Southern region based folk (other than newbies who are pretty quick to start calling it the 'advance plate' like the rest of us. But on the other hand say 'advance plate' to those based 'north of the river' as it were and you usually get bank faces till you chuck in the term 'spider'

 

Yet more evidence that despite all the attempts to standardise or group the railways into one organisation, regionalism or a tribal attachment to the way a particular route does things is still strong...

Edited by phil-b259
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7 hours ago, jim.snowdon said:

The LMS/BR(M) often did things differently on their DC railways.

...................

 

 

The P-Way were still using LNWR/LMS diagrams on how to set up the con rail up until Railtrack came on the scene and mandated BR SR type standards presumably not even knowing that the LNWR ones were still in use on the DC. Although some parts were getting hard to find, for example for some obscure reason no one made pots to fit the LNWR 1914 vintage 105lb conductor rail which had a narrower foot than all the modern sections. So we had a company in Newport Pagnell who did metal bashing for Aston Martin, make us some top packs that included a set of ears that shimmed the gap between the sides of the rail and the ears on the standard pots. Who said that the DC line was not posh.

 

We also had to use London Transport 317P21 pots under the fourth rail as none of the BR standard sizes were short enough. However the LT pots seemed to be a slightly different size to BR ones, so you had to remember not to do the screws holding down the pot ring clips too tightly or the pot would break. Amazing how much know how is needed just to put a bit of elderly steel on a few pots.

 

Impedance bonds were always referred to as spiders by the LMR PW, they were often to be found living between two glued joints just out side tunnels. 

Edited by Trog
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On 03/09/2021 at 08:19, Nearholmer said:

Since JS, and rail signs say it’s a coasting board, then it must be; possibly.

 

Has anyone got an old sectional appendix or local instructions that identify it?

Would you believe that my relevant 1960 Sectional Appendix for some reason has about 25 missing pages - including the pages with the DC Lines Instructions - pah!

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15 hours ago, Trog said:

 

The P-Way were still using LNWR/LMS diagrams on how to set up the con rail up until Railtrack came on the scene and mandated BR SR type standards presumably not even knowing that the LNWR ones were still in use on the DC. Although some parts were getting hard to find, for example for some obscure reason no one made pots to fit the LNWR 1914 vintage 105lb conductor rail which had a narrower foot than all the modern sections. So we had a company in Newport Pagnell who did metal bashing for Aston Martin, make us some top packs that included a set of ears that shimmed the gap between the sides of the rail and the ears on the standard pots. Who said that the DC line was not posh.

 

We also had to use London Transport 317P21 pots under the fourth rail as none of the BR standard sizes were short enough. However the LT pots seemed to be a slightly different size to BR ones, so you had to remember not to do the screws holding down the pot ring clips too tightly or the pot would break. Amazing how much know how is needed just to put a bit of elderly steel on a few pots.

 

Impedance bonds were always referred to as spiders by the LMR PW, they were often to be found living between two glued joints just out side tunnels. 

As far as I know, there's still no one making pots for 105lb conductor rail. In fact, there are remarkably few people who even have copies of the 105lb rail section (I'm one of them), but I wasn't aware of the 'Aston Martin mod' - thanks for that little titbit. It's still fun getting connections to it as none of the modern crimp lugs for the feeder cables will fit. We do have workarounds for that.

 

Interestingly, I haven't heard of the impedance bonds themselves being called spiders by the LNW people (that doesn't say the term isn't in use) but I have come across them being referred to as impedance tanks. The term 'spider plate' seems to be reserved these days for just the connection plates, most of which (as a consequence of single rail traction return) are lineside on LNW. The equivalent in axle counter areas on the Southern is in the four foot, acting as the interface between the stiff 800mm2 negative cables and the flexible side leads used to connect to the rails.

 

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3 hours ago, corneliuslundie said:

I hope all the modellers reading this and modelling DC lines are therefore now using the right components and terminology!

Jonathan

Depending on whether they are modelling the Southern, the Watford DC/North London Lines, the Liverpool area or the Tyneside systems. The last one has been gone for so long that its terminology has been lost forever.

 

 

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On 03/09/2021 at 14:16, phil-b259 said:

 

 

[Pendant mode on - and not a dig at you Jim]

 

Thats Single Rail Traction Return!

 

There is no such thing as a 'Single Rail Track Circuit*' as ANY track circuit requires to pass through both running rails to function.

 

* However you do hear the phrase used by S&T as shorthand for "50HZ AC Track Circuit with Single Rail Traction Return" to differentiate it from the "50HZ AC Track Circuit with Double Rail Traction Return" configuration as they are wired up differently and involve different / extra components, the later most notably requiring 'Impedance bonds' (or 'spiders' for non SR / p-way types) in the 4ft which are obviously rather impractical in 4th rail areas).

 

Surely it is a railway tradition to name things what they are not. Like the way SHC rail clips are often stamped BJB so those new to the P-Way will not confuse them with BJB rail clips.

 

As it is obvious to even the meanest intelligence that having BJB stamped on BJB clips would just be too confusing, as those reading it would spend most of the rest of their shift wondering what the catch was.

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On 04/09/2021 at 11:42, The Stationmaster said:

Would you believe that my relevant 1960 Sectional Appendix for some reason has about 25 missing pages - including the pages with the DC Lines Instructions - pah!

I've checked the various issues of the Sectional Appendix from the time the line was resignalled and can't find anything. 

Has anyone got a copy of BR29636 Working Instructions for D.C. Electrified Lines between Euston - Watford Junction - Croxley Green and Broad Street - Richmond. That may provide a clue.

 

 

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40 minutes ago, TheSignalEngineer said:

I've checked the various issues of the Sectional Appendix from the time the line was resignalled and can't find anything. 

Has anyone got a copy of BR29636 Working Instructions for D.C. Electrified Lines between Euston - Watford Junction - Croxley Green and Broad Street - Richmond. That may provide a clue.

 

 

I have a 1975 edition of said Instructions, and it doesn't say anything about either coasting signs or signs with white crosses thereon.

 

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