Northern extent of Southern Region 3rd rail in 1960s

[jim.snowdon]

11 hours ago, phil-b259 said:

 

The point is the potential difference!

 

+420 and -210 (which is how a 4 rail system is configured) gives a potential difference of 630V

 

+660V and 0V gives a potential difference of 660V (i.e. pretty much the same)

 

Post 1932 Southern an British Rail electrification schemes use a higher 750V rating to provide more power, but the inner suburban areas had to say at the lower 660V until either (i) The last of the pre 1932 electric stock (like the Bulleid 4-SUBs) was withdrawn or (ii) London Underground introduced their 'S Stock' which was designed to allow for an upgrading of the power supply to 750V (still split 2/3rds positive, 1/3rd negative)

I think the change to 750V on the Southern Region may have had to be held back until the last of the pre-1951 stock had gone. A clue is that getting electric stock down to Eastleigh under its own power, which has to be post 1967, was complicated by the higher line voltage used on the Bournemouth electrification. The requirement was, I think, that things like the series lighting and heating circuits had to be disconnected (by pulling the fuses) and driving limited to Series only in order to avoid putting the full voltage on the traction motors, the risk being commutator flashover.

 

As far as the LU stock (with which I was much much more familiar, having been an inmate of the CME's department), the traction equipments on the 1973 and D78 stocks were designed for 750V but, as it turned out later, the MA sets weren't, which prevented the Wimbledon and Richmond branches being brought up 750V until the D78s finished. The section of the Watford DC lines between Queens Park and Harrow is still stuck at 660V because the 1972 stock (only a year away from their half-centenary and showing their age) cannot cope with anything higher.

 

13 hours ago, Nearholmer said:

I am a railway traction power supply engineer, and you’ve got it pretty much right.

 

There are a few subtleties, in that creepage and clearance distances, especially around shoegear, which is in a cramped locations on tube trains, have not always been as great on fourth-rail trains as on third-rail trains, because they are designed to operate with split potential. The creepage and clearance distances should still be sufficient to operate with all potential on one pole, but there have been cases in the past where things didn’t go quite to plan, and flashovers occured at negative shoe gear, even when operating on split potential. LU suffered from a few incidents involving very, very nasty persistent arcing under train floors as a result of this in the 1940/50s. Modern trains have very carefully designed protection against this.

 

The LU system operates with the split in potential sensibly fixed by “ballast resistors” connected pole-earth-pole, and for many years has had monitoring systems to detect pole-to-earth faults and procedures to minimise the risk of coincident pole-earth-pole faults. I’ve long tried to discover exactly when the ballast resistors and fault detection were first fitted, and to discover whether the LNWR/LMS network in London had them, and I’m still not totally certain on either point.

 

 

The biggest problem with negative shoegear was when there was a positive earth fault (putting the negative at -630V) and persistent arcing due, for example to a damaged or loose cable connection (something colloquially known as a 'fizzer'). That is what took out the rear car (114, from memory) of a 73t/s train at Wood Green during the late 1980s, compounded by a failure of about five substations to 'see' sufficient current to trip the circuit breakers. LU did not, at the time, have inter-trip circuits between substations to cover for when the 'far' substation fails to see the fault.

The real Achilles heel of the older Underground stock was the shore supply plug, which was where both poles of the supply got to their closest. Before the C69 stock, the two pins were fixed into a single 'binocular' insulator moulding, with not many inches between them. The problems would start if this got damaged, for example, by the shed lead being forcibly pulled out - trains departing a shed with the rear car still plugged in were a perennial problem until at least the 1983 tube stock. If the insulator got cracked, which might not be visible, a track path would eventually establish between the two poles. The other problem with the older stock was that the main power leads between the shoes, the shed plug and the traction equipment were run in metal conduit. If a positive to negative fault occured, the arc tended to track back up the conduit, with the latter acting akin to a thermic lance. I can remember having to diagnose the cause of a similar event that occurred under an R stock car on the BR section of the Richmond branch, which by then was 650V +ve / 0V -ve, so that the arc went straight from the positive cable to the conduit, all initiated by a loose connection.

We did have occasional problems with the positive brushgear on the LT118 motors used on the D78s flashing over to the motor case. The clearance distance was about 20mm, but measured from the sharp corner of the brushgear aperture in the motor case to the equally sharp corner of the hex headed bolt that secured the brushgear. Once the corners had been rounded off by the arc, the electric field strength was reduced to workable levels and the problem usually didn't recur (on that motor).

