Western Railroad Discussion > What does a railroad shunt do?

What's the purpose of the cylinders buried in the ballast that say "shunt" on them?

Also is there any lightning protection for the track circuits?

Thanks.

Chuck

A shunt is used to terminate certain types of AC-based "track circuits" (the simple explanation). There are lightning arresters in signal cases for various apparatus, including track circuits. Once used (fried), they have to be replaced.

Most shunts are related to Grade Crossing predictor circuits, they set the outer limits of detection for a particular grade crossing. All signals equipment is designed to resist lighting, but there is no such thing as full protection against a direct hit. Too much power.

Barry Draper

We have them marked for DTMF switches. You can't line the switch if you are inside the shunt limits for that switch (turnout).

barrydraper Wrote:
-------------------------------------------------------
> Most shunts are related to Grade Crossing
> predictor circuits, they set the outer limits of
> detection for a particular grade crossing. All
> signals equipment is designed to resist lighting,
> but there is no such thing as full protection
> against a direct hit. Too much power.
>
> Barry Draper

In my short tenure as an Electrical Gang helper for the NWP,
I used to work with the "GCP" circuits for the grade crossing sigs
around Petaluma, Santa Rosa and to the north of there. We had an
interesting piece of equipment called a shunt wire, that fitted
between the rails and had two screw clamps with pointed faces. When
these clamps were tightened to the rail enough to complete the circuit,
the result was ding-ding-ding and the gates came down. Cars
would stop, and motorists would curiously look for the oncoming "train."

But we were just testing the gates and making sure all the lights/bells were OK.
Maybe today there's a more modern way of doing it; but that was the way
it was done in the late 70s if you were on a signal gang. I also recall
checking the backup wet cell batteries in their ground boxes, on a quarterly
basis. Those were for activating the signals, in case of a general power
failure of the county utility. Edited to say: the NWP was mostly a "dark"
road where I was assigned; not sure what the procedure would have been for
a signalized traffic road; shunting the rails like that would make everything
go red, no? A gang would need Track and Time, etc? We just obeyed the Foreman;
he knew where the trains were.



Edited 1 time(s). Last edit at 08/27/2014 12:35PM by OldPorter.