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electrified 3rd rail and non electrified 3rd rail


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Posted (edited)
1 hour ago, jim.snowdon said:

The other assumption that I am making is that the DC negative return rail is not connected to earth, as is standard practice with third rail electrification. It would, when the fourth rail was in proper use, have been connected to earth


I’m sure that this question, and the rest of the subject of this thread, has been discussed before in a near-identical thread.

 

Despite searching for evidence one way or the other, I cannot recall having seen any conclusive evidence that the -ve return rail of the LNWR four-rail electrification was connected to earth. It would have been a potentially very trouble-causing thing to do, and would have been at odds with practice on other four-rail electrified lines, and I remain sceptical about it ever having been connected to earth, except possibly via “ballast resistors” designed to ensure a predetermined relationship between +ve to earth and -ve to earth voltages.

 

The fact that the negative CR was located on insulators, and set to the same standards as that on the Met and District Rlys suggests very strongly indeed to me that it wasn’t directly earthed.

Edited by Nearholmer
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On 4-rail systems (more correctly insulated return systems), it is normal for one running rail to be connected to earth for basic electrical safety. It removes any risk of the car body becoming live with respect to either conductor and Earth. (A problem that is altogether more significant for trolleybuses.) The other running rail is used for signalling purposes. From memory, there weren't many four rail electrifications in Britain - ignoring the conduit tramways, I can only think of the Metropolitan/District, London Electric Railways (the Yerkes tubes), the GN&C and the Mersey Railway.

 

Jim

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Posted (edited)
17 minutes ago, jim.snowdon said:

one running rail to be connected to earth for basic electrical safety


True.

 

But from what you wrote earlier, I thought you were talking about the ‘DC negative return rail’, which in a four-rail system is a conductor rail, not a running rail.

 

The only other ones I can think of are the some odd industrial railways. The L&Y 600V and 1200V systems had what looked like four rails, but I’m pretty certain the fourth rail was a reinforcement for the running-rail return, bonded to the running rails.

 

 

Edited by Nearholmer
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10 minutes ago, Nearholmer said:


True.

 

But from what you wrote earlier, I thought you were talking about the ‘DC negative return rail’, which in a four-rail system is a conductor rail, not a running rail.

 

The only other ones I can think of are the some odd industrial railways. The L&Y 600V and 1200V systems had what looked like four rails, but I’m pretty certain the fourth rail was a reinforcement for the running-rail return, bonded to the running rails.

 

 

I see your point. It's something of a case of when is a negative rail not a negative rail as a result of not being clear enough.

 

As built, with 4-rail electrification, the rails would have been (reading across the track) -

- positive conductor rail

- earthed running rail* (electrically continuous)

- negative conductor rail

- signalling running rail* (divided by IRJs into signalling track circuit sections)

 

* I am not 100% certain that they were this way round, but it appears logical and would be consistent with later events.

 

When converted to 3-rail electrification, the rails would have been -

 

- positive conductor rail

- negative running rail (electrically continuous)

- negative conductor rail (if present, bonded to the negative running rail) - retained only for LUL stock and to reinforce the negative return path.

- signalling running rail (divided by IRJs into signalling track circuit sections)

 

Normally the negative running rail would be disconnected from earth, but with the line's past history and the overlap with the AC electrification from Camden into Euston I am not 100% sure. Between Camden and Euston, the DC negative rail will also be the AC return rail and normal practice is for that to be earthed via all the structures, with the result that DC return current to Camden substation may be wandering all over the place. From the junction with the Slow Lines just outside Primrose Hill tunnel the DC lilnes are physically separated from the AC lines all the way to Watford Junction, where the connection onto the Down Main line and into the station platform is provided with a 2-pole switch that should be normally open (the isolation diagrams show it as closed, I believe incorrectly - questions have been asked). One pole is for the positve feed to the conductor rail in the Down Main platform, the other is the negative, which if closed will earth the DC lines negative at the Watford Junction end.

 

Jim

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3 hours ago, Pete the Elaner said:

 

Interesting to hear when the 4th rail was last used.

I have some old photos in a book about the Euston-Watford line showing South Hamsptead & Kilburn High Road with 4th rail (but it isn't there now) so I assumed this must also have continued to Euston.

When did it get lifted south/east of Queen's Park?

I stand corrected over the 501's, which were in all fairness withdrawn before I was born!! There are significant sections, practically the whole way from Watford Junction to Carpenders Park where there is no 4th rail at all, there are some very rusty old lumps of it left principally Hatch End to Harrow and these are bonded in places to the running rail adjacent to the conductor rail, but never to another bit of old 4th rail even where a short gap appears in the 4th rail. Its all on the deck, none of it on pots, no insulation and not aligned to the centre at any point except where it happens to cross the centre whilst laying diagonally. The Class 313's certainly didn't use it.

 

4th rail still in place Kilburn High Road up platform and everywhere north thereof as its needed for Bakerloo turn back.

 

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23 hours ago, bigherb said:

Got a feeling the bay platform at Oxted for the Uckfield trains is not electrified.

The bay at Uckfield is not fully electrified as the deep layer of rust on the third rail would probably prevent any juice being picked up !

 

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I’d never thought of Sanderstead as an oasis, but it’s a good one for this, and it had rather nice signals. IIRC the up starter had a distant arm for the next box.

