Wiring a layout for DCC:

(Or, jumping in with both feet without looking)

by Ron Newby

Note: This article originally appeared in the October 2004 edition of “The Interchange” the newsletter of the Ottawa Valley Associated Railroaders and updated on November 16, 2010

(Disclaimer: This article is based on my own experiences and what has worked for me. This is by no means the only way of wiring a layout for DCC.)

In last month’s INTERCHANGE I explained how I chose my DCC system. This time around I’ll explain how I went about wiring my layout for DCC.

If you believe some experts out there, all you have to do is connect two wires from your command station to the rail and you’re good to go. While this is technically true, unless you only have a simple loop of minimum radius and nothing else that’s all you would need to do. But if this is all you’ve got, I don’t think a DCC system would be the way to go.

My first attempt to wire a layout for DCC was on a module I built that is incorporated into my layout. This module is a small industrial area with lots of switching. What better place to start. It is small (4′ x 1′) and I figured it could be wired in under an hour. So out came the trusty tools and time to get started before the mood left me. I started by installing two 12-gauge bus wires, one white and one black, from one end of the module to another. When I laid the track I didn’t install any gaps as gaps are not required with DCC (or so I thought), I then ran feeders from both rails at each section of track before and after turnouts. I even colour-coded the feeders, red for the north rail and black for the south rail. After all the feeders were installed I flipped the module on its side and wired all the red feeders to the white bus wire and all the black feeders to the black bus wire. An hour and half later it was time to flip the module right side up and connect the command station up.

After hooking up the command station to the modules and dreams of finally being able to run multiple engines without having to worry about throwing a gazillion toggle and rotary switches, I turned the power on. The command station did its thing and was ready to go. Put a locomotive on the track, select the locomotive’s address on the throttle and crank up the throttle. Nothing, the engine didn’t do a thing, maybe it’s time to refer to the manual (when all else fails, read the manual).

While reading through the getting started portion of the manual, I find out that one has to turn on the power to the track. OK not time to panic yet, follow the directions and voila, 4 beeps and the system shuts down. That’s not good, time to get the manual again and see what the beeps mean. OK I’ve got a short, no problem, maybe it’s the engine. Removed it from the track and tried again, same result, 4 beeps. OK maybe now is the time to start panicking. Time to flip the module back on its side and check out the wiring, maybe I had a moment of colour blindness and connected a wire to the wrong bus. The wiring under the module checked out, so I checked to make sure that I used the right coloured feeder to each rail, no problem there either. Discretion being the better part of valour, I decided to sleep on it and come back to it with a fresh state of mind later.

A couple of evenings later it was time to tackle the problem once more. First thing I did was gap the rails after the turnouts like you would a conventional DC system. Checked the bus wires with an ohm meter and still the short was there. Next I started cutting the feeder wires one by one till the short disappeared. Wouldn’t you know it; I had cut 80% of the feeder wires before I found the short. I knew I should have started at the other end. Further investigating and testing found out that a turnout, a brand new one right out of its package, was defective and was causing the short. After changing the turnout (after testing it first) and reconnecting the feeder wires it was time to try again. This time I was holding my breath and praying that it was going to work. Turned on the command station and let it do its thing, turned on the track power and no beeps. Now I was starting to get excited, put a locomotive on the track, select its address on the throttle and cranked up the throttle. The engine moved, success, ran that locomotive for the next half hour, grinning like a kid in a candy store the whole time.

I wish that the above was just a bad dream (or maybe a nightmare) but that was my actual first encounter with wiring my layout for DCC. So, what did I learn from all this? Wiring a layout for DCC is not as simple as I thought, but it isn’t all that hard either. Now that I have wired the rest of my layout (the part that is built at least) I use the following standards.

Use 12-gauge stranded wire for the bus wires. I used white for the north rail and black for the south rail (it’s what I had on hand). The reason for using stranded wire is twofold. It is easier to run than solid wire and it has less resistance. The heavier the wire the better, I would suggest that 14-gauge be the minimum bus size. As DCC uses a constant voltage the loss of resistance is its worst enemy.

Run 22-gauge solid feeder wires from both rails colour coded to simplify wiring. Again use red wire for the north rail and black wire for the south rail (solid wire is easier to solder to the rails). That way when you’re under the layout there is no confusion as to what wire is attached to which bus wire. Feeder wires should be a maximum of 12″ long. If longer feeders are needed, convert to 12-gauge wire. Run at least one set of feeder wires for every length of flextrack. Nickel silver track has even higher resistance than wire.

Gap both tracks, and block the layout like you would for a conventional DC layout. That way, if you plan to add signaling or track detection circuits at a later date, most of the work is already done. It also makes it easier to find shorts by dividing the layout into bite size pieces.

Gap the frogs of the turnouts. This is to prevent shorts from the wheels of the locomotives when they go through the frogs. Also test the turnout before you install it. This is easy to do before installation and is one of the hardest problems to detect if the turnout is faulty once installed.

I recommend that you build a simple tester that will instantly give you an audible alarm when a short is present. It’s cheap and effective, the only components required are Piezo buzzer, a 9-volt battery and a battery holder. I built mine from parts that I had on hand, but if you need to buy all the components, the cost is around $10. A note of caution, disconnect your DCC system from the bus wiring before connecting and using this tester.

Divide your layout into power blocks or sub-districts. This way if there is a short only the power block where the short occurs will be shut down instead of the whole layout.

  1. Be sure to locate all possible reversing sections whether they are reversing loops, wyes or turntables. Automatic reversers are required for these sections. These sections also need to be double gapped and isolated from the rest of the layout just like they need to be in a DC system.
  2. Mount all components in a centralized location. This will aid in trouble-shooting problems as you will not have to run around the layout checking out the different components. The only component I mount near where they are required are the automatic reversing units as they are fed by the track power and are not tied into the DCC system by any other means.
  3. If you use a block on your layout as the programming track (I use a separate track that is located at my workbench) install a DPDT switch so that that track can be used as part of the layout.

By using the above suggestions I have not had any further nightmares in wiring my layout for DCC and the one problem I did encounter (due to momentary colour blindness) was detected right away by the tester. Since I’ve been running my layout with DCC I’ve not had any major problems with the layout and the problems that have cropped up have been easily solved. Although some experts claim that wiring a DCC layout doesn’t require complex or miles of wiring,I have found that wiring your layout the same way you would a conventional DC layout with blocks will give you very reliable operation and detecting and eliminating shorts becomes a very simple task. The biggest difference in wiring a layout for DC or DCC is that for DCC, the blocks are wired to the main bus instead of toggle or rotary switches thus eliminating all the complex wiring.

If you would like to read more about this subject I would suggest the following books:

  • DIGITRAX’S BIG BOOK OF DCC by John Palmer. Although this book is based on Digitrax’s products a lot of the information in the book applies to any system.
  • DIGITAL COMMAND CONTROL: THE COMPREHENSIVE GUIDE TO DCC by Ames, Friberg and Loizeaux. This book covers most systems and has a few interesting projects in it.
  • DEMYSTIFYING COMMAND CONTROL by Don Fiehmann, RAILROAD MODEL CRAFTSMAN from Mar. 2001-Feb. 2003. This series of articles cover all aspects of DCC.
  • (Note: The above books were readibly available when this article was first written and they may be difficult to find today.)

    I would also recommend Allan Gartner’s website wiring for DCC at: http://www.wiringfordcc.com Allan’s site has a lot of good information on wiring your layout and switches as well as a forum for asking and answering questions on DCC.