Tube electrification.

By and large london still has most of its victorian infrastructure. I suppose therefore that the earth leakage reason is still valid then. Also signalling concernes; making sure the running rail is properly bonded.

Then theres the earthing arguement. Having two live rails means that if one side gets earthed the other jumps up to full voltage so a service can still be run. Least I was told that ages ago; don't know if this is actually the case or not.

It wouldnt ghet rid of an obstruction in the middle either. If you look at Docklands, the ATO wire is in the middle presenting a partial obstruction. This would be the case with the tube in the future.

The IOWs electric infrastructure is nearing the end of its life; theres actually an argument for going 4 rail there.

I'd reckon that anyone at 55 Broadway who suggested this would be told it's not worth the expense, even as a big infrastructure project.

There would either have to be massive closures or two conversions - once to third or fourth rail, then again to third rail only once the rolling stock had all been replaced or modified. On top of that, you'd have to do all four subsurface lines (H&C, Circle, Met, District) simultaneously as well as enough of the Piccadilly (Rayners Lane-Uxbridge and South Acton-Barons Court) that you might as well do the entire line.

Personally, on the rolling stock I´d much rather have negi shoegear over earth brushes any day of the week.

The other big issue here would be EMC , once you start putting traction return current in to the same rails as the Track circuits you need to add much more serious filters on the train to avoid swamping the track circuit, so the line inductor and capacitor size will increase over those currently on the LUL trains which just adds weight for no really good reason.

The EMC study would cost an absolute arm and leg as well, I can just imagine all of the consultants rubbing their hands in lee if this was ever proposed

The Southern network is third rail, and by 1933 it already reached Brighton and Guildford, so converting it would have been a major undertaking.

(incidentally, in checking the date, I discovered that Wikipedia thinks that the Underground's 4th rail system is a legacy of the pioneer CSLR! You and I know, of course, that the CSLR did not adopt the four-rail system until 1924, ten years after it joined the UERL Combine. This left the Central (and, after the Met joined LT in 1933, the Northern City) as the only lines left not using the 4-rail system, which they finally adopted in 1940 and 1939 respectively.
The W&C was converted to 4-rail shortly before becoming an LT line.

Am I not correct that LUL trains are perfectly happy to work on conventional 3rd rail electrification systems, provided that some arrangement is made to get the negative shoe connected to the neutral runing rails. This can be either by laying a supplementary 4th rail, as on Putney to Wimbledon (or on any other section shared by LUL and BR 3rd rail trains), which unlike on the Underground proper has no direct electrical function but just provides a neutral route, being connected to the running rails. Alternatively the Isle of Wight approach can be to just connect the negative shoe to the wheels in some manner to provide a return path.

As long as the potential difference is 630v it doesn't matter to the train whether this is achieved by +420/-210 in the supply, or +630/neutral.

I believe I am also correct that the whole of the LMS Euston to Watford/Broad Street to Richmond etc network was 4th rail from being laid in the 1920s, up to some time around 1970, when the supply arrangements were changed to normal 3rd rail, and the central conductor rail removed from the parts not shared with the Underground, a change not particularly disruptive to achieve. So there is a precedent for such conversions.

Maybe someone with the technical knowledge can also explain to me (just because I'm interested) what electrical arrangements are needed at places like Putney, where trains pass from one system to another.

Well the CSLR had to wait till after the war and completion of the Central Ealing extension before it was integrated and then it was converted to 4th rail, had its tunnels enlarged, and joined to the Hampstead tube by new sections. The Central London was the exception to the rule, the NCL only joined with the Met in 1933 when the Combine as it was known became a public body, even more corporate than before.

Within 6 years the CL and NCL were converted and the NCL even had tube-sized trains running along it such was the level of standardisation.

If that was the approach of the LPTB (and its predecessor) then it is quite likely suburban lines would have followed suit when upgrades were done either as a cohesive London Suburban section of LT or part of a more integrated network. It is quite possible that the suburban network would have been standardised to 3rd rail as a cohesive unit which of course would include former LNER, LMS and GW lines. Either way, lines joined to the Underground would be converted to 4th rail.

Just to repeat because it doesn't seem to have registered, the government plan was not to incorporate the whole of the southern Railway 3rd rail system into the nascent organisation but to incorporate the suburban network of all 4 mainline companies whether electrified to 3rd rail, 4th rail or not electrified at all. Similarly there was no plan to incorporate 3rd rail services beyond the suburban area.

I would imagine the reason for BR converting the DC network to 3rd rail operation was in order to standardise the network, just as LT has always sought to do.

There are indeed neutral sections where the DR meets the BR systems. As the BR network uses the running rails for the return current, they too need to insulated from the LT rails.

On the BR 4-rail sections, the centre rail is bonded to a running rail. I believe the same applies on the Watford DC section from Queens Park.

ISTR the Richmond-Broad Street was similarly wired with the 4th rail bonded to the running rail and was there just because of the through running.

You may remember Sarah Siddons used to work specials on the SR; I gather it was a simple job to convert her to run on 3 rails by lifting the neggy shoes and bonding from there to the chassis! In the early 1970's, Bigal and myself proposed running an R stock tour to Portsmouth or somewhere like that on the southern. As R stock had lifteable neggy shoe gear, it would have been an easy change-over from 4 to 3 rail operation, but it never got much beyond the discussion stage.

On LU, I believe the diffference in potential is that the positive rail is +325v above neutral, the negative rail is -325v belove neutral to give the required 650 volts; on BR, the positive rail is +750v, running rails 0 volts!

I'm not THAT technically minded, but that was the simple explanation given to us as train crews.

I'm not aware of any plans to convert the IoW system to 4 rails. In my view, the expense would not be justified as all the signalling would have to be altered too. If done, it would mean any future stock would not be able to be tested pre-delivery on the main line! More missed phot opportunities.

There was a bit of a "crackpot" plan by the late Fred Ward and others to import used trams from Germany and run them on the Island in the 1990's as trams were being sold off very cheaply. but, like a lot of Fred's plans they came to nothing. Maybe someone should write a book about Fred!

Apart from 'Sarah', former Standard Stock used in the then TRC was also converted to run on 3rd rail only when lent to BR. There is a shot in an old Underground News of the TRC at Wimbledon, having been towed there by a battery loco. It was then taken into Wimbledon Depot.

What I understood him to convey was "the NCL only joined (the Underground), with the Met, in 1933" i.e. the NCL was not part of the Combine until its owner, the Met, joined it in 1933.

mikebuzz said "
Within 6 years [of creation of London Transport in 1933] the CL and NCL were converted and the NCL even had tube-sized trains running along it such was the level of standardisation."

All three lines even used "Standard" stock after conversion!

I think the more significant factor in the date of conversion in all three cases was that the original rolling stock was life-expired, at over 35 years old, and that, in the case of the CSLR, it was to be joined to the Hampstead Tube, and in the other two, Standard stock was available to replace the original stock, as the new 1938 stock came on stream elsewhere. (Incidentally, why did the Central get cascaded Standard stock instead of new 1938 stock?)

Note that the UERL did build some stock with non-standard current collecton: the Central's Ealing extension was opened in 1920, and new stock suitable for open-air running was built for it.