Advice needed on cable troughing and relay box positions

[TheSignalEngineer]

On 17/05/2020 at 22:53, St. Simon said:

 

There isn’t any real design standard on locating Location Cases*

* Bearing in mind I’m a schemes guy, I haven’t come across a standard just yet!

There was one but like so many other things the Railtrack T***s with no railway knowledge brought in from other places by the government to show us how to do things better at the time of privvytisation threw it away.

 

(Political Rant Over)

[Trog]

26 minutes ago, TheSignalEngineer said:

There was one but like so many other things the Railtrack T***s with no railway knowledge brought in from other places by the government to show us how to do things better at the time of privvytisation threw it away.

 

(Political Rant Over)

 

Yes it was very annoying being told how to relay track by people who had only ever done it using components supplied by Hornby, and who would not have been able to recognise an F19 sleeper if you inserted it where the sun does not shine.

[phil-b259]

On 20/05/2020 at 21:40, Powerhaul 70 Pey said:

Good evening to everyone and thanks for the help and information following my initial question.

 

I have searched TWPS loops on this forum but not found too much info.  I have read that they are positioned 180m from a signal.  I have searched through my photos and found 2 examples below.

 

Location is Euxton with this particular TWPS on the fast line to which Euxton junction is literally around the curve in the distance.  Would there be another at the next signal?

 

Warrington Bank Quay with one in the middle of platform.  Would there be another at the next signal?

 

I am just curious as to their positioning relative to any signals, stations and junctions.

 

 

 

Right, first the basics.

 

 

• TPWS is designed to prevent train collisions. It is NOT designed to prevent signals from being passed at danger!
• TPWS is fully compatible with mechanical signalling and there is no difference in how it is applied to the tracks.
• TPWS can be associated with signals AND to enforce enforce permanent speed restrictions.
• TPWS installations (note the 's') consists of an 'arming' loop which starts a timer on the traction unit and a 'trigger' loop. You cannot have a single stand alone loop for TPWS to work!
• The term 'grid' comes from the Fibreglass structural part - the loop itself is literally a loop of wire round the edge that forms a radio transmitter
• Each loop transmits a precise and specific (different for each type of loop) radio frequency which is picked up by an aerial under the train
• There is a timer on the traction unit FIXED at 1 second for passenger trains and slightly longer for freight*.
• If the traction unit passes over the 'trigger' loop before the timer has timed out then the emergency brakes come on and will not release until the traction unit has been stationary for 2 minutes.
• If the brakes are applied by the TPWS then the traction unit is said to have been 'tripped' by the TPWS

 

Now TPWS as applied to the track.

 

TPWS at any given location will usually consist of TWO, or sometimes three separate installations which work together to provide TPWS.

 

(1) A Train Stop installation (TSS)

 

• The 'arming' and 'trigger' loops are laid back to back in line with the signal. The layout of these loops will ensure that even a loco moving a walking pace will get a TPWS activation if it passes the signal at Red - as the FIXED timer on board the train (started by the arming loop) will not have finished timing out before the train aerial receives the frequency from the 'trigger loop'

 

• However on its own a trainstop installation will not prevent a collision if the train is travelling at any sort of speed (given how long it takes for trains to stop) when it gets tripped - and that brings us to the second component.....

 

(2) A Over Speed installation (OSS)

 

• This is designed to catch drivers who have NOT reacted to cautionary signalling aspects leading up to the red signal and who will be approaching a red signal at such a speed that the TSS will not be able to stop them before they come into conflict with another train.

 

• The OSS thus works on the principle of:- "Well the driver is coming up to a red signal, so at ZZ meters / yards back from the signal they should have reduced their speed to no more than XX mph"

 

• ....So...

 

• "IF the driver is travelling below XX mph then no intervention is required, but IF they are travelling above XX mph then we need to activate the emergency brake and stop them"

 

• Fortunately it is easy to do this with TPWS by adjusting the spacing of the 'Arming' and 'Trigger' loops. The further apart they are the faster a train can go without passing over the 'trigger' loop within 1* second of passing over the 'arming' loop.