 

Jim

[jim.snowdon]

On 11/06/2021 at 23:39, phil-b259 said:

 

No need for any fancy changeable stuff on board the train! As the LSWR proved when it Electrified the East Putney to Wimbledon section in partnership with the 4 rail District Railway  you simply bond the centre negative rail to the running rail.

 

i.e. an infrastructure solution rather than a train solution.

 

 

(Does rather make things a pain in the backside for S&T people though)

This is true, but the example I was thinking of was the interface between the lines of the ex-Wirral Railway and those of the Mersey Railway. The latter was electrified using 4th rail return (probably wise in view of the wet nature of the tunnels under the Mersey), whilst the LMS, when it electrified the Wirral Lines in 1938, opted for running rail return. The LMS 1938 stock was fitted with negative shoes and changeover switches.

 

One aspect of the LU/BR change points was the need, until the disappearance of the Q and CO/CP stocks, which had through bus lines, was the need for switched changeover sections at the boundaries - between Turnham Green and Gunnersbury, and across Putney Bridge. With the modern stocks, these were replaced by a 16m gap in both conductor rails, long enough not to be bridged by a single motor car. The same arrangement exists in the entrance to Stonebridge Park depot.

 

Jim

[phil-b259]

9 minutes ago, jim.snowdon said:

I think the change to 750V on the Southern Region may have had to be held back until the last of the pre-1951 stock had gone.

 

My understanding was that the generally higher power requirement for express electric services to the likes of Brighton, etc (as opposed to trundling round the London suburbs) was the driver for a higher voltage and this was done by the Southern Railway for their late 30s electrification schemes. Areas already done at 660V stayed that way of course and given London suburban units received repairs at depots within that area (e.g. Slade Green) the inability to get to Eastleigh / Lovers Walk wouldn't have been that much of an issue.

[jim.snowdon]

10 hours ago, Nearholmer said:

25kV/DC interfaces can get complex and expensive too, especially if signalling system immunisation questions come into the equation, which they may have if the third rail crept that extra few hundred metres.

The greatest complication can come from the incompatibility of an earthed AC system and the floating DC system. Connecting the running rails on DC tracks to Earth at the wrong place can result in alarmingly large currents flowing. Although the running rail to earth voltages are relatively low, the impedances involved are small.

 

7 hours ago, The Stationmaster said:

When the through local passenger electrified passenger service started over the WLL it was quite amusing to stand in the International depot control room and watch the EMUs come to a stand. more or less opposite,  just south of the GWML bridge, in order to changeover from 25kv overhead to the 3rd rail current collection.  it always struck me as very peculiar that they didn't/couldn't manage it while moving.

They could, and sometimes did, but the instruction from Southern Trains was that the changeover must be done whilst stationary.

 

In any case, NR, if not also Railtrack, had a thing about not raising pantographs on the move for a long time until coasting was eventually authorised for the ECML to get trains past sections that had OLE defects. This is despite it having been common practice in Europe for much longer, not to mention instances on the Pennsylvania RR system where the OLE is gapped for lifting bridges and the pantographs are simply allowed to rise to their limits off-wire, and then pick up the wire again on the far side, all whilst the train is running at line speed.

 

Jim

[jim.snowdon]

25 minutes ago, phil-b259 said:

 

My understanding was that the generally higher power requirement for express electric services to the likes of Brighton, etc (as opposed to trundling round the London suburbs) was the driver for a higher voltage and this was done by the Southern Railway for their late 30s electrification schemes. Areas already done at 660V stayed that way of course and given London suburban units received repairs at depots within that area (e.g. Slade Green) the inability to get to Eastleigh / Lovers Walk wouldn't have been that much of an issue.

I have a reference (Electric Traction by J G Haut, Vol 2) that the Southern didn't start increasing the voltage to 750V until after World War 2, and my 1954 edition of Dover's Electric Traction refers only to 650V in connection with the Southern Region. That would suggest that 750V did not arrive until the 1956 Kent Coast electrification.

 

Jim

[phil-b259]

33 minutes ago, jim.snowdon said:

 

In any case, NR, if not also Railtrack, had a thing about not raising pantographs on the move for a long time until coasting was eventually authorised for the ECML to get trains past sections that had OLE defects.

