utility pole question- additional info

Fri May 5 15:58:26 EDT 2023

One additional bit of info about the utility poles:  The white insulators carried the dispatcher’s phone;  the clear insulators carried the CTC signal.

Bill Mason

William M (Bill) Mason 

 <mailto:wmmason at verizon.net> wmmason at verizon.net

From: NW Mailing List [mailto:nw-mailing-list at nwhs.org] 
Sent: Friday, May 5, 2023 12:36 PM
To: NW Mailing List
Subject: Re: utility pole question

Thanks for the great info, Abram.  I am just trying to model this accurately.  Understanding it somewhat makes it easier to do, especially in places where photos are not available.

Mike Rector

On Thu, May 4, 2023 at 10:53 PM NW Mailing List <nw-mailing-list at nwhs.org> wrote:

I forgot to address Herr Rektor's questions about the strange-looking brackets on the pole itself and on the bottom cross arm. 

Those are transposition brackets, known in the vernacular as "tramps." 

The only place you will see them on railroad pole line is where voice circuits (i.e. teleghone circuits) are present on the pole line. 

The purpose of the brackets is to transpose the position of the two wires carrying a telephone circuit.  (Remember, I told you that telegraph circuits operate with only one wire, but telephone ckts use two wires.)  If the position of the wires were not shifted periodically, the quality of the voice transmission would degrade very quickly. 

In the 1830s, Joseph Henry discovered that a current moving in one wire will induce a current in another wire in close proximity.  This is called electrical "induction."  The way to keep induction from reaching objectionable levels on pole line is to transpose the relative positions of the two wires at certain intervals.  The distance between tramps seemed to vary from road to road.  The PRR tramped a telephone pair every 5000 feet.  It seems that the N&W's tramps were much closer together than 5000 feet. 

Another thing which has been largely forgotten is the significance of white porcelain insulators on pole line.  They were used on every other cross arm to mark the Train Dispatcher's telephone circuit wires.  This was done so that the Section Foreman (or others) needing to talk to the Train Dispatcher could identify the pair of wires which carried his voice circuit, and could clip their portable telephone onto the pair.  There was no identification of circuits by white insulators prior to the advent of the telephone in Train Dispatching work.  The telephone was introduced into Train Dispatching in 1909 on the Radford Division.  See attached PDF from Telegraph Age, October 16, 1909. 

Induction also affects metallic wiring in the computer world.  Some time peel the insulation off a chunk of Cat-5 or Cat-6 communication cable used for the wiring of offices, and you will see how the pairs have been twisted and then rotated periodically as the cable was wound.  That is to cancel the effects of electromagnetic induction. 

If you wish to inform yourself on this topic, I suggest the biography of William Henry, published under the title Joseph Henry, His Life and Work, by Thomas Coulson of the Franklin Institute, publ. Princeton University Press, 1950.  There are plenty of copies available at the on-line used book stores. 

-- abram burnett 

Laser-Guided Designer Turnips 

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