 

• The 'trip' speed is carefully selected based on the braking curves that apply to that particular line for passenger trains (differences in braking characteristics between train types less of an issue due to the adoption of different length timers on EMUs / DMUs / locos undertaking passenger work and freight locos). The trip speed also must factor in the maximum line speeds allowed plus the ruling gradients that a train will encounter as it goes from green through the cautionary aspects to red as the laws of physics means its harder to slow a 60mph train going downhill than it is a 60mph train going uphill.

 

• Thus an OSS installation on a line where the 'trip speed' is 30mph will see the two OSS loops closer together, and closer overall to the signal to which they apply than a line which has a 50mph trip speed.

 

• It is thus important to note that the placement of OSS loops is thus bespoke to each site, determined by a complex set of calculations and NOT A SET DISTANCE! Modellers need to pay attention to this and appreciate you won't find any form of 'standard placing' to use.

 

• But to return to the real railway, the problem with an OSS is that at very high speeds (100+mph) the loops end up being so far back and so widely spaced that they won't provide protection for slower trains - who might be well under the 'set speed' / 'trigger speed' but would still not be stopped by the TSS installation at the red signal before coming into conflict with another train. Thus an OSS has limits on how far back from the signal to which it applies it can be sited - and the limits chosen means it can only stop a train from coming into contact with another train if the train you want to stop is doing 75mph or less. Please note this does not mean all OSS installations are set for 75mph - most will be considerably lower, but 75mph is the absolute maximum for it to still be effective at doing the job it is designed to do.

 

(3) Over Speed Plus (OSS Plus)

 

• This will be fitted where the line speed is grater than 75mph - and in addition to the TSS and OSS installations described above. Again it uses 'arming' and 'Trigger' loops spaced a certain distance apart to trigger a FIXED timer on the train and activate the emergency brakes if it passes over the 'Trigger' loop within 1* second of being activated by the 'Arming loop'

 

• As with the ordinary OSS, the OSS Plus installation is based on the fact that drivers should be reducing their speed in line with the cautionary signal aspects and be preparing to stop - if they haven't then TPWS makes sure they do!

 

• Frequently the position of OSS plus loops end up being so far in rear of the signal they relate to that they actually end up encroaching into the previous signal section. There have been more than a few occurrences over the years of drivers saying "I got tripped by the TPWS at 265 signal but it was at 1 Yellow" only for the S&T to turn round and say "No, you got tripped by the OSS Plus for 267 signal which was at red"

 

• In some places the 'set speed' / 'trigger speed' of an OSS Plus installation may vary (which will of course affect the positioning of the individual loops), but in other areas like the Southern Region, the 'set speed' / 'trigger speed' of ALL OSS Plus installations is fixed at 65mph throughout the region.

 

Other Considerations

 

(i) Converging Routes

 

Where routes join up before they get to a signal fitted with it may be necessary to provide separate OSS installations on each route even if the TSS is common to both. Furthermore if each of the approaches have different characteristics then the spacing of the OSS loops and indeed any OSS + loops may well be different on each approach.

 

(ii) OSS used to enforce Permanent Speed Restrictions (PSR)

 

As the OSS is a speed sensing installation that can trigger the train brakes if a train is travelling too fast, it didn't take long before it was realised that it could be useful in ensuring compliance with PSRs. Thus you may find a TPWS OSS installation fitted which is completely unrelated to signals it seems to relate to - or out in a location with no signals at all! This PSR variant uses exactly the same kit as the OSS associated with signals - except with the loops constantly energised. Again placement will be determined by the exact speed restriction required for that location. As mentioned above, be aware that in some places these will be intermingled with OSS grids for signals making it difficult to determine what relates to what. If sited in close proximity to a diverging route then also be aware that OSS PSR installations can sometimes be linked to signal controls - e.g. a junction with a straight ahead route at 90mph and a diverging route with a 40mph speed restriction may well use a TPWS OSS installation to enforce the lower speed when the signal is set for the diverging route, but be turned off for the higher speed one.

 

(iii) Subsidiary signals (e.g. call ons)

 

On these installations the TSS will be deactivated when the position light illuminates or the mechanical shunt signal (yes TPWS is fully compatible with semaphore / mechanical signalling) is pulled off to a proceed. However as such moves are made at caution and from a standing start then the OSS and OSS Plus loops will remain active so as to ensure said train does indeed come to a stand first!

