"Sawney Beane" wrote in message
...
Bob Eager wrote:

On Sat, 17 Dec 2005 19:32:34 UTC, Sawney Beane
wrote:

When he asked if my tape was steel, I caught on. I had read
somewhere about the signal voltage in rails. That made it worse
because now I couldn't honestly claim ignorance. If anything could
have made the situation more embarrassing, it was to realize I had
started explaining about my invisible friends, Click and Clack, who
had told me to do it.

Do that round here and you'll get more than embarrassed - more like
several hundred volts!

I've read that even where rails carry traction voltage, they can
still carry signal voltage. It has something to do with impedance,
but I haven't read how it works.

Traction power is carried between the normal rails and a third rail. Never
done just using the two normal rails. So the normal rails only make up one
half of the power circuit. The crossing gate signal is between the rails.

Block signaling is done with an AC signal, transmitted down the rails to the
next signal station. If the next station doesn't receive it (because it's
shorted out by a piece of rolling stock), that signal changes to 'red'/stop
status and transmitts a different AC signal to the next block, which will
display 'yellow'/approach. That's an example mind you. There are about as
many different signaling conventions/circuits as there are railroads.

daestrom