 

 

I think the logic was if the changeover was done while stationary but was unsuccessful then the train could revert to the previous supply and be reversed out the way relatively easily (the WLL is bidirectional signalled throughout).

 

If the changeover is done on the move however and a problem occurs then there is a danger that the train would come to a halt beyond the end of the OLE or Con Rail and become stranded due to not being able to use the power source present and need rescuing by another unit.

 

This risk can of course be mitigated by ensuring that the overlap between both systems is long enough to cover the eventuality of a 'on the move' changeover not working - but that could turn out to be very expensive, particularly if it means lots of expensive signalling immunisations are subsequently required which wouldn't have been needed with a shorter overlap.

 

The logical place to do such changeovers is of course stations - and its a real shame a way cannot be found to bring the OLE a bit further south to Shepherds Bush station where all Southern and LO trains stop anyway.

 

 

[The Stationmaster]

9 hours ago, jim.snowdon said:

 

In any case, NR, if not also Railtrack, had a thing about not raising pantographs on the move for a long time until coasting was eventually authorised for the ECML to get trains past sections that had OLE defects. This is despite it having been common practice in Europe for much longer, not to mention instances on the Pennsylvania RR system where the OLE is gapped for lifting bridges and the pantographs are simply allowed to rise to their limits off-wire, and then pick up the wire again on the far side, all whilst the train is running at line speed.

 

Jim

Certainly so in Railtrack days Jim although whether it was them or train operator conservatism I wouldn't know.  But if you mentioned it to Railtrack folk at meetings there was always a lot of doubtful shaking of heads and looks of wonder/terror when you told them them what happened day-in-and-day-out in France and at various border stations where trains ran through at line speed.

[Oldddudders]

10 hours ago, jim.snowdon said:

They could, and sometimes did, but the instruction from Southern Trains was that the changeover must be done whilst stationary.

Silverlink's Fleet Manager was known to suck his teeth a bit when tales of changeover on the fly were reported.....

[The Stationmaster]

5 hours ago, Oldddudders said:

Silverlink's Fleet Manager was known to suck his teeth a bit when tales of changeover on the fly were reported.....

Hilarious when you think that Eurostar Class 373s were permitted to change between overhead and 3rd rail, or vice versa, while running up to line speed on 100mph infrastructure.   However that was not entirely without its problems as the 3rd rail shoes were for some while not exactly 100% reliable when it came to retracting and as they were out of gauge in the running position on SNCf so could, and did hit ground mounted signals.  To deal with that problem SNCF installed a nice block of concrete on their side of the boundary with Eurotunnel at exactly the right height to 'remove' any shoes which had not fully retracted.

 

Coming the other way the opposite problem was obviously going to be the possibility of a pantograph not being lowered, or going overheight as it came off the overhead.  Sandling station footbridge I believe still shows the scars  of the actions ofa somewhat confused SNCF Driver who for reasons known only to himself decided to chanmge back to pantograph power collection as his train emerged from Sandling Tunnel.  The signal gantry at the Continental Jcn end of that tunnel also at one time displayed the of an unlowered pan which went overheight and collided with it - the signal gantry won (as did Sandling footbridge apart fro a few pieces knocked out of it).

[Pacific231G]

On 12/06/2021 at 09:47, Nearholmer said:

I am a railway traction power supply engineer, and you’ve got it pretty much right.

 

There are a few subtleties, in that creepage and clearance distances, especially around shoegear, which is in a cramped locations on tube trains, have not always been as great on fourth-rail trains as on third-rail trains, because they are designed to operate with split potential. The creepage and clearance distances should still be sufficient to operate with all potential on one pole, but there have been cases in the past where things didn’t go quite to plan, and flashovers occured at negative shoe gear, even when operating on split potential. LU suffered from a few incidents involving very, very nasty persistent arcing under train floors as a result of this in the 1940/50s. Modern trains have very carefully designed protection against this.

 

The LU system operates with the split in potential sensibly fixed by “ballast resistors” connected pole-earth-pole, and for many years has had monitoring systems to detect pole-to-earth faults and procedures to minimise the risk of coincident pole-earth-pole faults. I’ve long tried to discover exactly when the ballast resistors and fault detection were first fitted, and to discover whether the LNWR/LMS network in London had them, and I’m still not totally certain on either point.

