N&W AC Signal System, Bannon - Columbus, 1911

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Attached article, from the 1912 Journal of the Railway Signal Association,
describes the N&W's new AC signal installation Bannon to Columbus in 1911,
using a coal-fired steam boiler at Dorney to drive two generators.


The important thing to realize about this installation is that it was a
VERY early installation of an AC signal system (AC track circuits, AC
semaphores.)  The first AC signal system in the nation was installed just
the year before (1910) on the Cumberland Valley RR between Hagerstown and
Harrisburg.


Before the advent of AC signaling,  signaling was done with "primary
batteries," made up in glass jars, using Copper + Zinc + acid.  Each such
cell of battery gave slightly more than 1 volt DC.  A set of these primary
battery cells was needed for each track circuit and each semaphore, and at
each "cut section" in each track circuit.  Interlockings needed vast banks
of batteries.  It was very expensive to make and maintain these batteries,
and they had to be renewed every few months when the chemicals were spent.


So AC signaling was a real revolution on the railroads.  The first problem
was, DC relays and DC semaphore signal motors would not work with AC, and
therefore all new equipment had to be invented to run on AC.  The second
problem was, there was no AC power commercially available outside of
cities, so the railroads built their own power houses to generate AC power,
and hung the transmission wires on their pole lines.  (Most railroads
transmitted their AC at 440 volts; the PRR transmitted theirs at an
incredible 6600 volts ! )


Perhaps some day we can assemble enough articles on this subject to gain a
comprehensive idea of what the N&W was doing signal-wise in the early
years.  Most of the information is out there in the trade journals - it
just has to be dug out and collated.


-- abram burnett


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