A 90-inch water main runs parallel and is in close proximity to a Chicago Transit Authority (CTA) DC
electric railroad. Prior testing indicated the presence of DC stray current interference on the 90 inch
pipeline due to the effects emanating from the DC electric railroad. This ultimately led to more
advanced testing and design of a bond using a reverse current drainage switch (RCDS) to mitigate the
interference caused by the DC electric railroad.
A reverse current drainage switch is a device that allows current to flow through a bond when the
potential of the pipeline is more positive than the potential on the railroad. By utilizing this type of
switch, the pipeline does not become more anodic as would be the case when DC stray current
interference is present. Once the potential of the pipeline becomes more negative than the potential of
the railroad the reverse current drainage switch opens to hinder the current flow in the bond.
This paper discusses the final commissioning and testing performed on the reverse current drainage
switch installed between the pipeline and the DC electric railroad.
Key words: Dynamic DC current interference, cathodic protection, reverse current drainage switch
(RCDS), pre-stressed concrete cylinder pipe (PCCP)