Signalling Installation Handbook.

[andyrail]

Does anyone know where I can get the most recent Signalling Installation Handbook? Thanks.

[Peter]

Does anyone know where I can get the most recent Signalling Installation Handbook? Thanks.

Network Rail make all of there standards available via a subscription service offered by IHS.com which effectively means you have to pay. They impose the duty on the subscriber not to copy or distribute standards which means that I cannot pass one on to you.

The recent version that you talk about is probably NR/L3/SIG/11303, however, there is not that much new in it compared with the old RT/E/C/11210. The new version is merely a reformatting which makes the standard into an index with each of the individual sections as separate stand alone appendices. The vast majority of the appendices are unaltered from the earlier issue. This has been done so that they can update the appendices gradually without the need for re-issuing the entire standard each time. There are only a few updates to the appendices that existed and there are a couple of new ones for equipment which was not around when the original standard came out.

If you have a copy of the old one, you have most of the information in the new one, but this does not mean that you have up to date information - it is still horribly out of date even though re-published!

Peter

[andyrail]

Thanks Peter , I have heard IHS mentioned in the office before so I think they must have an account. Most helpful.

Andrew

[andyrail]

When DC single rail track circuits are used due to one of the rails being used as a return conductor ,all the track circuit leads are still connected onto both rails how is it that the pos and neg from the abutted trackcircuits don,t affect each other.
What is the level of traction return current that flows though the return rail?
Why does it not effect the track circuit ?
I,ve looked on line for a simple answer to this but have failed to find one, I install these single rail Track Circuits all the time and wonder ,how can that pos and that neg from different track circuits be right next to each other without a block joint, and then add the traction return current into the mix.
Can anyone help with my confusion on this subject ,please try to make as simple as possible. Thanks.

[PJW]

When DC single rail track circuits are used due to one of the rails being used as a return conductor ,all the track circuit leads are still connected onto both rails how is it that the pos and neg from the abutted trackcircuits don,t affect each other.

This is actually a very sensible question, but I am afraid the answer isn't simple but I have tried my best to express it without too much complication.

The first answer is: because they are not otherwise connected- they are separate batteries (or more likely the output of different transformer rectifiers). You are perfectly right that it wouldn't work if fed from one common N6 / B6 supply distributed from loc to loc via a cable!

Think of putting three 1.5V batteries in a torch to give a 4.5V supply; this entails connecting the positive of one battery onto the negative of the next and thus the three 1.5 sum to a total of 4.5V; think of the middle battery- this will be touching the negative end of the first battery and the positive end of the last battery, but it is not shorted out is it?
The positive and negative of a battery are relative to each other but have no absolute significance. No current flows if you simply put a wire between one end of a battery and one end of another- there is not a complete circuit.

So when you put a positive and a negative lead on the same rail without a block joint between them, this is the ONLY connection between them. What you will find though is that the voltage measured across the opposite insulated rail joint is approximately TWICE the voltage of the two separate tracks (just like the batteries in the torch summing to give the grand total).

What is the level of traction return current that flows though the return rail?
Why does it not effect the track circuit ?

Very large (many 100s if not 1000s of Amps) in the case of 3rd rail dc traction railway, generally shared across both rails of a track and indeed amongst other parallel lines as well.
Rather lower but still large in the case of 25kV ac overhead traction (since voltage is so much higher and the use of booster transformers sucks it up as soon as possible into the elevated return conductor).

To some extent it certainly DOES affect track circuits but this is minimised by careful design.
This is the reason why we use:
dc tracks in ac traction areas and
ac tracks in dc traction areas.

Effort also goes in to making the dc tracks as immune to ac as possible; the design of the relay encourages the changing magnetic field to be diverted rather than appear across the armature air gap and thus falsely operate the relay. This effect could eventually be overcome if the ac voltage was large enough, but this would cause so much heat dissipation that the relay coil would very rapidly burn out and thus act as a fuse so relay can't remain falsely energised for a significant time.

