Bob Jacobsen in his
response and recommendation is exactly correct. I am certain that the problem
you are experiencing is a result of incorrect block wiring and/or
incorrect rail gap placement creating what I refer to as "sneak
circuits". That is, there are multiple paths, connected through
multiple detectors, for the current flowing to detected track sections.
All it takes is one
feeder drop from the detected rail of a given track section(say detected
section A) to be connected to a wrong detector (say detector B) while
all the other drops are connected to the correct detector (say detector
A) . With this you have a low resistance path from detected section A
to the correct detector A and you have a slightly higher resistance from
detected section A to detector B.
Place your hand across
the track at Section A and only the correct Detector A shows detection as
it should. This is because the great majority of the feeble current generated
through your hand into track section A goes through the lowest resistance
path and not enough of the current goes through the slightly higher resistance
path through Detector B for detector B to show occupied. Thus placing your hand
across blocks all seems to be working fine.
Now, place a locomotive
in Section A. Being a much lower resistance, a much heavier current flows in
Section A. It divides, just like in the previous case, but now the portion
flowing through Detector B is sufficient so that Detector B as well as
Detector A show occupied and the problem is exposed.
One of the ways to
determine where "sneak circuits" exist, is to unplug all the
detectors. Then plug is one detector at a time leaving all other detectors
unplugged.
Then with DCC power
turned on, set your Volt-Ohm Meter(VOM) to measure AC volts and connect the
red lead to the common "S" rail and use the black lead to check every
N-rail location of your entire railroad to see where you have track power. The
only location where you should read track voltage (12 to 14 volts AC for most
meters), is in the track section corresponding the detector that is plugged in.
I the above test
determines that you have voltage outside of the detected section, then you have
a sneak circuit that must be located and removed.
Repeat this procedure
for each detector on your layout.
Once every detected
section correctly powers only that section and no other section, then you
should be home free.
Bruce Chubb