 

 

Hi Kevin 

it  wasn't he traction circuits themselves I was thinking of but more that the higher voltage between the pickups etc and the earthed chassis would require greater insulation, whether in the actual insulation of cables and equipment or by air gaps.  In terms of avoiding eddy currents etc, in surrounding pipes and the actual tube tunnels I'm guessing that the fourth rail return could be at zero volts with respect to earth provided it wasn't actually earthed. 

I know why the tube used four rail electrification but would that have ever been necessary if all the lines had been sub-surface.  

 

BTW ISTR that one or two of the early Paris Metro lines used a third rail with an overhead return but I'd have to delve into the library to find out what the actual voltages were. I don't think the overhead was very high (in both senses) and the pantographs were decidedly miniature. 

 

 

[Nearholmer]

In the Underground split potential system, each pole on the train is fully insulated from earth (solid insulation, clearances in air, and creepage distances), so as to withstand the full pole-to-pole voltage, and transient voltages that exceed that, because under single pole-to-earth fault conditions, which are relatively common (old bike frame thrown on the track etc.), that is what it experiences. But, as both JS and I have highlighted, on some of the old tube stocks, there were weaknesses, points that were vulnerable to faults, either pole-to-pole, or pole-to-earth-to-pole.

 

10 minutes ago, Pacific231G said:

In terms of avoiding eddy currents etc, in surrounding pipes and the actual tube tunnels

 

Eddy currents are generally an a.c. induced phenomenon, so you are probably thinking of stray currents, and yes, from that point of view the potential of the conductor rails is immaterial, provided that they aren't accidentally connected to earth. The 2/3 - 1/3 voltage distribution seems to have begun as the natural product of tall positive insulators, and short negative ones, presenting different creepage resistances, and then later to have been "nailed" by using "ballast resistors".

 

15 minutes ago, Pacific231G said:

early Paris Metro lines

 

They had a very unusual (unique?) split-potential arrangement. Going from memory, because I CBA to look it up either, I think it was 600-0-600, with one traction package on each set connected positive-to-centre, and the other centre-to-negative, so nothing experiencing 1200 by design, so it was a three-wire dc system (not three-phase, which is something else altogether), like contemporary dc street lighting mains. I'll try to remember to check later.

 

The use of multi-wire low voltage dc distribution for traction was a sort of desparate measure before high voltage ac distribution was introduced, because it was the only was the only way to transmit large power over reasonable distances without either massive voltage drop or massive cables. The city & South London Railway got really carried-away with it as the line and traffic expanded, and they had to distribute at low voltages from one power house at Stockwell. They ended-up with either a five of seven wire system (again I need to check), with the up and down road conductor rails connected to different potentials, and a baffling array of booster sets distributed about the place.

[Pacific231G]

On 10/06/2021 at 00:02, Hal Nail said:

The Clapham Junction, Olympia, Willesden line was used for services between Brighton and the North but trains still switch from overhead to third rail just south of Willesden, so that might be the limit.

 

The Southern part of Reading was essentially a separate station (albeit alongside) for many years and I think still was in the 60s. 

As Compound2632 has said. Reading (Southern) was a completely separate station from Reading General, though very close to it, until September 1965 when it was closed and its trains diverted into Reading General which had acquired a new third rail platform 4a. That was not before I travelled via it from Oxford on a school railway society  shed bashing trip to Guildford on a diesel "thumper. It was a delightful compact terminus positively oozing Southern Railway atmosphere and, with four platform faces, almost a Minories or the sort of suburban terminus that Edward Beal always seemed to have on his  West Midland Railways.  I was really sorry to see it close which happened a few months after the (Great) Western Region got their claws on it.  

[Pacific231G]

23 minutes ago, Nearholmer said:

 

 

The use of multi-wire low voltage dc distribution for traction was a sort of desparate measure before high voltage ac distribution was introduced, because it was the only was the only way to transmit large power over reasonable distances without either massive voltage drop or massive cables. The city & South London Railway got really carried-away with it as the line and traffic expanded, and they had to distribute at low voltages from one power house at Stockwell. They ended-up with either a five of seven wire system (again I need to check), with the up and down road conductor rails connected to different potentials, and a baffling array of booster sets distributed about the place.

 

Hi Kevin 

Early electrification is fascinating . 

