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Special switch at Elsenham

British signalling of the past (UK, excepting Northern Ireland)

Special switch at Elsenham

Unread postby John Hinson » Mon Oct 30, 2017 12:19 pm

Another interesting piece of equipment, at Elsenham:
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Photo: N L Cadge 14/8/80.

I am guessing this has something to do with mixed Absolute Block/Track Circuit Block according to whether Newport is switched in although most boxes with mixcd working I have seen had no such equivalent. It looks like an ex-GNR block (or telegraph?) instrument but another, more general, view of the box shows it to have no apparent trigger or other external latching device.

I'm not sure if that is a push-button or lamp mounted on the left of the instrument.

On the right is a small shelf-mounted lever lettered "EMERGENCY SWITCH" - I wonder what that does. It could be a replacement for the auto signal in mid-section, I suppose. There was a slide at Wendover that did the same.

All thoughts welcome.

John
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Re: Special switch at Elsenham

Unread postby ge.signals » Mon Oct 30, 2017 4:33 pm

John,

Re the mysterious 'pegger', I'll pass it on to Barry Bridges who was a signalman at Elsenham. The lever switch to the right was indeed the emergency replacement for the North Hall auto - an electrically-operated mechanical colour-light signal.

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Re: Special switch at Elsenham

Unread postby Richard Pike » Mon Oct 30, 2017 10:11 pm

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Re: Special switch at Elsenham

Unread postby BHornsey » Mon Oct 30, 2017 10:28 pm

Evening John.
I recognise the emergency switch; it was the Emergency Replacement for North Hall Up Auto signal. It was still there when I worked Elsenham (just before it closed).
I have no memory of that block switch though. By the time I worked Elseham, the signalbox at Newport had been closed and relocated as a block post on the up platform so it may have been something to do with the old Newport Box arrangements.
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Re: Special switch at Elsenham

Unread postby Richard Pike » Wed Nov 1, 2017 2:56 pm

Elsenham is shown as being at 35m 49c in my 1978 Sectional Appendix with Ugley LC at 37m 13ch, Newport at 39m 69ch, Audley End at 41m 48ch and Great Chesterford at 45m 56ch. From as far as i can make out if Audley End box switched out the Elsenham - Newport section became Absolute Block. The linewire currents required to operate the block control relays between Elsenham and Newport would be nowhere near enough to operate the same at Great Chesterford if Newport also switched out. Conversely if a sufficient battery was provided at Elsenham to operate the block control relays at Great Chesterford it would perhaps overpower the same relays at Newport. Add to that the block dials and any level crossing repeaters plus any block dials that may have stayed in circuit then an increment switch may have been the answer. What does strike me is the complexity of the increment switch. I wonder if the were additional controls applied to it's use? There would have been a relay that knew when the track circuits were clear when the section was being operated in TCB. I wonder if there was additional circuits via Audley End and Newport block closing switches that enforced the Elsenham increment switch to be operated before a Line Clear could be given?

Where was North Hall auto signal? Didd it protect Ugley level crossing?

Elsenham..

https://www.flickr.com/photos/pwayowen/22645857530/

Audley End..

https://www.flickr.com/photos/pwayowen/18114263759/

We have nothing for Newport i'm afraid.
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Re: Special switch at Elsenham