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22 hours ago, cg501 said:

Is the Bay platform (5) at Basingstoke electrified, I used to remember that the DEMUs from Reading coming in to the bay and those lines which were not electrified. It used to be a straight though platform but was cut back so that the station had better access from the northside. 

 

Andrew

The Reading bay at Basingstoke is not electrified, as it only has access to the Reading line.

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9 hours ago, Nearholmer said:

I’d never thought of Sanderstead as an oasis, but it’s a good one for this, and it had rather nice signals. IIRC the up starter had a distant arm for the next box.

Now, before you get to the next ( South Croydon ) 'box you come to the delights of Selsdon ( Junction ) which might fit the OP's bill !  The electrified Woodside and South Croydon veers off to the right with a single platform for a peak-hours only service and a back-shunt into the old goods yard for oil traffic while the 'main' Oxted Line passes between the remnants of its long-disused platforms and drops down to the aforementioned 'box and back onto third rail territory. It's not all MUs, of course, as there were a handful of Crompton-hauled business trains between East Grinstead & London Bridge.

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Posted (edited)
On 18/05/2020 at 14:07, cg501 said:

Is the Bay platform (5) at Basingstoke electrified, I used to remember that the DEMUs from Reading coming in to the bay and those lines which were not electrified. It used to be a straight though platform but was cut back so that the station had better access from the northside. 

 

Andrew

I think the obvious connection between the eastern and western bays at Reading, to give another electrified route to Blazingsmoke, was rather thwarted when some guy called Brunel plonked a Grade II listed station building in the vicinity.

Edited by Wickham Green too
clarification
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I thought Selsdon was the next box after Sanderstead.

 

Really ought to remember, because I spent enough time staring out of the window looking at weed-grown platforms when I commuted that way for c10 years. Up trains were always held waiting a path at South Croydon, and Down trains often had to wait for the electric to cross over at Sanderstead.

 

In those days we had at lease one, sometimes two, Crompton-hauled trains to Uckfield too and, with everything semaphore signalled from a delightfully varied selection of boxes, the entire route had a good deal of old-railway atmosphere.

 

You are right that with the rose-tint of forty years distance that little area would make a very characterful model.

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Apologies - I'd forgotten that the junction still had its own 'box to the end : the Disused Stations website says "Selsdon Junction signal box was closed on 1st April 1984 and subsequently demolished and the oil siding finally closed in March 1993 and the junction with the Oxted line was severed but in 2008 most of the track to Croham Road is still in place." ............ what's more, my index says I took a photo showing it ! 

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5 hours ago, Wickham Green too said:

Apologies - I'd forgotten that the junction still had its own 'box to the end : the Disused Stations website says "Selsdon Junction signal box was closed on 1st April 1984 and subsequently demolished and the oil siding finally closed in March 1993 and the junction with the Oxted line was severed but in 2008 most of the track to Croham Road is still in place." ............ what's more, my index says I took a photo showing it ! 

The disused track serving the former oil terminal was retained as parts of the former Selsdon Goods Yd were designated as a Strategic Freight Site and the rail access would have been needed in the event of any traffic materialising.

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Were all the platforms at Bury Bolton Street electrified before services moved over to Bury Interchange? Different type of 3rd rail too being side-contact

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Before the North London line upgrade didn't Gospel Oak meet this criteria DC electrics from Broad Street and a single terminating platform for DMU's on the Goblin services.

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On 20/05/2020 at 09:31, Wickham Green too said:

Apologies - I'd forgotten that the junction still had its own 'box to the end : the Disused Stations website says "Selsdon Junction signal box was closed on 1st April 1984 and subsequently demolished and the oil siding finally closed in March 1993 and the junction with the Oxted line was severed but in 2008 most of the track to Croham Road is still in place." ............ what's more, my index says I took a photo showing it ! 

There's been photos and an article on the Croham Road track, disused platform and footbridge on various Facebook groups in the last few weeks.

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1 hour ago, MyRule1 said:

Before the North London line upgrade didn't Gospel Oak meet this criteria DC electrics from Broad Street and a single terminating platform for DMU's on the Goblin services.

 

The four track section of the North London Line from Dalston Junction to Camden Road consisted of the un-electrified  No1 or steam lines, which were still sometimes called that in the 1980's, and the DC electrified passenger lines.

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On 19/05/2020 at 21:22, Wickham Green too said:

Now, before you get to the next ( South Croydon ) 'box you come to the delights of Selsdon ( Junction ) which might fit the OP's bill !  The electrified Woodside and South Croydon veers off to the right with a single platform for a peak-hours only service and a back-shunt into the old goods yard for oil traffic while the 'main' Oxted Line passes between the remnants of its long-disused platforms and drops down to the aforementioned 'box and back onto third rail territory. It's not all MUs, of course, as there were a handful of Crompton-hauled business trains between East Grinstead & London Bridge.

 

Selsdon had two platforms in passenger service on the Elmers End branch right up till it shut - the Woodside to Selsdon line remaining double track till the end.

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16 hours ago, MyRule1 said:

Before the North London line upgrade didn't Gospel Oak meet this criteria DC electrics from Broad Street and a single terminating platform for DMU's on the Goblin services.

 

I would agree, and that reminds me of Barking, which (until the Goblin route was wired) had a non-electrified route; Not sure if the bay platform used was wired or not ? - Plus OLE on the LT&S and fourth-rail on the Underground lines.

 

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