Slightly OT but some of the early rural electric tramways in France used fairly terrifying AC voltages, given that they were running  down the streets of villages and small towns. It did mean that they could supply lines of up to a hundred kilometres  or so from one end. The Haute Vienne system, built in 1908, operated on 10kV at 25Hz  with all four of its lines supplied from feeders on the edge of Limoges.  Inside the city it used a 600V 25Hz supply with a switchable feed to the primary coil of the motor car's onboard autotransformer (I think the actual motors were 300V supplied in pairs in series with up to 600V from various voltage taps using  a drum type controller)  The 10kV feeder for each line, which were electrically sectioned about every ten kms. was mostly carried on wires above the catenary system and, so far as  I know, was on a single phase for each line.  The only transformers out in the country were those that reduced the traction voltage to a domestic level (~200V I think) to supply electricity to the towns and villages it passed through. Using electric traction meant that the very hilly Département could use far steeper gradients for its rural tramways than steam could have handled and that cut the construction costs by more than enough to justify the electrical infrastructure. It was not though without its problems. The system's controller, who was based in Limoges with an omnibus phone for each line, apparently  stood or had his seat on a thick rubber mat! 

[Nearholmer]

I became aware of that system when we holidayed a bit further south, and passed through somewhere where one of its tentacles finished. The phones out in the country were in call boxes standing on insulating blocks, so that the user was “a bird on the wire”. It ran through a village where the nazis massacred the population and destroyed the place, which is still there in ruins as a monument, and bits of the OHLE still exist.

 

Didn’t we discuss this before?

[Hal Nail]

1 hour ago, Pacific231G said:

As Compound2632 has said. Reading (Southern) was a completely separate station from Reading General, though very close to it, until September 1965

Was there a link between the old Southern and GWR routes pre '65?

[Oldddudders]

29 minutes ago, Hal Nail said:

Was there a link between the old Southern and GWR routes pre '65?

Very much so, but it didn't link the stations. trains heading into Reading went either to one or the other. 

[jim.snowdon]

5 hours ago, Pacific231G said:

it  wasn't he traction circuits themselves I was thinking of but more that the higher voltage between the pickups etc and the earthed chassis would require greater insulation, whether in the actual insulation of cables and equipment or by air gaps.  In terms of avoiding eddy currents etc, in surrounding pipes and the actual tube tunnels I'm guessing that the fourth rail return could be at zero volts with respect to earth provided it wasn't actually earthed. 

At the voltages with which we are concerned, the thickness of the insulation is usually determined more by mechanical considerations, ie robustness, than it is by its electrical properties.

5 hours ago, Pacific231G said:

I know why the tube used four rail electrification but would that have ever been necessary if all the lines had been sub-surface.  

In the beginnng, only the Yerkes lines* and the Great Northern & City Railway used four rail electrification. The Central London, Waterloo & City and City & South London railways all used 3rd rail only. The CLR and the W&CR were conventional, but the C&SL electrification was actually a three-wire 1100V system - +550 / 0 / -550 - with the north- and southbound running lines being the opposite poles of the supply.

 

The 4th rail system originated on the surface lines of both the Metropolitan/Metropolitan District companies and the Mersey Railway, where its real assets were not only the avoidance of stray current but also the convenience of keeping the traction power separate from the signalling track circuits. The Met & MDR were early users of electric track circuits for their signalling, and at the time, the impedance bond had yet to be invented.

 

*in modern terms, the Bakerloo, Piccadilly and Northern lines.

 

Jim

[jim.snowdon]

5 hours ago, Pacific231G said:

Slightly OT but some of the early rural electric tramways in France used fairly terrifying AC voltages, given that they were running  down the streets of villages and small towns.

The British, it would seem, were besotted about tramway electrification not harming the horses with which they shared the streets. I'm not certain precisely where the relevant statute lies, but it was illegal to string bare wires carrying more than, originally, 550V DC above the street. These days, 750V is allowed, but no more. It is one reason why any thoughts of street running in the original Tyne & Wear Metro schemes were abandoned, and there were, in its early days, thoughts about Manchester Metrolink using 1500V off street and 750V on street, with the trams designed to operate off either by the driver selecting on-street and off-street operating modes.

 

Jim

[Pacific231G]

6 hours ago, Nearholmer said:

I became aware of that system when we holidayed a bit further south, and passed through somewhere where one of its tentacles finished. The phones out in the country were in call boxes standing on insulating blocks, so that the user was “a bird on the wire”. It ran through a village where the nazis massacred the population and destroyed the place, which is still there in ruins as a monument, and bits of the OHLE still exist.