 

(iV) TSS Only Installations

 

As explained earlier the TSS itself is only helpful at low speeds, however if the signal it is fitted to applies to say the exit of a short freight branch restricted to 20mph say, then the TSS on its own may well suffice. As ever it all depends on what is necessary to prevent a train which passes the signal at danger from coming into conflict with other trains.

 

 

* Members of this forum who work for FOCs should be able to confirm what their TPWS timers are set to.

 

 

Edited May 23, 2020 by phil-b259

[TheSignalEngineer]

9 hours ago, Trog said:

 

Yes it was very annoying being told how to relay track by people who had only ever done it using components supplied by Hornby, and who would not have been able to recognise an F19 sleeper if you inserted it where the sun does not shine.

Thread drift alert.

 

I did have real respect for one of them. A very able engineer on his own field. The project was a sticky one and highly political. The lead engineers for each discipline were gathered together to meet him one morning.  His first words to us were "I know eff- all about building railways, that's up to you to get right. Just be truthful about the state of the job then leave the politics and money to me to sort out."

The project went from stumbling along from one crisis to another under his predecessor to a technical, political and PR success.

[Powerhaul 70 Pey]

6 hours ago, phil-b259 said:

 

 

Right, first the basics.

 

 

• TPWS is designed to prevent train collisions. It is NOT designed to prevent signals from being passed at danger!
• TPWS is fully compatible with mechanical signalling and there is no difference in how it is applied to the tracks.
• TPWS can be associated with signals AND to enforce enforce permanent speed restrictions.
• TPWS installations (note the 's') consists of an 'arming' loop which starts a timer on the traction unit and a 'trigger' loop. You cannot have a single stand alone loop for TPWS to work!
• The term 'grid' comes from the Fibreglass structural part - the loop itself is literally a loop of wire round the edge that forms a radio transmitter
• Each loop transmits a precise and specific (different for each type of loop) radio frequency which is picked up by an aerial under the train
• There is a timer on the traction unit FIXED at 1 second for passenger trains and slightly longer for freight*.
• If the traction unit passes over the 'trigger' loop before the timer has timed out then the emergency brakes come on and will not release until the traction unit has been stationary for 2 minutes.
• If the brakes are applied by the TPWS then the traction unit is said to have been 'tripped' by the TPWS

 

Now TPWS as applied to the track.

 

TPWS at any given location will usually consist of TWO, or sometimes three separate installations which work together to provide TPWS.

 

(1) A Train Stop installation (TSS)

 

• The 'arming' and 'trigger' loops are laid back to back in line with the signal. The layout of these loops will ensure that even a loco moving a walking pace will get a TPWS activation if it passes the signal at Red - as the FIXED timer on board the train (triggered by the arming loop) will not have finished timing out before the train aerial receives the frequency from the 'trigger loop'

 

• However on its own a trainstop installation will not prevent a collision if the train is travelling at any sort of speed (given how long it takes for trains to stop) when it gets tripped - and that brings us to the second component.....

 

(2) A Over Speed installation (OSS)

 

• This is designed to catch drivers who have NOT reacted to cautionary signalling aspects leading up to the red signal and who will be approaching a red signal at such a speed that the TSS will not be able to stop them before they come into conflict with another train.

 

• The OSS thus works on the principle of:- "Well the driver is coming up to a red signal, so at ZZ meters / yards back from the signal they should have reduced their speed to no more than XX mph"

 

• ....So...

 

• "IF the driver is travelling below XX mph then no intervention is required, but IF they are travelling above XX mph then we need to activate the emergency brake and stop them"

 

• Fortunately it is easy to do this with TPWS by adjusting the spacing of the 'Arming' and 'Trigger' loops. The further apart they are the faster a train can go without passing over the 'trigger' loop within 1* second of passing over the 'arming' loop.

 

• The 'trip' speed is carefully selected based on the braking curves that apply to that particular line for passenger trains (differences in braking characteristics between train types less of an issue due to the adoption of different length timers on EMUs / DMUs / locos undertaking passenger work and freight locos). The trip speed also must factor in the maximum line speeds allowed plus the ruling gradients that a train will encounter as it goes from green through the cautionary aspects to red as the laws of physics means its harder to slow a 60mph train going downhill than it is a 60mph train going uphill.