Unread postby ge.signals » Wed Nov 1, 2017 3:07 pm

In order to understand the purpose of the ‘Newport Switch’ in Elsenham signal box it is necessary to examine how Elsenham interfaced with the neighbouring signal box at Newport to the North.
In 1932 North Hall signal box, between Elsenham and Newport, was abolished and replaced by automatic colour-light Intermediate Block (IB) Home and Distant signals on both Up and Down lines. The automatic operation of these IB signals required both lines between Elsenham and Newport to be fully track-circuited making it possible for both Up and Down lines between Elsenham and Newport to be worked by Track Circuit Block (TCB). Newport could be switched out when not required, leaving the section North of Elsenham as Elsenham – Audley End. However Newport – Audley End retained Absolute Block working after the 1932 alterations, and thus with Newport switched out, it was necessary for Elsenham to have block instruments for communicating with Audley End, but only when Newport was closed. This resulted in the provision of a special switch on the block shelf at Elsenham, the purpose of which was to bring the block instruments for the Elsenham - Audley End into operation when Newport was switched out. This switch had to be operated in conjunction with the switching out of Newport box, but exactly how, and why it took the form of a ‘pegging’ instrument with a blanked-out display, isn’t now known. A further complication was that both Newport and Audley End signal boxes were sometimes switched out, leaving the section to the North of Elsenham as Elsenham – Great Chesterford, but as Audley End – Great Chesterford was worked on the Absolute Block principle it made little difference apart from having an exceedingly long section.
Finally to the right of the ‘Newport Switch’ is a miniature lever serving the function of an Emergency Replacement Switch for the Up automatic colour-light IB Home Signal between Newport and Elsenham. Interestingly, this was also used to hold the Up IB signal at Danger when slow, unfitted freights were approaching Elsenham whilst the signalman there was ‘waiting for the road’ through to Stansted in order to prevent any minor rolling-back from causing derailments on the catch points which existed on the Up line between Newport and Elsenham.
Thanks to Barry Bridges and Andrew Wallis for their assistance in the preparation of this note.
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Re: Special switch at Elsenham

Unread postby John Hinson » Wed Nov 1, 2017 3:54 pm

Thank you.

Yes, I was aware of the relationship with the mixed block working according to Newport's status but as I said equivalent boxes elsewhere didn't have such. It is (was) a telegraph instrument and not a pegger, by the way. Any pegging must be achieved electrically inside the case, there is no latch of any sort externally.

The purpose of that little lever is interesting - the slide at Wendover I mentioned served a similar purpose but I would need to re-read the local instructions to see the reason. There certainly were some catch points nearby!

Many thanks again.

John
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Re: Special switch at Elsenham

Unread postby Richard Pike » Wed Nov 1, 2017 5:54 pm

I have never evidence seen anything similar on the GN. I have circuit diagrams for a few boxes but nothing is shown. The little lever is more exciting.

I have recently acquired what was Great Chesterford up main intermediate block auto distant. (Was this the last mechanical searchlight in use?) As it may well have it's lenses missing i'm free to convert it to a stop signal. If thing's turn out that way i'll have to find it a job as an auto stop and it appears i have the right thing to use as a replacement switch.
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Re: Special switch at Elsenham

Unread postby JRB » Wed Nov 1, 2017 10:44 pm

On the [G]WR, with long sections with block switches, all peggers had enough battery power to reach the far end and intermediate boxes had resistors in the non pegger circuits to compensate. The block switching drawings had comprehensive details to take account of line wire/cable resistance, BCRs, peggers using a common box supply &c. It still had to be finalised by trial and error.
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Re: Special switch at Elsenham

Unread postby John Hinson » Thu Nov 2, 2017 3:16 am

JRB wrote:On the [G]WR, with long sections with block switches, all peggers had enough battery power to reach the far end and intermediate boxes had resistors in the non pegger circuits to compensate. The block switching drawings had comprehensive details to take account of line wire/cable resistance, BCRs, peggers using a common box supply &c. It still had to be finalised by trial and error.

I don't think this has anything to do with line resistance - it would appear to be solely to do with the change from Track Circuit Block to Absolute Block when Newport was switched out. I am no expert on electrical circuitry but I would assume the "normal" arrangement would be for the closing switch to activate the circuitry to activate the block instruments, Line Clear releases etc. For some reason it seems to have beendone separately here, but similar circuitry would still be required to lock/unlock that instrument so I cannot figure out the benefits. We shall probably never know why.

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Re: Special switch at Elsenham

Unread postby JRB » Thu Nov 2, 2017 8:42 am

I don't know about the special circumstances there, but any switching with big differences in distance for 'IN' and 'OUT' required a lot of drawing office work.
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Re: Special switch at Elsenham

Unread postby BHornsey » Thu Nov 2, 2017 8:48 am

When I was at Elsenham, that block switch had been removed. The same arrangements (TCB with Newport in, AB with Newport out) still applied and, if I remember from my one visit to Newport, the block switch was at Newport.
Mind you, my memories were that TCB applied on the Up only, Newport - Elsenham - Stansted. AB applied on the Down. My 1964 Sectional Appdx shows TCB both ways however so I assume changes were made when everything was rationalised, or when Newport SB was demolished and relocated to the Down Platform.
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Re: Special switch at Elsenham

Unread postby RDNA » Thu Nov 2, 2017 9:07 am

John Hinson wrote:.................... We shall probably never know why.

