Laying Out Your Power Bus

I get all kinds of questions from folks about wiring issues and one common one is how main power buses should be laid out under a layout. Most layouts I’ve crawled under follow a pretty simple pattern with the bus running directly below the track and straight out from the booster, with feeders attached to the tracks directly overhead. I have seen a few with a branching pattern where sub-buses run out to feed a yard or short branch. Occasionally some folks get real fancy and install wiring that could be confused as a model of the human circulatory system. Another option is a star-shaped pattern where several main buses fan out from one central location. This is the pattern some manufacturers suggest. For an image of that one just hold out your hand and imagine your palm is the booster and each finger is a power bus, all radiating out from a central position.

The star design works well for a centralized power setup, with all the boosters in one location, but for large layouts a distributed design may be better. With this design the boosters and/or power managers are distributed around the layout near the tracks they power. This approach reduces the lengths of power bus runs and saves on the cost and trouble of installing a lot of extra wire. In addition it reduces your potential problems with inductance related issues such as voltage drops, loss of control, and decoder killer voltage spikes.

But, what about loops–modular clubs use them, and so do individuals. Many small layouts are nothing but loops–sometimes folded over or with branches in or off them. Actually wiring a loop is very easy, if you cut it in two. You can cut gaps in both rails making it in effect one long straight piece of track that just happens to have a big curve in it, with a long power bus feeding it. Or you can use multiple gaps and matching power buses. By cutting it up you are creating blocks that can be better managed with power managers like the PSX power saver series from DCC Specialties.

These configurations should all work and should not be prone to inductance related issues as long as you twist your bus wires, or keep total length under 30′ and amperage under 5 amps. Things start to get dicey when you’re using individual wires that are not twisted or zipped together. Using loose, individual lengths of wire is a great way to create inductance related problems. Why is this a concern? If the two wires are placed tightly alongside one another then the electromagnetic signal tends to cancel out inductance.

Another issue is electronic noise cancellation, both coming from the bus wires and from other electronic sources in the room. When the two bus wires are tightly twisted it will tend to reduce the effects of this noise. This electronic noise not only affects the DCC signal in the power bus, it also can impact on signals being carried in adjacent wires such as your throttle bus, and that is also a good reason for keeping about 6″ between them.

For my power bus wires I have been using a 100′ spool of 14 ga zip cord designed for use as speaker wire. Larry Meir, who designs all those neat devices like the RRAmpmeter and the PSX power managers, has told me that he measured the DCC signal on a 100′ length of zip cord speaker wire and saw no effects of inductance. Larry feels the close proximity of the two wires in the zip cord acted the same as if they were twisted pairs and inductance was eliminated.

So why would zip cord be a better choice than twisted pairs? Well, it saves all the work involved in getting those long sections of individual wires twisted properly. When twisting the wires you need to make sure that they actually are twisting evenly, instead of one wire merely wrapping around the other. The idea is to have equal lengths of wire in as close a proximity as possible, and twisting will do that, but so will zip cord. Zip cord also saves some money since a twisted pair of wires is about 1/3 shorter than the original untwisted pairs. Finally I figure that a lot of folks will be more likely to use zip cord than having to twist their own wires, and if they do that’s a good thing in my book.

15 comments

  • Here’s what I’m using for bus wiring, from Amazon.

    To get from the boosters to the distribution point in the center of my layout I’m using 12Ga red and black zip wire.

    For the distributed bus runs I’m using this:
    https://www.amazon.com/gp/product/B00J36SUWC/ref=oh_aui_detailpage_o06_s00?ie=UTF8&psc=1

    and for feeders (it’s red/black under the blue jacket:
    https://www.amazon.com/gp/product/B00M20G776/ref=oh_aui_detailpage_o07_s00?ie=UTF8&psc=1

    DanB

    • After reading the reviews on this stuff (14 ga.alum.) I would say you couldn’t run fast enough to catch me, and give me some or that wire.

  • Edward a atkinson

    Thanks for reply and yes, now I know what it is, it’s available in the UK. I don’t know if we have another name for it.
    Another example of two English-speaking countries separated by a common language!!! But I do love your ‘fall’ for autumn.

