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Vice Presidents: Richard Hardy; Sir William McAlpine Bt, FRSE, FCIT, FRSA




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Great Northern Suburban Electrification and Signalling

Paul Hepworth

  12 October 2009

Thirteen members and guests were present on 12th October when Paul Hepworth visited us to present his personal recollections of the electrification and associated resignalling of the Great Northern suburban lines out of Kings Cross during the late 1970s. Paul started his career in BR, before moving on, during the privatisation years, to various signalling companies including Westinghouse, finally retiring in 2007

Paul started his presentation with a short powerpoint display comparing the original GN route diagram and the post electrification route, highlighting the restructuring of the Highbury and Islington to Moorgate route. Overall, the GN suburban routes from London to Royston and Huntingdon included some 50+ mechanical signal boxes and three power boxes.

The second oldest power box was at Potters Bar, installed as part of the 1950s rebuild. As part of the this earlier modernisation phase, New Barnet and Hertford North had been resignalled with non-standard (non-AC immune) signals. For the electrification upgrade, local electronic interlocking centres were installed at the major junctions, which after a period of testing were relocated into the old mechanical box. This started at Hertford North and provided new signalling on the Hertford branch allowing diversion of trains from the main-line. Each weekend, one of the temporary local interlocking in one of the old signal boxes was transferred to Kings Cross and the then the redundant local interlocking was transferred back to the local relay room, which reverted to emergency use only. Meanwhile a temporary control was set up for Kings Cross station, which communicated originally with the local mechanical boxes but ultimately to the new power centre for the whole GN line – coincidentally located in the same power box!

Paul then moved to a slide show of the before and after locations, starting at Farringdon with an old class 33 with slam-door, short length carriages (necessary to get round the “hotel curve” at Kings Cross). Then to the old Kings Cross underground widened-line station, and Kings Cross suburban platform 14 which could only just accommodate a 6 coach train. At the other side of the station was York Road station with its connection to the Widened Lines. This included a link one to the west although, as there was not an equivalent one on the other side of the station, you could only send trains towards Paddington and they had no way to get back (Perhaps a way for the GWR to take over the world?).

We then looked at the demolition of the old signal box at Kings Cross, and, in the background with the change-over in place, the outer suburban trains were being temporarily replaced by non-lavatory-fitted old Widened-Line stock. Some of the Kings Cross platforms were dug up to allow their extension, meaning that signal cabinets had to be temporarily supported. As a side comment, Paul noted that one of the route indicator on the slow line tunnel was recently damaged by the Hogwart's Express because of the over-sized Olton Hall cylinders.

Moving to Finsbury Park, we look inside each of the old mechanical boxes. The first look over the bridge to the Cannonbury line with a view of Ashburton Grove box. The latter had its original GNR track diagram until it finally closed in the remodelling. Finsbury Park No 1 box on the Cannonbury line was by the side and overlooking Drayton Park. At Finsbury Park No 2, Paul remembered an incident when he was working on the resignalling and temporarily put two nuts on a running line while he made some modifications. They were quickly converted to cauliflower washers by a passing train! Finsbury Park No3 still had gas lighting burners until the end, while No 4 was in the way of the new dive-under onto the Moorgate line, so was an early casualty. One of the unusual features at Finsbury Park station was that the up Moorgate line had a test signal to show if the LT trip cocks were operating. The signal would not clear unless the trip cocks work. Finsbury Park Nos 5 and 6 were at the north end of the station and were the last to be replaced.

Harringay station box was unusual in controlling both up and down lines. Harringay west up box temporarily took over control of passenger lines during the upgrade. It was at the time of the upgrade that ground heave in the cutting beneath the nearby tower bock meant that new steel piling was needed, something which is still evident today.

Hornsey had 3 boxes which were replaced by a temporary interlocking on the up side to control the area.

At Wood Green (where Paul met his wife in the adjoining pub) a scissors crossing on the down side was removed meaning that trains could no longer switch between the main and Hartford Loop – needless to say, on the first day, two trains arrived at Wood Green on the wrong platforms. Wood Green No 4, right next to the main line, was the temporary interlocking centre. It shook violently when trains passed, and an earlier generation of signalmen had replaced the standard railway clock with a ship's clock as it managed to keep time despite all the rocking.

The new control panel at Gordon Hill originally oversaw a number of the ground frames for sidings which were used to store spare stock – these have since been removed. Hertford North controlled the rest of the loop to Langley Junction.

At Woolmer Green box there was no mains water, so the re-signalling team learnt never to ask for a cup of tea as the signalman only had canned supplies delivered once a day. At Welwyn Garden City a new flyover was built. The old mechanical box housed the local control covering the area from Welwyn North to Hatfield.

The team finished the resignalling on the Hitchin to Sandy route, the latter being the limit of the Kings Cross signalling scheme.

In questions, Paul noted that trains were not stopped running during the resignalling and there was no bus replacement. Also the local interlocking is still there which is a god-send these days when there is a communications problem. Indeed, the signalling on the route remains the same, apart from at Finsbury Park, which suffered wire degradation and has been replaced by a local digital system – which, surprisingly, operates slower than the 1970s version! The new “Platform 0” at Kings Cross will need some modifications to the signalling which will require some specialist expertise – Paul wishes them well!

Paul ended with a couple of anecdotes. It was well known that a “bush telegraph” operated between signalmen, its primary purpose being to keep track of the chief signalling inspector when he started his tour of inspection from GN House just outside Kings Cross. There was also the “overtime special”, a train from Stratford to Leeds carrying Bank of England notes and bullion which stopped at Finsbury Park station for a crew change. With armed police on-board there was never any delays in getting them on their way.