Using DCC, does Polarity matter when hooking up a reverse loop as it does with block wiring?
It certainly does, unless you have an auto-reverse module such as a PSX-AR connected to the loop. With DCC, you're reversing the phase of the DCC command signal, not polarity; but having the phase wrong within the reverse loop can cause DCC equipped engines to stall when they cross the loop boundary at one end or the other.
If you're running only DCC, the PSX-AR eliminates the need for a toggle switch connected to the reverse loop, but if you will be running both DC and DCC, then the toggle switch will be necessary.
I isolated a section of track for in reverse loop and installed a Digitrax auto reverser (about $20) and off I went. It does make a little clicking noise but I have my hidden in a track side building and hardly notice it..
Model RR is Good Using DCC, does Polarity matter when hooking up a reverse loop as it does with block wiring?
You want to make sure the inside and outside track is consistent. It's not called polarity in DCC for argument sake it is. Just call it inside and outside and you'll keep it straight. with reverse loop you are of course changing that for the time the train in in the 2nd phase of the loop.
Springfield PA
A tried and true way to visually determine polarity is to draw a diagram of the reverse loop, using different colors, such as red and blue, for each rail. Reverse polarity will be obvious as the two different color rails meet, causing a short unless some measure is taken (e.g., auto-reverser unit) to prevent the short, as illustrated in the following diagram:
Alton Junction
By one of these and problem is solved. Cheap and works great. There are other options but why spend more for such a simple function. This unit works independently of the command station and can be used with any brand DCC system.
Added the url command.
http://www.modeltrainstuff.com/product_p/dig-ar1.htm
A nice thing about the AR-1 unit is it is adjustable so it has just the right sensitivity. Some other auto-reversers aren't, so if they don't work exactly right you're kinda out of luck.
Model RR is GoodUsing DCC, does Polarity matter when hooking up a reverse loop as it does with block wiring?
As the others have said, yes, the wires coming back on their partners, as the diagram above shows, still constitute a short. That is why you must gap the loop and also provide a way to reverse the polarity as the leading metal wheels move over the gap and complete the continuity path the electrons could not take due to the gap. They'll quickly resume moving over the metal tire of the first such wheels, and pfffzzzzt.....you have the short. Luckily, our DCC systems plan for such errors and the engineers designed in very quick and sensitive shorts detector circuits that will prevent your decoders from frying under the increased load.
I purchased one of the PSX-AR's and found it both easy to install and very effective. Very reliable. One of those things you quickly forget about because it is so effective.
-Crandell
BTW I believe AC and DC both have polarity, it just works a little differently. In AC one side is + and the other is -, and then they switch...then switch again, very very quickly. If you have the same rail trying to be + and - at the same instant, it causes a short.