Southern Digital

Layout Wiring

Layout wiring can be as simple or as complex as you need for it to be. Theoretically, all you need to do is connect two wires from the booster to the track, and, except for reverse sections, it will work. But we all know that most railroads need several sets of track feeders to operate smoothly throughout the entire track plan.

Nickel silver track is not a good conductor of electricity. Further, rail joiners can create a potential for interruption of power. So, you need to have track power feeders every six to ten feet. Even so, it’s still just two wires strung around the layout for feeders to be connected to the track in several places.

However, there are other things that can cause more complexity than this, such as reverse polarity sections, additional boosters to run more trains, additional boosters to isolate derailments from affecting other trains, and detection blocking for train position or signaling. But in all cases, it is always easier wiring DCC than it is for block control. The fact that you don’t have to wire all those toggle switches makes this self evident.

Even though the electrical polarity on the rail does not control the direction of the loco, you still have to contend with reverse sections. After all, if the track turns around back onto itself, the right rail will come in contact with the left rail. And that is a short circuit, the same as placing a metal object across the rails. Reverse sections are discussed at length in the section called Reverse Section Control.

Each booster has a certain amount of power that it is capable of providing. If you try to draw more than it is capable of, it will shut down. Usually before that, though, you will see a marked decrease in loco performance. For example, if getting close to the limit of a booster, you might see one train slow down slightly as another is starting up.

A typical Digitrax 4.5-amp booster is capable of powering about 10 HO scale locos – more if nothing but high quality locos are being run, less if all Athearn or higher drawing locos are being run.

One might think that the answer is to use a power booster that is capable of more power, or to parallel two or more together to place more power on the rails. However, placing more power on the rails can have the potential to melt things if a booster doesn’t shut the power off soon enough after a derailment. And, the more power there is on the rail, the faster the power must be shut off to avoid damage. So, for train control, the advantage is to have more smaller power boosters around the layout than to have fewer power boosters that will place more power on the rails. There is a side benefit of having more boosters as well, as later discussed.

To add more boosters, all you have to do is: divide your layout (trackage) into logical divisions of however many boosters you think you will need, cut the under-the-layout track bus at logical points to accommodate the trackage split, and connect one booster to each section. The boosters are connected together through network wiring so that all boosters are sending the exact same signals simultaneously. That way, when a loco crosses the track gaps that separate the power districts, the loco never misses a beat – without toggle switches, or anything else to think about.

When a derailment causes a short circuit, boosters are designed to shut the power down until the short circuit is relieved. The downside of this is that all other trains in the power district of that derailment will stop too. Many people opt to have a separate booster power the yards so that derailments in yards won’t stop the mainline. Some people go to the extent of breaking the mainline down into districts for the same purpose – even though they don’t really need more power.

If you’re planning to have train position indicators, or operational signaling, a certain amount of blocking needs to be done for train detection. Even so, it’s still easier than with block control. While it’s not realistic, we’ll say that the signal blocks in our example below are 12 feet long.

Select a rail to be the detected rail – the other one will be the common rail. If you’ve used two different colors of bus wires under the layout, simply select a color, and stick with it. That is, if you select white, for example, always connect the block detector to the white wire.

Cut the rail that is fed by the wire selected at each block isolation point. Connect the block detector to the track bus, and then run track feeders to that rail from the block detector, as shown below. The other rail will get it’s normal track feeders from the common rail bus wire.
(See Figure #1 Below)

That’s it. The rest of the wiring depends on what you’re going to do with that Detector’s – signaling, or control panel lighting.

Something to think about is that the under-the-layout track power bus needs to be large enough to carry all of the power needs. With cab control, the wires need only to be large enough to power one train. With DCC, the bus needs to be large enough to carry all the power the booster is capable of supplying – 4.5 amps, for example with a Digitrax DB210 booster.

Block Detection Figure 1
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