electrified location

[NW Mailing List]

We're the signal controls interlocked with the switch controls so that a signal could never give an indication that was incompatible with a physical switch position?

Bob Bayles

Sent from my iPhone

> On Jan 16, 2017, at 09:49, NW Mailing List <nw-mailing-list at nwhs.org> wrote:
> 
> Jim,
> 
> I can't help you with a location for that photograph, as I never worked "under wire" on the N&W and never worked on the Pocahontas Division.  But I will comment on two other items you asked about.
> 
> 1.  From what I recall about the N&W, the "S" on the signal number plate identified the least favorable indication of the signal as being Stop & Stay, rather than Stop & Proceed.  My guess would be that the N&W did not begin applying "S" plates to signals until the introduction of Centralized Traffic Control.  
> 
> 2.  The "L" designator following the signal number indicates something that operating crews did not have to know (and probably never knew,) namely that the lever governing it was to the "Left" on the control machine (whether that was in a tower or on a Train Dispatcher's control machine.)  The commensurate designation, of course, was "R" for "Right."
> 
> In the days of the old "armstrong" (i.e. Saxby & Farmer type) interlocking machines, levers were (to use a modern, trendy term) "binary."  That is, they had only two positions:  In or Out.   Any lever shoved back in the lever frame was in "Normal" position; any lever pulled out was in "Reverse" position.  Because levers had only two positions, a lever used to control a signal could ONLY control ONE signal.
> 
> However, when the EP (electro-pneumatic") interlocking machines were introduced (around 1910,)  the levers for signals were designed with THREE positions,  giving an economy in the number of levers needed on the machine.  A single lever could then control the display of  TWO  signals.  In almost all cases, the two signals controlled were opposing signals on the same track, say for instance, the eastbound and westbound home signals on No. 1 track at an interlocking.  
> 
> At this point, it became necessary to add direction of traffic to the nomenclature, for the sake of clarity.  "L" and "R" were the designators chosen, for Left and Right.  But what was "Left,"  and what was "Right"?    Those terms were keyed to the direction of movement with respect to the model board in the tower, and how the leverman faced the machine and/or model board.   Obviously, the R and L directions would be reversed for towers located on the north or south sides of the main line.
> 
> The three positions for signal levers on EP machines were:  (a) lever hanging straight down = signal at Stop;   (b) lever right = signal for movement to the Right displayed;  (c) lever left -= signal for movement to the Left displayed.  (By contrast, levers controlling switches have only two positions:  Normal or Reverse.   Switches, and their controlling levers, are "binary: :  there is no middle position between Normal and Reverse.)
> 
> When Central Traffic Control machine were introduced, the R and L designators were retained.  CTC levers were manufactured with two different types of detents cut into the cams:  Switch levers had two detents;  Signal levers had three.  
> 
> This is about the best I can do for you, Jim.   The Older and Wiser heads will obviously know more about these topics.
> 
> History, again, is the key to understanding everything.
> 
> -- abram burnett
> 
> from the amish turnip patch on pennsyl-tucky
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