 

• Thus an OSS installation on a line where the 'trip speed' is 30mph will see the two OSS loops closer together, and closer overall to the signal to which they apply than a line which has a 50mph trip speed.

 

• It is thus important to note that the placement of OSS loops is thus bespoke to each site, determined by a complex set of calculations and NOT A SET DISTANCE! Modellers need to pay attention to this and appreciate you won't find any form of 'standard placing' to use.

 

• But to return to the real railway, the problem with an OSS is that at very high speeds (100+mph) the loops end up being so far back and so widely spaced that they won't provide protection for slower trains - who might be well under the 'set speed' / 'trigger speed' but would still not be stopped by the TSS installation at the red signal before coming into conflict with another train. Thus an OSS has limits on how far back from the signal to which it applies - and the limits chosen means it can only stop a train from coming into contact with another train if the train you want to stop is doing 75mph or less. Please note this does not mean all OSS installations are set for 75mph - most will be considerably lower, but 75mph is the absolute maximum for it to still be effective at doing the job it is designed to do.

 

(3) Over Speed Plus (OSS Plus)

 

• This will be fitted where the line speed is grater than 75mph - and in addition to the TSS and OSS installations described above. Again it uses 'arming' and 'Trigger' loops spaced a certain distance apart to trigger a FIXED timer on the train and activate the emergency brakes if it passes over the 'Trigger' loop within 1* second of being activated by the 'Arming loop'

 

• As with the ordinary OSS, the OSS Plus installation is based on the fact that drivers should be reducing their speed in line with the cautionary signal aspects and be preparing to stop - if they haven't then TPWS makes sure they do!

 

• Frequently the position of OSS plus loops end up being so far in rear of the signal they relate to that they actually end up encroaching into the previous signal section. There have been more than a few occurrences over the years of drivers saying "I got tripped by the TPWS at 265 signal but it was at 1 Yellow" only for the S&T to turn round and say "No, you got tripped by the OSS Plus for 267 signal which was at red"

 

• In some places the 'set speed' / 'trigger speed' of an OSS Plus installation may vary (which will of course affect the positioning of the individual loops), but in other areas like the Southern Region, the 'set speed' / 'trigger speed' of ALL OSS Plus installations is fixed at 65mph throughout the region.

 

Other Considerations

 

(i) Converging Routes

 

Where routes join up before they get to a signal fitted with it may be necessary to provide separate OSS installations on each route even if the TSS is common to both. Furthermore if each of the approaches have different characteristics then the spacing of the OSS loops and indeed any OSS + loops may well be different on each approach.

 

(ii) OSS used to enforce Permanent Speed Restrictions (PSR)

 

As the OSS is a speed sensing installation that can trigger the train brakes if a train is travelling too fast, it didn't take long before it was realised that it could be useful in ensuring compliance with PSRs. Thus you may find a TPWS OSS installation fitted which is completely unrelated to signals it seems to relate to - or out in a location with no signals at all! This PSR variant uses exactly the same kit as the OSS associated with signals - except with the loops constantly energised. Again placement will be determined by the exact speed restriction required for that location. As mentioned above, be aware that in some places these will be intermingled with OSS grids for signals making it difficult to determine what relates to what. If sited in close proximity to a diverging route then also be aware that OSS PSR installations can sometimes be linked to signal controls - e.g. a junction with a straight ahead route at 90mph and a diverging route with a 40mph speed restriction may well use a TPWS OSS installation to enforce the lower speed when the signal is set for the diverging route, but be turned off for the higher speed one.

 

(iii) Subsidiary signals (e.g. call ons)

 

On these installations the TSS will be deactivated when the position light illuminates or the mechanical shunt signal (yes TPWS is fully compatible with semaphore / mechanical signalling) is pulled off to a proceed. However as such moves are made at caution and from a standing start then the OSS and OSS Plus loops will remain active so as to ensure said train does indeed come to a stand first!

