Here are a couple of hints to help
you figure out which portals are which, and how to wire them:
First, since the mainline itself doesn't
have a polarity problem, it's simply straight through with the same
polarity all the way, which means that all portals on that mainline
will be the same - in our illustration, both north portals.
Second, since the north portal on the
right can't be accessed by a train going from the south portal, don't
try to figure out which rail is 3 and 4 in the normal way. Treat the
north portal on the left and south portal as a simple two-portal reverse
section. Once you have those numbered, simply give the right north portal
the same numbering as the left north portal.
When trains use the north mainline
in the normal manner, in either direction, polarity does not reverse
(unless the last train went through from the north mainline to the south
mainline). It just stays set to the same polarity as the north mainline,
with both north portals having normal track power. Polarity will only
change when the crossover is used, and then be changed back, if necessary,
when the mainline is used again.
Note that the whole crossover isn't
used as part of the reverse section. By keeping the south portal close
to the north turnout, a train going from the south mainline to the north
can wait closer to the north mainline when it has to wait for a north
mainline train to pass. It's not that trains should be waiting closer,
but that this reduces the possibility that an errant engineer will enter
the south portal pre-maturely.
NOTE: When waiting for a train to pass,
the waiting train may not enter the portal until the engines of the
passing train have completely exited the reverse section.
If the south portal was placed as close
to the south mainline as possible, the train going to the north would
have to wait completely on the south mainline until the north mainline
train has passed. This would be OK, under normal conditions. But after
running with DCC for awhile, most people forget that there are still
foul lines that have to be accommodated. With the foul lines as close
to the real danger as possible, it's less likely that someone will foul
the line and cause a short circuit.
The same holds true for the north portal
to the right of the turnout. Keep it as close to the turnout as possible.
However, in doing so, you must insure that the points on that turnout
have good solid track power as previously discussed. |
