Wiring DCC

[Anonymous]

I model N scale and hope to move to DCC control soon. I'm still in the early stage of my layout; I was hoping someone might be able to tell me how simple or complex the wiring will be for this system. Do I need specific connections in particular places or is a direct power supply all that is needed?

[Anonymous]

Hello René,

Wiring for DCC is simple compared to wiring for DC cab control, especially cab control systems with more than two throttles.

You'll want to install a bus wire (I use 14-gauge solid strand, with red for the positive and black for negative) under the layout generally tracing the route of the main track (main line or branch line). I'll touch on why a bus is needed for trains in a moment.

Every six feet or so you'll want to drop a set of feeders from the rail to the bus line. Despite early claims for DCC, one set of feeders is not enough, not even on a small layout. Use barrier/terminal strips between the feeder wires and the bus wire to make troubleshooting easier and wiring neater.

A bus wire and multiple feeders solve two problems simultaneously. First, there's the issue of voltage drop through the rails. The further from the point of contact where electricity is fed in to the rail, the lower the voltage. That's because rail, like wire, has a resistance value. The resistance value is typically higher with rail because it's smaller and made of an nickel-bearing alloy, not copper.

Second, and very important for DCC, is that the command station and locomotives must receive a clear digital signal. Otherwise decoders won't function and the system won't detect a short circuit. Should a locomotive create a short circuit and the system not be able to detect it, the decoder can be damaged or destroyed.

Some manufacturers mention the "quarter trick," laying a quarter or other conductive item across the rails to short out the command station. This doesn't harm the command station because it's equipped with a fast-trip breaker circuit. But if you place a quarter across the rails and the command station doesn't trip out, it means the digital signal isn't sufficient at that point. A set of feeders is needed, and they should be connected to a bus wire.

The heavier bus wire has much less impedance per foot than rail, which is why is we rely on it to shoulder the voltage load rather than running feeders back to a common point. Plus it makes for a neater wiring job, and when wiring the neater the better.

Hope this helps,

Paul Schmidt
Contributing Editor
Trains.com