 

Didn’t we discuss this before?

I think so. The tramway's installations within Oradour-sur-Glane are complete including about a kilometre of the track and OLE through the village and all the pointwork at the station.

 

The OLE may not though be entirely what was there at the time of the massacre. The CDHV continued to run through the "martyred village" for a few years after the war till it closed in 1949 so the damage it muist have suffered when the village was burnt was repaired.  In  the end the road through the village was diverted so that it could become a memorial site with entrances at each end. However, as long as the tramway remained open, the station which is near the north end of the original village, continued to be used. I assume that is why the goods shed seems to be the only undamaged building in the village.

 

A new Oradour was built a little to the north but the station was never moved there.

 

I've visited Oradour a couple of times and it did feel almost sacrilegious to be too interested in  railway installations there. On the other hand the tramway and its station was part of the daily life of this completely ordinary French community where 643 perfectly innocent people, including 205 children were murdered just four days after D-Day.

(Both photos are copyright and were taken by me in 1997)

 

 

Edited June 14, 2021 by Pacific231G

[Compound2632]

13 hours ago, Hal Nail said:

Was there a link between the old Southern and GWR routes pre '65?

 

Yes. This is the 1914 RCH Junction Diagram sheet showing Reading. There had been through carriage workings for many years before this and of course a good deal of goods and mineral traffic was exchanged. I'm slightly surprised to see that short section of the link marked as being LSWR property; I'm not sure I believe that, having seen some oddities in other RCH diagrams.

 

[jim.snowdon]

1 hour ago, Compound2632 said:

 

Yes. This is the 1914 RCH Junction Diagram sheet showing Reading. There had been through carriage workings for many years before this and of course a good deal of goods and mineral traffic was exchanged. I'm slightly surprised to see that short section of the link marked as being LSWR property; I'm not sure I believe that, having seen some oddities in other RCH diagrams.

 

Yes, it is rather odd, but not implausible. Interestingly, the Running Powers section of the 1914 RCH Diagrams book gives the following for the LSWR, in addition to the blanket Wokingham Junction to Reading Station power, Reading, SE&C Junc. with L&SW - SE&C Junc. with Reading Line. I'm not certain how to interpret that, but the pertinent point is the reference to a junction with the L&SW.

 

[Nearholmer]

Is odd, isn’t it. Was there some point in the dim and distant when LSWR services vis Ascot terminated in the GWR, rather than the SER station? 

[Compound2632]

7 minutes ago, Nearholmer said:

Is odd, isn’t it. Was there some point in the dim and distant when LSWR services vis Ascot terminated in the GWR, rather than the SER station? 

 

I shouldn't think so. The original connection was via the GW goods yard - lines burrowing under the GW main line; the lines up the south side of the GW embankment - now the access to the three-platform replacement for the old platforms 4A and 4B of not so fond memory* - were put in when the through trains between the GCR and the SECR started, early in the 20th century (IIRC - not checked dates).

 

*I commuted from them at 7:29am daily for several years in the late 90s.

[Nearholmer]

11 minutes ago, Compound2632 said:

commuted from them at 7:29am

Slugabed.

[jim.snowdon]

14 minutes ago, Compound2632 said:

 

I shouldn't think so. The original connection was via the GW goods yard - lines burrowing under the GW main line; the lines up the south side of the GW embankment - now the access to the three-platform replacement for the old platforms 4A and 4B of not so fond memory* - were put in when the through trains between the GCR and the SECR started, early in the 20th century (IIRC - not checked dates).

 

*I commuted from them at 7:29am daily for several years in the late 90s.

In terms of what is on the large scale OS maps, the 'modern' double track connection was put in between the 1900 and 1912 surveys. What is known is that in 1898 the GWR built two pairs of slip carriages specifically for the Liverpool - Folkestone service and that these were transferred from the GWR to the SECR at Reading. Quite how is not clear, as the transfer time at Reading in the southbound direction was 2 minutes, but 27 minutes in the northbound direction. The inference is that, southbound, they were slipped at Reading GWR, and attached to an SECR train that started from Reading GW. The northbound transfer, which was at around 01:00, would appear to have either involved a long shunt, or a long wait for the connecting train that would take them on to Liverpool.

 

Jim