  • Larry, I know you have talked about the 30 ft. “rule” before. Actually, as you have said, you can have 60′ of buss, if you place a booster in the center of the 60′ spread. I’m thinking that if you have more than 60′ of buss, spread out from a booster, even with a booster in the center, you need more boosters!
    180′ of track with this arrangement would only need two more boosters, besides your original one.
    It should be noted that the total track footage can exceed the 30″ rule, if the trackage winds around and is not strait. It is the total wire length that counts, not the track length.
    Here’s a way to look at it. Draw an “S” on a piece of paper, then draw a vertical line down through the S. The line would represent the bus, which would be considerably shorter than the S (track).

    • Don–you said it in a nutshell–it’s the total length of wire not track. You can run a huge layout with a single booster if it is wired properly. The 30′ rule can also be ignored if you twist the wires or use zip cord since they eliminate the inductance issues. Of course plain old wire resistance becomes a problem with long runs of wire if it isn’t large enough in diameter to avoid voltage drops.

  • Where did this info come from? Now you tell us. I am already wired using separate lines.
    Will the stranded zip wire accept suitcase connectors okay? IE without cutting strands.?????

    • I’m using them as well and just plan to separate the two wires far enough to fit the connectors in.
      DanB

    • Max–my first post on this subject appeared here in March 2015, and there have been others since then, did you miss them? Do a search for zip cord and read what you missed.

      As for the suitcase connectors I use them on all my zip cord. I am sure they must cut into the individual strands but it is no different than using them with individual stranded wires. It does require slipping a knife blade between them and opening them far enough to get the suitcase connector in there but you’d have to do that with twisted pairs too. And as I have said before if your buses are shorter than 30′ and your boosters under 5 amps there is no concern.

  • I’m not clear on one thing Larry. Is the fact that in zipped wire, the two wires are held in close proximity to each other, the same as two unzipped wires that are twisted? Or, in simple terms, wires do not need to be twisted if they are held close together, as in zipped wires?

    • Don–it is the fact that the two wires are held in close proximity that counts. Zip cord obviously does that since they are molded together and twisting also brings individual wires close together.

  • Hi Larry, I meant to refer to the EB1. I’m not a fan of the light bulb solution
    DanB

  • Hi Larry,
    I purchased 14Ga. Automotive zip wire as it’s red and black for the main power bus. I also bought 22 Ga. solid wire that’s red and black fro feeders.

    My mainline is 145′ on both decks, but I can locate the booster(s) centrally so that I don’t go over 30′ on any one run. I’m going to use NCE DCC components, but have stopped short (no pun intended) of buying their circuit breakers, as I’m not sure if I should buy the more expensive DCC specialties PSX product. I plan to signal with LCC ( as soon as the products are cooked) and will pre-wire CAT5 throughout the layout. Will the NCE circuit breakers suffice in the scenario I’ve described?
    DanB

    • Dan–you didn’t say whether you meant the EB1 or CP6. The EB1 has adjustable trip currents and response times to deal with heavy current demands of sound decoders. The CP6 is your basic ballast lamp with 6 bulbs on a circuit board. It comes with 1 amp bulbs and you can buy 1.75 amp replacements. I have never been a fan of ballast lamps mainly because instead of killing current to a short they limit it to the operating amperage of the bulb. That said my friend installed over 30 bulbs on his huge layout and so far no problems and we often have 12-15 guys at an operating session. There is a good comparison of these two on the NCE Information Station webpage and I have written a couple posts here about ballast lamps with a link to another website that has a lot of info on them. Also my June 2017 DCC Corner column dealt with circuit breakers. It sounds as though you have done your homework and should have a trouble free setup.

  • Edward A Atkinson

    Apologies, but I’m a newbee and live in the UK. What’s Zip cord and would there be a UK equivalent I could buy over here?

    • Edward–here in the USA zip cord has traditionally been used on small appliances and table lamps. It is called zip cord because you can make a slit between the two wires and pull them apart like a zipper. It is sold here in small diameters up to about 18ga at hardware stores. The larger diameter stuff in the 14-12ga sizes can be ordered in rolls from companies who specialize in audio equipment as it is often used for installing audio speakers in homes and autos. Here is a link to such a website so you can get an idea of what I mean. The one issue is most zip cord comes with a clear Vinyl insulator but the moe expensive stuff has a red and black coat making it easy to tell the two conductors apart. However some comes with a copper wire and a silver (coated) wire so I have had no problems. Remember if you keep your bus under 30′ and use under 5 amps you need not worry about these issues.
      https://www.parts-express.com/cat/hi-fi-speaker-wire/1617