John


John, the post by 'ge.signals' gives a pretty comprehensive explanation apparently sourced from someone who worked the box.

However I have an observation - the BR standard block instrument on the left is labelled 'Newport', implying that it worked to Newport when it was open.

I suggest that since the arrangement with the "Auto IB" dates from the 1930s, long before the TCB regulations that I am familiar with were laid down, then the method of working between Elsenham and Newport could have been similar to that between Hellifield South Junction and Bell Busk.

I also suggest that the right hand instrument labelled 'Newport' 'IN/OUT' could have been improvised to activate 'Tail Lamp Reminder' circuitry when Newport was closed.

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Re: Special switch at Elsenham

Unread postby John Hinson » Thu Nov 2, 2017 10:41 am

BHornsey wrote:When I was at Elsenham, that block switch had been removed. The same arrangements (TCB with Newport in, AB with Newport out) still applied and, if I remember from my one visit to Newport, the block switch was at Newport.
Mind you, my memories were that TCB applied on the Up only, Newport - Elsenham - Stansted. AB applied on the Down. My 1964 Sectional Appdx shows TCB both ways however so I assume changes were made when everything was rationalised, or when Newport SB was demolished and relocated to the Down Platform.

Thanks, Brian, that's interesting. I can confirm from a photograph of the diagram on the same date as the photo above that TCB existed on both lines at that date.

RDNA wrote:
John Hinson wrote:.................... We shall probably never know why.

John


John, the post by 'ge.signals' gives a pretty comprehensive explanation apparently sourced from someone who worked the box.

However I have an observation - the BR standard block instrument on the left is labelled 'Newport', implying that it worked to Newport when it was open.

I suggest that since the arrangement with the "Auto IB" dates from the 1930s, long before the TCB regulations that I am familiar with were laid down, then the method of working between Elsenham and Newport could have been similar to that between Hellifield South Junction and Bell Busk.

I also suggest that the right hand instrument labelled 'Newport' 'IN/OUT' could have been improvised to activate 'Tail Lamp Reminder' circuitry when Newport was closed.

DB

Thanks but you misunderstand me. I am well aware of its purpose and stated that in my earlier posts before said explanation was given. It is "why" such a device was necessary when not elsewhere that I was referring to in the "probably never know" department.

The block instrument is labelled Newport because the bell is used to describe trains to/from Newport.

The LNER Automatic Signalling was very similar to what we call TCB today, the most significant difference was that a track circuit was not normally indicated in rear of the first (only, in this case) automatic signal. The one under discussion was indeed an Automatic Signal (and was plated as such) according to the diagram and should not be confused with IB signals. The LNER arrangement led to the curious possibility of a driver telephoning from a red signal but not indicated in the box. There's nothing dangerous about this of course, and many such installations lasted into recent years. The working between Hellifield and Bell Busk was not comparable to the LNER's system.

I am not sure I accept the explanation of the little lever being to avoid roll-backs onto the catch points. Those catch points were within the overlap of the auto! The catch points in rear of the Auto are actually inside its distant so much closer. I have checked the arrangements at Wendover (which was another LNER installation of a similar era) and that control was for fog working as the Up Distant was semaphore. Now the same situation existed at Elsenham until the 1950s so my guess is that the lever was provided for that purpose but had no real function after the distant was made colour-light.

Best regards,

John
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Re: Special switch at Elsenham

Unread postby ge.signals » Thu Nov 2, 2017 4:44 pm

A minor correction to my earlier post: the date was 1927 and not 1923 as I was advised. I have the MT29 for the North Hall 'Autos' dated 15th July 1927. If only we had copies of the Instructions for switching Newport Out and In!

I'm also interested in the history of this as surely in 1927 AB would have been with Tyer 2-position blocks, and I wonder if they had to be changed at that time for LNER 3-postion blocks. Does anyone have interior photos of Gt Chesterford, Audley End, Newport or Elsenham before the BR 'standard' blocks replaced what was there previously?

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