In my September 2017 DCC Corner column I talked about using a common between boosters on Digitrax and NCE command stations and boosters. This is especially important when dealing with both centralized and decentralized booster installations. A centralized booster design is where all the boosters and command station are located together. A distributed design is just the opposite, with boosters located around the layout near the tracks they power.
I used to argue in favor of lining up the command station and all the boosters right next to one another, and in some cases I would still suggest doing it. If you have a layout where the command station and boosters can be placed in a central location and the power buses fan out from there to the tracks they serve, with minimal overlap, then that would be a good option. With all the components sitting next to one another it is easy to interconnect them, their wiring is kept short, plus it’s easy to trouble shoot when you can see any lights, and hear any warning and error sounds. The down side comes when you have to run parallel power buses next to one another to get from the central location out to all the track blocks on the layout. This results in overly long wire runs, increasing the chances of inductance related issues.
Now let’s look at the distributed arrangement. Many layouts have a pretty linear design with blocks located one after the other. If you run all your power buses out from a central point you’d have to run several of them alongside one another for at least part of the distance and that would be a waste of wire, and require some long runs. But what if you put a booster at the junction of two of those blocks? That way there would be no overlap and minimize power bus lengths. If you have two levels then you could run two power buses down to the lower lever and connect to two blocks there. Again, you’d have little overlap and shorter bus runs. You could locate your boosters at several points around the layout in this configuration and greatly reduce the lengths of all your runs. But how about interconnecting the command station and boosters?
When connecting boosters to a command station you have to have a cable, usually a flat telephone type cable, running between them. This cable sends out the basic low power DCC signal from the command station so the booster can boost it to final track power levels. Most manufacturers also suggest having a common wire running between them–this serves as a reference so that you don’t have problems crossing between power blocks, and autoreversing. So you would have to run a booster network around the layout but that’s a lot cheaper and easier than those longer power buses. And a single 14-12 ga wire can be used as the common wire. For optimal performance and to minimize electronic interference you would want to keep about 6″ between this network and any power bus running near it.
In the final analysis the important consideration in deciding which approach to use really comes down to picking the one that will give you the shortest power bus runs with as little overlap as possible.