If you use a figure 8 design for a DC layout and follow the + and -. you will see that as the track curves to the left, the top rail (let's say +) will become the inside rail as the track curves back to the crossing piece, meaning that that track does not have to be insulated from the left track. The right track, however, as it crosses the top rail requires a small point of isolated material (usually plastic) to avoid a short. Contact is then resumed once the rail continues between the other track and can be non-insulated as it crosses the bottom rail and extends down and to the right to connect with the original track again. The other rail will require a similar isolated segment as it traverses the bottom rail to avoid shorts as described above. This short plastic rail segment is sufficient to avoid a short (having the wheel in contact with both + and - at the same time) and the locomotive still receives current from the other wheels which are not in contact with the isolated part.

Once the locomotive clears the crossing, it will continue normally. In a reverse loop, the locomotive is confronted by reversed polarity, as the top rail (+) merges into the bottom rail (-). This creates the situation, where, even if the switch track is isolated (to avoid a short when connecting the tracks), the locomotive will suddenly find the polarity reversed and will suddenly try to move in the opposite direction. This is where DCC comes in handy, as the locomotive will continue in the the direction of programmed travel, regardless of the polarity of the rails, as the decoder takes the voltage and directs the + and - current to the motor independent of rail polarity, solving this long standing issue.

My biggest 2 rail DC peeve was that when you inverted polarity, it would affect every locomotive on the rails. With Maerklin, you could reverse one lok while another was safely in a red signal (stop) zone and when the signal changed, it would continue to move in it's original direction, even though the other had changed.

Regards

Mike C

Most manufacturers provides crossing tracks that work without any problems. The PIKO K30 track piece is an example of this. All the frogs are plastic and it works fine. You as the user do not need to do anything special.

With regards to reversing loops. Automatic reversing loops are not possible with 2 rail DC. They are only possible in 2-rail digital operation (both Lenz (LK200) and Märklin (66846) provides auto return loop modules). The Märklin module has two options one is using short-detection, the other is using the built-in feedback sensor in the module. When using the feedback sensor you can also have the module automatically set the entry turnout to the opposite direction when the train is in the loop. The setup is dead easy and not a problem at all.

With 2 rail DC it is a messier job, you will need to wire up a contact of some sort and flip the contact manually when the train is in the loop.

There is no problem with crossing tracks and polarity in DC analogue. I have two on the layout and do not have any polarity wiring.

Once again, I am scratching my head.

What is the actual reality?

Is there a problem with using a crossing piece in analogue DC, such that it is like with Marklin, or not?

Please clarify.

Thank you.

Confused in Toronto (but not sleepless....)

Thank you, JCR, for clearing this point for me.

And thank you to Mike for the technical explanation as well.

Being lazy, I will find the right crossing so as to avoid the issue altogether.

My next question will be whether the K track is insulated so I can use the crossing for both systems.