[PRCo] Re: Ground currents

[Boris Cefer]

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.