DCC Bus Question - Twisted?

Discussion in 'DCC & Electronics' started by kchronister, Jan 5, 2006.

  1. kchronister

    kchronister Member

    I know that it's sometimes recommended to run the DCC bus as a "twisted pair," the twisting supposedly reducing crosstalk potential.

    I'm wondering if anyone has thoughts/experience on that issue? I'll be running some fairly long buses, and would really like to use Nomex 12 gauge - having it all inside the outer sheath keeps things nice and neat (and I have a 250' coil of the stuff laying about).

    But that would not be "twisted"... ???

  2. kadidle

    kadidle Member

    Casey, I think running Romex might be a bad idea, you will get cross talk issues (the wiring will act like a big old antenna). I'm using heavy (12 gauge) speaker wire that is twisted. The price wasn't too bad, and it will more then handle the power requirements. How long is your longest run? A few feet would probably be ok, but more then that and you started picking up "noise" that could cause you more headaches then the "cheap" price of using romex...
  3. Gary Pfeil

    Gary Pfeil Active Member

    Disclaimer: Speaking only from my experience! I use 14 gauge wire, I have zero problems. None of it is twisted. Sometimes it is several inches apart, other times right next to each other. I believe the cross talk issue may only affect things when you start using detection systems that use resistance wheelsets. that is the part I'm not sure of.
  4. kchronister

    kchronister Member

    Gary - how long of a run do you have on that bus?
  5. rksstl

    rksstl Member

    Like Gary I use 14 ga wire seprated by about 3". I have about a 15' run with no problems at all.
  6. Gary Pfeil

    Gary Pfeil Active Member

    Well, lets see. I have the output of the booster run to a terminal strip and I have several bused attached there, routed to different parts of the layout. Eventually to be broken down further and breakers installed. For now, the longest bus is about 100' I did terminate the ends of each bus with a resistor and capacitor to make a snubber, based on something I read at the Digitrax Yahoo forum. I'm not sure its made a differance.
  7. railwaybob

    railwaybob Member

    With a run "that short", you shouldn't experience any problems. A larger problem would be how you connect your track feeds. Solder them.
  8. kadidle

    kadidle Member

    It also varies with the environment. I have a rather classified military installation (called a missile silo) nearly in my back yard, we get screwy hums and squeels in our phone lines, the only thing I can figure was the dropline was untwisted pair. We had the phone company put a buried line in, and when the installer came out, he put the twisted pair in, nice clean phone lines.

    RF can be funny, since you get harmonics and while something isn't on the devices frequency, the harmonics can be.

    If you can run straight without problems, then save the coin, if you get problems, twist them up. BTW, you can twist romex, however it's a pain and probably not worth the couple bucks for pre-twisted wires. 2-3 twists per inch are probably suffecient.
  9. caellis

    caellis Member

    I believe the 'cross talk' problem occurs when you run the cab control wires too close to the track power wires for distances of more than a couple inches. Signal coupling may then occur under these conditions.

    I don't think there is an merit in twisted wires for the track power in DCC.
  10. TazzyTazzy

    TazzyTazzy New Member

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