DCC reverse loop wiring

Dave’s been in touch with a DCC reverse loop wiring problem.

As usual, there are lot of helpful comments at the bottom of the post already.


Here are 5 pics of the layout and a diagram.

Sorry for the mess but I’m trying to ballast the outside loop.

The problem is the reverse loops and how I should wire them.

I have NCE as my DCC control although I have it running on the outside loop via DC right now.

I understand I need to insulate blocks or districts, but do I continue to wire the track the same within the district ( Blue wire on the north rail, white wire on the south rail) and use a module for seamless transition? I do not want to use a DPDT switch if at all possible.

Thanks Al”

HO scale model railroad

DCC reverse loop wiring

DCC reverse loop wiring

DCC reverse loop wiring

DCC reverse loop wiring

Now on to Bob:

“Hi Al,

I’m in the process of building my dream model railroad similar to dangerous Dave’s.

The room is 20ft x 32ft feet with a triple track main.

Two of which run around twice and one that runs around once. All the rail is in and the wiring half done.

I have a long long way to go and other things keep getting in the way. But I will keep at it.

I will send a few pictures that I have under separate cover.

Best Regards


20x32ft train layout

20x32ft train layout

20x32ft train layout

20x32ft train layout

20x32ft train layout

20x32ft train layout

20x32ft train layout

A big thanks to Bob.

And who can help Dave with his DCC reverse loop wiring? Please leave a comment below if you can.

That’s all for today folks.

Please do keep ’em coming.

And if today is the day you get started on your layout, the Beginner’s Guide is here.



PS Latest ebay cheat sheet is here.

PPS More HO scale train layouts here if that’s your thing.

33 Responses to DCC reverse loop wiring



  2. Chris Sylvester says:

    Wow!!!! That’s a hell of a nice job on your layout gives me a lot of good ideas thank you for sharing the pics can’t what to see the end product !!!!! Chris

  3. Roland says:

    Regarding the reversing loop, there is an electronic module you can buy (from Digitrax, I believe) that controls the power to the loop. You insulate both ends of the loop, then power it from the module. It detects the momentary short as the loco passes over the insulating fish plates and switches the power, so that other than hearing a click from its relay you don’t notice anything. Much better than a DPDT switch!

  4. Dave Lockett says:


    Continue to wire the same way and use a module.

  5. keith mathews says:

    very nice let me know if I can help

  6. Jim Carr says:

    The Digtrak module works great but you must insure that your insulated reversing loop is long enough to take your longest train or you will have problems if your cars have metal wheels.

  7. wish i had the mony to doo one not to big but ithink befor i kik the bucket i might be able to built one smal one love you posts thank you

  8. ANDY SCHYHOL says:

    Fantastic, very inspirational. I can find the large space, but I would have to put all of my living room furniture in the garage.

  9. Dave – out of choice, I would use two different colour wires to feed the reversing loop section (as the polarity can be either way round). You should be able to wire it up via a reversing loop module.

  10. James Marek says:

    Gotta say I love the Heavy Duty Triple Track Truss Bridge. Going to be a real treat watching long freight and passenger trains snaking around your layout.

    Can you post your track plan?

  11. Al, In that all your posts are a learning experience for me, I am putting all of them
    in memory..My thought is that when I get a pile about two inches thick, I’ll put out
    a hard cover book ” The Train World According to Al ” I’m sure it will sell a million
    copies worldwide I can’t do any building now, my biggest layout was 15×20, HO
    DC…Double main with 36 inch curves. I built a power pack that would handle
    seven locos in consist although the rails got a little warm. I’m a retired loco
    electrician Federal Inspector for Conrail. My favorite is the GP 38-2. 8250 as I was assigned to it …..You will never know how much you are appreciated RJL
    when new.

  12. EsK says:

    Hey Dave, for the reverse loop: You can go DCC and use one of the many options available to make it an automated reverse loop.

    I just returned my Digitrax AR1’s and got DCC Specialties Quad Frog AR1 instead. That’s because the Digitrax AR1 is an older generation auto-reverser which uses relays and they are too slow for the newer solid state controllers.

    Digitrax AR1 is a good product but if you are buying a new reverser then it’s better to “future-proof” it. So you can go in for any solid state product (not based on relays).

    Please be mindful of the fact that with a reverse loop, your train will arrive back at the switch with the switch being thrown the “wrong” way to receive the train back. Since I use Digitrax DS64 for switching, I am going to install Digitrax BD4 block detector to automate the switching so that the switch gets thrown back to the right position when the train is approaching the switch on it’s return journey.

    Hope this helps.

