Talk: No Common Rail Wiring
This page seems to imply that DCC layouts cannot be wired with common rail wiring under any circumstances. But nowhere does it give a reason for that.
What this page should really be saying is that large layouts should be divided into booster districts, and when that is a requirement, common rail wiring cannot be used.
Smaller DCC layouts with only one booster will work perfectly well with common rail wiring
Common rail can be used, BUT:
If there is more than one booster or an autoreverser involved, if the polarity becomes mismatched the track voltage will be doubled, resulting in blown decoders.
Therefore it is easier to say do not do that, double gap the rails so any future changes will not result in disaster. The only real reason is stated is cost, but that isn't correct as you should feed both rails, not just one at regular intervals. With double gaps and proper wiring, all boosters and autoreversers will be tied together on a "common rail" between their "ground" connections, which prevents other problems and allows current to safely flow between boosters, not between the rails and fry the decoder.
Terminator (Admin) 19:32, 11 April 2013 (EDT)
I agree with what your saying, it's just that I think the article needs to have a more neutral tone. As it stands, it perpetuates the myth that layouts have to be "wired for DCC" or when converting an existing layout from analog to DCC it has to be "rewired for DCC". Now this may be true for large layouts with multiple boosters and/or reversing loops, but for the majority of modest layouts (as are more common outside North America) it is trivial to convert to DCC even if common rail wiring was used. You simply swap out the analog controller for a DCC controller. If multiple controllers were used with common rail wiring then you simply short the other rail feeds together and wire up a single DCC controller.
All that really needs to change in the article is that it needs to be explicit that what it is recommending applies to larger layouts with multiple boosters or that might have multiple boosters in the future.
As an aside, I don't see how common rail wiring with multiple boosters could blow a decoder (ignoring reversing loops for a second). In fact quite the opposite, a single gapped rail would guarantee that one rail is always "ground" and the other is either +16v ot -16v. So the rail to rail voltage is never more than 16v. Now I can see that the voltage across the rail gap could be doubled if the polarity of one booster was wired wrong, that would be 32V, but that still wouldn't blow the decoder since that 32V would not be across the decoder. I can see how it might overload the locomotive pickups though, with the full power of the short between the boosters flowing up one locomotive pickup at the front and down another locomotive pickup on the same side at the back. I agree that would be very bad and a very strong case for not using common rail wiring on a layout with multiple boosters.