 

(iV) TSS Only Installations

 

As explained earlier the TSS itself is only helpful at low speeds, however if the signal it is fitted to applies to say the exit of a short freight branch restricted to 20mph say, then the TSS on its own may well suffice. As ever it all depends on what is necessary to prevent a train which passes the signal at danger from coming into conflict with other trains.

 

 

* Members of this forum who work for FOCs should be able to confirm what their TPWS timers are set to.

 

 

So much information , thank you very much for your time to do this!

[The Stationmaster]

1 hour ago, Powerhaul 70 Pey said:

So much information , thank you very much for your time to do this!

Hence you will realise from Phil's information that the TPWS 'grid' shown in your first photo is one of two as part of an OSS installation a considerable distance in rear of the signal to which it applies with that signal being out of view some distance to the left of your picture (all no doubt a consequence of the high linespeed).

[43110andyb]

[St. Simon]

Hi,

 

I answered a question about TPWS in this thread, I suggest we keep this one for cable troughing etc?

 

 

Simon

[phil-b259]

20 hours ago, Trog said:

 

Once the S&T started doubling up the track end cables to IBJ's each IBJ had four orange tubes running to it. The big problem was where there was a four track line with an IBJ in all four lines, that resulted in 16 pipes crossing the track nearest the troughing route in a matter of a few yards. This made the track un-tampable just at an IBJ where it needed it most.

 

 

There is no restriction on the number of cables which can be put through orange pipe (other than what will physically fit) so with thought it is possible to minimise the amount of pipe needed. The downside of course is if one pipe with lots of cables gets hit then you take out lots of equipment - and the whole principle of doubling up track connections for certain types of track circuit (others, like the TI21 variant for those in the know must only have a single set of track connections) is to provide redundancy (track circuit currents / voltages are not big enough to need doubling up electrically), then its logical to spread them out over several pipes.

 

Just one of the many conflicts between what the S&T and P-way departments ideally want....

[The Stationmaster]

On 22/05/2020 at 12:15, phil-b259 said:

 

There is no restriction on the number of cables which can be put through orange pipe (other than what will physically fit) so with thought it is possible to minimise the amount of pipe needed. The downside of course is if one pipe with lots of cables gets hit then you take out lots of equipment - and the whole principle of doubling up track connections for certain types of track circuit (others, like the TI21 variant for those in the know must only have a single set of track connections) is to provide redundancy (track circuit currents / voltages are not big enough to need doubling up electrically), then its logical to spread them out over several pipes.

 

Just one of the many conflicts between what the S&T and P-way departments ideally want....

I remember when orange pipes first came in and an S&T pal of mine said they weren't actually there to protect cables but to give the tamper operators a better target to aim at.

[Powerhaul 70 Pey]

Some location boxes and cable troughing (both Wills kits) and some orange piping ( capri sun drinking straws).  As I have seen some location boxes facing up/ down the line and parallel to the line I thought I would have a mix.

I am happy enough with them.

[RobertW]

Quote

On 20/05/2020 at 23:21, ajwffc said:

the one facing the track with the yellow stripe will contain scotches, clamps, point-handles(if u are lucky) and if you are very lucky blue roll.  

 

Not be pedantic, the cabinet with the yellow stripe is a FSP (Functional Supply Point). These come under the Electrification and Plant branch (although are subject to the same standards as signalling equipment), and are a sub-distribution point for the Signalling Power supply. There are multiple FSPs on a feeder, and Feeders can either be single ended radials (used for branches and sidings) or on double end fed feeders between Principal Supply Points.

 

Further details can be found here under PowerU FSP01/02, FSP03, FSP04.

 

Hope this helps, and please let me know if you have any questions or comments.

 

Rob

Edited July 16, 2020 by RobertW
edited to move photo into quote box

[e30ftw]

For the yellow bands ,100% correct but this has only started to apear in the last few years, depending on the region, and only on the main line in the areas i have experience with.

Although i have seen point clip and scotches kept in locs with a yellow band around them for the ops/MOMs

 

TPWS - at signals for the TSS , i doubt many layouts are big enough for OSS or OSS + grids : )

 

You can still find orange pipe around some redundent some still with cables in as its quite a chore to take out.

 

As for the troughs, they can always disapear under ballest near the track as the P way dump ballest over them over the years.