  13. Mike candelori says:

    I love long straight aways. Coming along nicely thanks for sharing

  14. Good luck with the project Bob , you should be able to get a few ideas from some of my video’s …then there will be 2 Dangerous modellers ? LOL …Dangerous Dave

  15. Scott J says:

    I as well use NCE, and employ DCC Specialties solid state PSX circuit breakers for my power blocks, and PSX-AR auto reversing module for my layout’s reversing spur. As well, to get by the train length limitation for my reversing spur, I put a dab of clear nail polish in the gaps where the insulating joiners are installed at each end of the reversing spur. This way,, the reversing module senses the presence of the locomotive when it moves onto the rails of the spur and the metal wheels of the wagons/carriages are not able to bridge the gaps because of the insulating properties of the nail polish. Since I use just a dab of nail polish at each end-gap, by the time it dries it not only can’t be seen, it flattens out when the polish dries. If you go this route, you may have to adjust a timing CV for the breaker module adjacent to the PSX-AR to gain flawless operation.

  16. Graeme COLEMAN says:

    Dave, I use a Digitrax auto reverser, I chose the new solid state version as it is quicker to respond, [only by microseconds]. Bit being solid state should be more reliable over time. easy to set up. I did my wiring of the isolation block in a different colour pair as that polarity will change with each train entering. Make sure the isolation loop [block] is longer than your longest train to ensure there is no conflict between entering switching to one polarity and leaving switching to the other. I think other brands do similar products, but the Digitrax is great and easy.

  17. Don says:

    the bridges are really nice & the passenger train is as well, the whole layout is. good work, will look forward to seeing it finished.

  18. Rob McCrain says:

    Reversing Loops
    If the trains have any lighting or electrical pickups along them, the loop must be longer than the longest train you will run. The loop must be isolated at both ends. In other words, you should put isolation joiners/fishplates on yours as the loop leaves/enters the point/turnout on both ends. Use a solid-state automatic reversing loop controller. When I built a reversing loop on one of my n-scale layouts, my Z21 controller’s sensor and circuit breaker were too fast for any reversing loop modules I tried. I am sure there is a good, fast solid state reversing loop module out there by now. Try this, NCE AR10 Auto Reverser. It may work for you.

  19. Chuck Holsclaw says:

    I have 4 reversi g loops on my layout. 3 of them use Digitrax Ar1 auto reverser. There are easy to install. It has a potentiometer to set the trip current. Once installed and current set correctly, they work great. When my locos cross over the insulated gap, there is no delay at all. I have a solid state everser by Nce, the Ar-10. It works great as well. Again easy to install. Just make sure that your loop of track is isolated electrically on both ends or you will have a short

  20. robert dale tiemann says:

    a labor of love. its nice to see someone that is so into trains.

  21. Larry says:

    Thanks to all for the great answers to DCC reverse looping. Finally answers from people how have actually done it . Thanks again. And Al you are the Greatest for posting entries that solve problems.

  22. Duncan Macdonald says:

    our club is using PSXX AR for auto reversing. it seems to be the best on the market. it is also a circuit breaker. easy to adjust for current sensing train detection as well. if your loop is just a loop then any of the AR’s would work ok. if you have several areas involved in the loop like sidings then you may want to consider the PSXX AR.

  23. Norm Stafford says:

    All these nice tips on the “LOOP” I’m building a reversing “WYE” and need a little help on that if someone has set it up before.

  24. Gary M from Long Island says:

    Wow…… you guys have got some great train rooms……very jealous.

    Great info on the reverse loop. is this method only for DCC???

  25. Paul says:

    I’d recommend using a Digitrax AR-1 auto reverser for each reversing loop that you have. Just follow the instructions and you can’t go wrong. I have two on my layout that have worked flawlessly.

  26. Dave Harrington says:

    For Gary M on Long Island, I have an MRC Auto reverse loop module installed on both a loop and a Wye. Just isolate the 2 legs of the Wye from the main line.

  27. robert dale tiemann says:

    love it. really thought worthy design.

  28. Al Otis says:

    MRC also has a reverse loop module that I have been using for several years. Works seamlessly, very happy with it.

  29. Fred Gevalt says:

    Or….you can hold out (as I am) for “POB” (power on board) with a wireless R/C comtroller – no more dirty track and wheels to agonize over, and no problems with reverse polarity. In the meantime just work on your scenery, ‘cause the technology is coming.

  30. Paul R. V. Pawlowski says:

    Try a Tam Valley Depot DCC Dual Frog Juicer and Auto Reverser to solve your reversing concerns.

  31. Andrew Aves says:

    Gary M – Long Island
    I might be wrong but as far as I know these auto reversers only work on DCC. For DC one has to use a Double Pole Double Throw (DPDT) switch.
    The track in the loop must be isolated as described above and be longer than the length of the train.
    The train has to stop in the loop to allow the points/switches and the DPDT switch to be changed before the train can exit the loop.
    Andrew in Oz

  32. Red says:

    I’m jealous as I have the same Union Pacific train that I collected when I was 12-15 years old. My grandson has it now, but shows no interest so I am going to get it back when I have my layout finished.
    As Bob Hope would say, “thanks for the memories”!

  33. Red says:

    BTW, I am 73 years old now. So that was in 1962-1965 when I collected that trains set!

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