Fixed Ground Signal versus Limit of Shunt sign

[Benhar Jnc]

Looking at an old Signal Box diagram, I noted one ground signal was fixed at danger and wondered why a 'lower cost' installation of a Limit of Shunt sign might not have sufficed. As every day is a school day, I wondered what the deciding factors might be?

[davidwoodcock]

Could the ground signal have originally been workable, in which case just fixing it "on" when requirements changed would have been cheaper than providing a Limit of Shunt sign?

The LBSCR went the other way and had some workable Limit of Shunt signs!

[JRB]

Was the fixed ground signal at a normal 'Limit if Shunt' site?

[Benhar Jnc]

The fixed ground signal was on what looks like a goods loop line (BR Sc Region) - looks as though it was simply positioned to limit long shunts back along the loop from an adjacent yard. I'm unaware if it was ever operational. May have been to indicate the boundary of acceptable bi-directional working? I haven't come across many examples of a fixed ground signal on BR metals, on the other hand I've seen many a Limit of Shunt indicator.

[John Hinson]

I think generally a fixed shunt signal is the residue of rationalisation whereas a LoS board will have been designed into a layout. If you could tell us the location where you have seen this, I might be able to look at the place's history for clues.

The only situation that demands a fixed signal in preference to an LoS board is where the signal reading to it gives a main aspect.

Of course in modern signalling there is very little difference between a shunt signal and an LoS indicator - both display two small red lights and it is only the inability to show an off indication that separates them.

John

[Benhar Jnc]

Thank you Mr Hinson. The location I was referring to is Haymarket Central (Edinburgh) in its latter years and the fixed ground signal appeared to be located on a goods loop line connecting Haymarket MPD with the Goods Yard at Haymarket railway station. Possibly it would have stopped shunting moves out of the goods yard fouling up loco movements at the MPD and disrupting the timetable?

Trust adding a specific location helps. Interested to understand if there were many other examples of fixed ground signals around the network?

[John Hinson]

The author of the drawing you have been looking at has kindly sent me a copy, and that is a very interesting circumstance indeed.

It is a quite late version of the layout, after the diesel depot came into use, and I had not seen that diagram before. However, I do have a 1929 version which compares rather interestingly. I have posted it at:
https://signalbox.org/diagrams.php?id=1176

Although there is a large gap between the dates, the ingoing signal was a fixed flap-disc so this is definitely a historical arrangement rather than the result of rationalisation. There probably wasn't such a thing as a Limit of Shunt Board in the days when that signalling was put in. As I see it, it allows the straight route from the sidings to be used as a shunting neck without allowing such shunts to enter the shed.

But it begs the question of how locomotives actually entered the shed. Was there perhaps authority given somewhere for engines to be called past the fixed signal by shed staff? By the later plan (which is dated 1971) it is possible that all locos entered the shed via the secondary route not there in 1929.

Yet there is also a fixed disc preventing departure by that secondary route. That is not "historical" and its purpose is also worth thinking about. If this is to prevent moves in the depot going beyond it (should we suppose all shed departures were via signal 1 (3/4/6 in 1929)?) then surely a Limit of Shunt board should rightfully have been provided there. Perhaps a look at local instructions would enlighten us.

Whilst I can think of a few places around the country where a fixed disc survived to act as an LoS after rationalisation, the arrangements you have introduced us to are certainly rare. They have a historical background, but it is remarkable such were still applicable in the 1970s.

Best regards,

John

[Benhar Jnc]

Thanks for opening up the discussion beyond a generic question. The 1929 drawing that you have kindly posted now confirms that a fixed ground signal was in place at that rather busy location for over 50 years - so it must have been well known to a lot of loco crews from far and wide. It will be interesting to see if any forum members with local knowledge can enlighten us further regarding this rather rare signalling arrangement.

[davidwoodcock]

Can I suggest, given its location, that it was more akin to the modern "STOP - AWAIT INSTRUCTIONS" board - which I suspect might be found at the entry to quite a few depots.

[John Hinson]

Herewith now is the 1970 layout, for which I now have permission to reproduce here:
https://signalbox.org/diagrams.php?id=1177

This will certainly make the subject clearer to those reading this thread.

With many thanks to Robert,

John

[Benhar Jnc]

For the purposes of keeping our conversations clear - worth noting that Robert's diagram contains 2 fixed ground signals and they are very close to each other.

[alancolq]

Hello all,

I used to visit the Haymarket boxes in the early 1970s, until they closed in December 1975. From memory - and I am not 100% sure of this - light engine movements into and out of Haymarket shed were separated so that movements out of the shed were never permitted via points 8, hence the fixed disc protecting them.

While I'm on, I note a small omission on the later of the two diagrams: disc 85 is missing. It was used quite often for reversing from the Up South Main, back through 84 points and into the sheds. I never recall seeing the reverse of this - locos departing the sheds and crossing to the Up South to head towards Waverley, but presumably this happened too from time to time and was signalled by the lower of the selected discs No1, and by disc 10 from the North Loop.

Thanks for posting the older diagram - I had been curious about that since seeing various old photos!
Alan

[Corrour]

Thanks for spotting that omission Alan, I'll amend accordingly and ask John to re-post.

Robert

[alancolq]

My pleasure Robert,

Your diagram is incredibly realistic: I only remembered 85 from lending my unofficial hand at that end of the frame a few times when "wheeching an engine across", as one of the regulars used to say!

Alan

[StevieG]

Presumably the left - most No.7 points, close to one of the fixed discs and 37 / 44 signals are those referred to in this thread as No.8 ?