Conversely ac vane relays certainly require an ac flux to set up eddy currents in the vane in order for these to rotate and operate the relay and pure dc can't do this; the problem is that the dc isn't pure. Harmonics of the mains frequency from which the dc is produced is one problem, but the real killer is the interference that can be produced by modern trains with their semiconductor variable frequency drives. There have been various approaches (the slow to operate modifications to desensitise tracks when the Eurostar train was introduced) but really the solution is a more sophisticated track circuit such as HVI or TI21 / Ebitrack 200 that need a very specific waveform.

The greatest problem actually tends to be getting the impedance bonds to be as low resistance as possible for getting the traction current to flow around the insulated block joint, yet have a high enough impedance to the track circuit frequency that it isn't shorted out by the equivalent of very low ballast resistance.

So in short and make it as simple as possible-
IT IS DIFFICULT but the trick is to make the track circuit insensitive to the very much larger traction currents; this is only possible if they are of different nature,
it is a bit of a black art and the sort of thing that makes one think that axle counters seem a very good idea!

I've looked on line for a simple answer to this but have failed to find one, I install these single rail Track Circuits all the time and wonder, how can that pos and that neg from different track circuits be right next to each other without a block joint, and then add the traction return current into the mix.

Can anyone help with my confusion on this subject, please try to make as simple as possible. Thanks.

Hope this helps; can anyone explain better?

[PJW]

No problem.
I expect some of the people you asked didn't actually understand themselves!

Thanks PJW, your explanation was very clear even for me as a layman and the penny really dropped when you used the torch batteries as an example ,it was one of them ,"Oh yer " moments. Not the first time I,ve asked this question but this is the first time I think the answer given has given me a clear insight ,rather than more confusion. Once again ,Thanks.

[Peter]

When I started installing DC track circuit pre moulded leads to the rail in 1997,the arrangment for the connection of the pre moulded leads on the tamper pin was as follows - Lead onto the pin with nothing between rail and moulded end ,then a washer and locking nut.
Now some are of the opinion that this has changed and that pre moulded leads use the same arrangment as L plate connectors which is washer and nut onto the pin,then the L plate ,then washer and locking nut

---

Does anyone know the current standard for connecting a pre moulded DC t/c lead to the rail?

The installation handbook has not been updated on this, but the equipment has. We had a long discussion about this when using moulded leads with other types of track becasue there was the comment that we were not using the back nuts before putting the moulded end on the taper pins.

It appears that there was a mod to the moulding which created a recess making it possible to fit a backnut. However, what was clear was that this was never really communicated and the standards were not updated to reflect it. I was having the converstation with the excellent Mr Fortey before he retired from NR and he knew about the mod but could not cite revision to the standard.

There is a further twist here in that before the recessed version was made, in order to allow a back nut to be fitted, there was a longer version of the taper pin. This has a BRS-SE number and a PADS cat no, but is not supplied by Unipart, so making it effectively useless.

So the answer to your question is that the standard tells you to do what you have always done, but that is not the right thing to do!

Peter

[Peter]

Thanks Peter, your explanation explains why their are are 2 differing views on this subject . I think I,ll just carry on as I always have done but with the constant knowledge that every now and then some rebel will tell me I forgot my back nut.
My reply will be,"Don,t forget your bible!

The problem is that if you don't put the back nut on them and the lead has the recess, there is not anything firm that gets held between the front nut and the rail as the metal sleeve is not pressing on the rail and the rubber can give.

[gear259]

Thanks Peter, your explanation explains why their are are 2 differing views on this subject . I think I,ll just carry on as I always have done but with the constant knowledge that every now and then some rebel will tell me I forgot my back nut.
My reply will be,"Don,t forget your bible!

The problem is that if you don't put the back nut on them and the lead has the recess, there is not anything firm that gets held between the front nut and the rail as the metal sleeve is not pressing on the rail and the rubber can give.

 Has there been any further movement on this? Back nut will still not fit, but the debate now is back washer or not? Personally, I think the backwasher is needed to provide continuity and support on the back. There is a slight recess still, and if you don't fit back washer is seems a bad job.  However, there's a strong thought by some that there should be no back washer as they can somehow vibrate and cause track faults.  I don't see how this can be true, otherwise surely the locknut would be loose, and how would a back washer cause additional vibration that the front washer or no back washer at all. 

Has anyone heard of a back washer being a cause of fault?
What is official standard now?