[PRCo] Re: Ground currents

[Fred Schneider]

Nice simple treatise Russ.  Enjoyed reading it and learning something new today.  .
I recall a tale from Jim Shuman (it may have been published in Headlights) about Jim and Al Pitman and
Dave Cope and perhaps even Bad Man and Machine Gun Johnson, driving back to Philly after a fantrip on the
Southern New York Railway in 1938.  From the auto they were watching the SNY car returning to the barn at
Hartwick.  I think I remember Jim talking about a constant arcing at rail joints because so many of the
bonds had broken over time.  As long as the juice found some way to get home, they didn't care.

fws

Boris Cefer wrote:

> This is reply to my request regarding ground currents which I'v just received from Russell E. Jackson:
>
> With regard to your question below, here in the "wild west", things are not
> done with such great engineering and perfection.  It has always been
> typical to just use the rails for return currents.  Because rail joints may
> break, and to ensure there is minimum resistance in the return, paved track
> has typically had a "cross bond" connecting the rails about every 100 feet
> or so.  On open track that is not done.  Where very large currents are seen
> and one rail is used for the signal circuits, (typical of the NY subways),
> which results in only one rail being in the traction return, it is typical
> to add a negative cable to provide greater current capability.  But for
> streetcar lines, typically only the rails are used.  You have to remember
> there is a different history here.  When the streetcar lines were built,
> most streets were of dirt, and there were few houses.  Only the small
> central areas were developed.  The lines were built cheaply, and the impact
> of ground currents on pipes was not foreseen.  Remember, electric
> streetcars arrived on the streets  before electric lights and electricity
> in houses.  In many cases, the streetcar companies also became the electric
> power companies.  Eventually, the electric power business became the most
> important.  So, by the time the problem became recognized, the streetcar
> networks were mostly built, and the control of pipe damage became the
> problem of the towns.  In places like Cincinnati, the issue was not related
> to pipes, it was telephones.  In the beginning, the telephone circuits were
> one-wire, using earth for the return.  (cheapest way)  When the traction
> currents began flowing in the earth, the telephones became noisy.  In most
> cases, the arguments in the courts were won by the traction companies, for
> no one can claim he owns the earth.  But in Cincinnati, the traction
> company lost, and a second wire had to be installed.  I have not read the
> story in fine detail, so I cannot say just why that happened, but that is
> what I have learned so far.  Today, corrosion control is a serious
> business, and there are books on the subject, and expert consultants.  What
> surprises me is that in most cities there was not even a regulation
> requiring the traction companies to properly repair bad rail joints.  At
> least what I have seen indicates that to be the case.  I know that in
> Philadelphia, if there is any regulation, it is just ignored.  I remember a
> rail joint (a broken weld -there are hundreds on the system, all poorly
> repaired) on route 23 in downtown which was such a bad situation that after
> a PCC went by you could look down into the crack and see a blue glow from
> the electrical arc.
>
> Today, building new lines with paved track requires attention to the issue
> of  controlling ground currents.  Some have used rails which have
> insulating material poured around the rails (Portland) , some are placing
> rubber boots around the rails.  All of these help, but in the end it is not
> possible to provide complete insulation.  I don't know if anyone has also
> installed added cables to reduce voltage drops, and therefore, the earth
> currents, but it is possible.  I do not follow this subject closely, but I
> know there are technical papers about the subject, and I have some of
> them.  But I have not studied the subject recently.  Generally, in the
> past, the industry position was "our traction line was here first, if you
> want to put pipes in the earth,  it is your job to protect them".  But,
> since all the traction lines had disappeared, the new construction now has
> to observe that now it is no longer "first", and so it must do all that it
> can to prevent earth currents.  From an engineering standpoint, that is
> probably the correct way to do it.