2015-04.4: TMTV April 2015 Edition - Act IV

24 Apr 2015

Average: 4.7 (18 votes)
1:02:04 - April 2015 Act IV - Module wiring (2015)

Trevor's friend Chris Abbott returns to the studio workshop to help him wire his Freemo-style modules.  Chris presents multiple options for wire, connectors and tools, and helps Trevor pick the best ones to build rugged modules that are able to survive trips to model train shows.

Bonus: Review of Woodland Scenics' Just Plug LED lighting system ...

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This was a well laid out video making the wiring seem far less intimidating.  It introduced some very useful tools, had some great tips and addressed some of the areas that have raised concerns in the past such as the crossing of the power bus and command control wires.  Excellent value!

Congratulations this is an excellent tutorial on how to do high quality layout wiring. There were many instruction points that explained why to do a task not just how to do the task.  Although a long video it was very worthwhile. 

I am really happy to see a feature length clip in this series, well done on having presenters that are knowledgeable on the topic! I really enjoyed this edition

Hi Trevor and Chris

Good video thanks.I'm wondering why you didn't have a separate internal bus wire for the module, so if a module boards shorts then it can be disconnected which doesn't stop the rest of the layout from operating. Maybe you thought it wasn't required because there were no turnouts, or lots of trackwork. What situation if at all, would you run an internal bus wire per module. If you did have a separate wire for the board would you use the same 12 gauge landscape wire for internal board bus. Interested in your thoughts. Regards Damo

tpmarshall's picture

Hi Damo:

Thanks for getting in touch, and it's a very good question. I'm not sure when we'd use an internal bus - in part, because the S Scale Workshop has no large, complex modules and partly becuase if we have a short we would not be able to run trains across the length of the layout anyway. I suppose we would quickly identify the short, fix it, and get rolling again.

As you note, the two modules I built have no turnouts. That means it's highly unlikely that a short would be introduced, since shorts on modular layouts typically (not always, but typically) occur at complex trackwork (for instance, because a rail has shifted in a turnout.)

Regardless, of the wiring scheme, the size of the wiring would remain the same - 12 gauge landscape. Wiring is only as good as the weakest link and there's something to be said for being consistent in one's wire choices. While the 12 gauge landscape wire might seem pricy, it's a bargain compared to the overall cost of building modules, transporting them to shows, and staying in a hotel. It's also a bargain to not embarrass oneself in front of fellow modelers or let down one's collagues in the club who have made an effort to bring their best to the show.


- Trevor

I'm curious that you did not twist the track bus. Also, with a long bus with such lash ups of lots of modules as shown at the train show, I would have expected some provision for snubbers even if it was just one in your spares kit attached to Anderson connectors. I had not seen Anderson connectors before but that was of great value to me.

I really like the buzzer approach and the good attention to the joints as well as the warnings on suitcase connectors. Thanks for the crysttal clear coverage of issues and practice.




Hello Greg,

There are many more topics which can be covered on the subject of DCC. This video (despite its length) wasn't able to cover them all.

Twisting the track bus wiring and adding bus termination are both good ideas. In the case of a home layout where the track wiring is a fixed configuration, and the signal distortion can be accurately measured, I would adopt both of these methods.

Getting a group of widely separated people to consistently execute a more complex way to wire their modules is difficult and error prone. Risks must be assessed and compromises made in order to obtain consensus and increase the groups’ chances of success.

One accepted practise to reduce interference without twisting the wires is to keep track bus length to 60' (or less) per booster section. Each booster would be located at the midpoint of its run and connected to the track bus with a ~5' tee cable. Keeping the run lengths this short will reduce noise that the cable picks up and imparts on the DCC signal. Where the track bus ends at the interface of the last module in line, insulated rail joiners isolate the next module group and their booster from the previous group.

I am leery of adding bus termination without being able to observe the effect on the waveform. I was able to clean up the signal on an On3 (NCE DCC equipped) layout to remove overshoot & ringing by monitoring the waveform with an ancient analogue oscilloscope. The default RC values offered by websites such as WiringForDCC are good starting points, but were too much for that situation (really rounded off the crests). I tested 3 or 4 combinations before I was satisfied with the shape of the signal. Performing this same task on a modular layout of variable shape and length is more than most groups would undertake. Again, keeping the track bus run lengths from each booster short (as above) will reduce the capactitive load that the cable imparts on the signal.


Chris Abbott

tpmarshall's picture

/\ This is why I asked Chris to come on the show and help out with the wiring for The Roadshow project modules. /\

My approach to wiring has always been, "If something doesn't work, don't do it again - and if something does work, do." Chris actually starts from a position of knowledge. I'm glad I have him to answer questions like this. Thanks Chris!

- Trevor

Thanks Chris and Trevor,

I have always been curious about twisted power bus cables. I would expect that the parallel spaced wiring you showed would yield higher RF but less waveform distortion due to reduced capacitance compared to just twisted figure 8 or just individual wires as a twisted pair.

You guys were using digitrax and that has the DCC waveform present on the loconet from memory so my expectation is that is where booster input signal is coming from. Had the system chosen been nice say, would it be better to run a pair around the modules to carry booster signal or just use the track bus from one module as input to a booster in an adjacent module?




Hi Greg,

A tradeoff for improved waveform using twisted bus wiring would have been marginally increased difficulty in ensuring correct bus-wire-to-rail connectivity. We use end-for-end swappable modules with genderless interface plugs (and are now employing local track bus circuit breakers) which must all maintain proper signal phase relationship regardless of orientation. This is not too difficult on a lone 4-foot module, but we have a few multi-section, multi-track module sets to contend with as well. A compromise between initial build complexity, future troubleshooting ease, waveform shape, and system reliability had to be struck.

Yes, the group's modules are intended to operate using Digitrax. There are ways to make a throttle bus somewhat system-independant (i.e. allow use of either Digitrax, NCE or Lenz system without having to change throttle panels) however, at the outset, most of us already had Digitrax equipment to be used as primary power, expansion, or spares as the need arose.

Loconet provides the basic (unboosted) DCC signal  as well as managing throttle messaging and control/detection accessory data traffic. Other systems have separate throttle and booster circuits. Either way, booster traffic should be as isolated as possbile from throttle traffic. I would never use the output of any track bus to feed a booster signal input; these connections are not designed to handle high amperage feeds or deal with track short conditions.

In our typical setup, all boosters and the command station are daisy-chained with a 6P4C data cable to one of the command station's RJ jacks. The other RJ jack connects to the end of the daisy-chain of throttle panels that serially link all modules in the layout. A separate, 14AWG ground wire is connected between the boosters and command station. On the Loconet chain, we also include either simplex or duplex radio transceivers for wireless throttle support. We could eliminate the wired throttle bus entirely, but that would prevent use of comparatively inexpensive wired throttles (including the excellent "FRED" from Europe) and elimiate the option of "plug-in-to-recover-runaways" that inevitably happen at shows. 

DCC is a deep subject; we're barely scratching the surface in our exchange here. More details can be found at the WiringForDCC and Digitrax FAQ sites,

best regards


Good show. Chris reminds me of a writer named Kevin Cameron, who is a regular contributor to a motorcycle magazine I read. He has a deep well of engine and chassis knowledge and has theoretical, academic and practical application experience.  His gift is the ability to distill complex ideas into words that I can understand. Chris has this same gift, and so was the perfect person to have on this segment.  Even more expansive explanations would have been welcome. 

On the down / up side, I have various new tools in the post to my house, and am exploring whether the Cooper products plugs can be applied to a static layout (to allow tool-less isolation of a various sections).