Why the power rails are where they are

Some of the more long-lasting decisions that impact on today’s railway system are the result of complete accident. The following tale is an example where railways, having decided to do one thing then do another. It is also an example of poor communication and lack of understanding of the consequences of decision-making, or even that a decision has been made. I signed off last time with the question ‘it couldn’t happen now?’ and am minded to ask the question again!

Shortly after the twentieth century dawned, Britain was found to have a number of electrified railways in operation, with more on the way. Each had its own unique electrification system and current rail arrangement and it had become obvious that if any of the systems were to be enlarged then it would be conducive to the longer term interest if a common standard were adopted to facilitate through running. The railway companies got together and concluded that the optimal arrangement was for the positive rail to be located 19¼ inches outside the running rails. The measurement of conductor rail position is always made between the centre of the conductor rail and the gauge face of the nearest running rail. It seems to have been left open whether the return was to be via the running rails or a separate centrally positioned negative rail, but that is not important just here. Most of the railways agreed to this arrangement in 1903 though there were a few dissidents. The LSWR was one dissident and apparently preferred a 15-inch location for reasons considered peculiar to its own system; it isn’t clear which of the two they would have gone with if left to its own devices.

The Metropolitan Railway had been a party to these discussions and concurred with the 19¼-inch arrangement. It began planning its underground line electrification accordingly, on the assumption that this was what today would be called ‘the standard’ and the District would follow it.

The Metropolitan, with the District, had worked together on a joint electrification trial at Earls Court in 1900; this was equipped with dual outside current rails at a 12¼-inch distance, one rail was positive and the other negative. Two conductor rails were considered essential here, as the running rails were not bonded and it was easier to install a temporary system that way. As was common at the time, the conductor rails were of ‘channel’ section, a design the District soon took a dislike to. When the opportunity arose to install a larger-scale trial on the Ealing and South Harrow line in 1903 some improvements were made. First the rail section was much increased by avoiding the channel type rail and using a ‘vignoles’ design of much greater section which improved conductivity. Secondly the negative rail was moved to the centre allowing the positive rail to be installed either side of the running rails as was most convenient; the top of centre rail was 1½ inches above the running rail and facilitated the large conductor rail section as well as allowing the shoes to pass over the trackwork at points without making electrical contact. Thirdly, the position of the conductor rail was altered to 16-inches, about which more needs to be said shortly. Board of Trade approval was sought and granted for all this, the railway inspectors not giving much attention to the positive rail position on the basis this was only an experimental system. This is not, however, how Yerkes saw it; he took it that the Board’s railway inspectorate supported the 16-inch position. That two interpretations were possible was to become an issue.

For a while nothing more was said. The District was happy with the Ealing & South Harrow arrangements and late in 1903 began installing conductor rails to the same design in the Earls Court area. At this point the Metropolitan twigged that all was not well as they were about to begin installation at the 19¼-inch spacing, current rails and insulators actually being on site. Clearly the Inner Circle route could not be operated with one company’s trains of one type using an entirely incompatible electrification system belonging to the other company! In addition there was a significant joint section, now in an ambiguous position. One might infer from this that communication between these railways was not all that it should have been.

The Metropolitan appealed to the railway inspectors for guidance, the tone of the letter suggesting they were somewhat put out. They also had the Great Western pressing them for clarity because that company had to electrify the Hammersmith & City and were also expecting to install at 19¼ inches. This proved to be another example where the inspectors’ immediate response was to avoid being in the middle of a dispute where whatever decision they made might go horribly wrong, a position accentuated by the Metropolitan’s suggestion that the Board had supported the use of the non-standard arrangement in the first place, and not told anyone.

Yerkes was hurriedly consulted and he produced a reply that demonstrated fait accompli. Yerkes explained that in addition to electrifying the District he was constructing three tube railways, one of which he had acquired half-built from the failed London & Globe finance corporation, previously run by financier Whittaker Wright who had embezzled a great deal of money and was convicted of fraud before taking poison and killing himself. The tunnel had an internal diameter of only 11ft 8¼ins and Yerkes’ desire to utilize a 4-rail system presented a problem in finding a suitable location for the outside rail (I suspect these early tubes when conceived had contemplated using just three rails). After a great deal of thought it was found that by using a smaller, almost square section rail with upper surface mounted 3 inches above the running rails it was possible to locate it 16 inches from the running rail, but no more (nor could the extra height be less than 3 inches without excessively reducing rail section). The other tubes would have to be built the same way. It was quite impossible to space the conductor rail at 19¼ inches.

Yerkes explained that he wanted the tube stock to be able to inter-run with the District, both to Mill Hill Park and to and from the car sheds at Lillie Bridge which would be used jointly. This could only be achieved if the District also adopted the 16-inch spacing. Discussions had taken place with the London & South Western Railway, over whose lines the District had significant running powers, and they had agreed to the use of 16 inches instead of their preferred 15 inches, even though it would mean their own trains would have to follow suite when they electrified their own system (they didn’t actually run their own electrics until October 1915). In addition the Ealing & South Harrow was already equipped at 16 inches which had been entirely satisfactory (and approved by the Board of Trade) and the District didn’t want the inconvenience of altering it. They saw no problem in London using one spacing with the northern areas using the 19¼-inch spacing as interworking between these areas seemed unlikely; however Yerkes could see no good reason for those companies not to adopt 16 inches as well.

The inspectors were keen that there be one standard (except perhaps for deep tubes) and sought the views of the Railway Companies’ Association in November 1903, though informally it appeared they would be prepared to accept the 16-inch arrangement, a matter that annoyed the Metropolitan when they found out. The Metropolitan wrote a slightly irritated letter to the Board in December saying that the District’s Sir Robert Perks had told them they were expecting the 16-inch system to be endorsed and, desperate to make progress, the Metropolitan had also begun laying at that spacing. They wondered if the Board would be good enough to tell them officially as endorsement of any other arrangement would be hugely disruptive. The Board of Trade’s railway chief, Sir Herbert Jekyll, was relieved that events had moved on so far that it was no longer necessary for the inspectors to stay in the firing line and replied to the Met just before Christmas ‘that there was no good reason’ not to continue laying at the 16-inch spacing, which became the de factostandard in the London area, later being followed by the London, Tilbury & Southend (later Midland Railway) and London & North Western lines which would both share tracks with the Underground’s trains. And so it happened that the main lines were compelled to use the 16-inch spacing having only just agreed to use something wider; and so it still is today.

Incidentally, Yerkes was by no means wedded to the 4-rail system and was, of course, already familiar with the American electric railroads which generally used only three rails. He explained that at such time when it was possible to replace the District’s running rails with a much heavier section, then bonding them together might provide an entirely satisfactory return path in which case the negative rail could be removed. In the event this was never done, though the very similar Central London was happy to use a 3-rail system with automatic signalling until the late 1930s.
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About machorne

I have always lived in London and taken a great interest in its history and ongoing development. This extended into the history of its transport services, about which I have written a number of books - I have spent most of my working life working in the industry and observing changes from within, mostly to the good, but not always so. I continue to write, and have a website with half finished stuff in it so that it is at least available, if not complete. Several new books are in hand. I have many 'works in progress' and some of these can be found on my website; the we address is http://www.metadyne.co.uk
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