We have been asked several questions about DCC bus wiring many times, so have produced this page which we hope will answer many questions that you may have about installing a basic DCC bus to your model railway layout. The information here was that gained when I started with a DCC layout. There was so much information available on the internet, that I got confused. There appeared to be no right or wrong way to wire a DCC layout, so I did what I thought was right and it worked. This page describes what I did, and the thoughts and reasoning behind it without going into too much depth. Regardless of what DCC system you use, you will be better off installing a proper DCC power bus.
All of our wires are of the highest quality and are all available in our DC and DCC Layout wire category. The wires are available in a wide range of single colours and in a range iof wire sizes. There is a help page on the specifications of the different wires available at the borttom of the page.
Please note that model railway electrics and electronics can be very dangerous. This website cannot be held responsible for injury or damage however caused by the use of any information on this website. If you are unsure about anything please ask a qualified electrician for help. Always fully read any instruction manuals supplied with any equipment and make sure you fully understand what you have read. Before using any electrical system you may have designed or made, please have it properly PAT tested to ensure that it is safe to use.
Model train locomotives need power to move, but how that power is delivered makes a big difference in how you can control them.
In DC systems, the power is supplied to the tracks in the form of a variable voltage, usually between 0-12V. Increasing the voltage to the tracks increases the speed that the Locomotive travels. By changing the polarity, the direction of the locomotive is reversed.
Generally, with DC, each locomotive requires its own controller and its own length of track which is isolated from ant others. Controlling multiple trains simultaneously on the same track can be challenging.
DCC systems use a half wave AC 16v voltage to power the tracks constantly that will make the locomotives move. A digital signal is used to control each train. Instead of changing the voltage and polarity to control speed and direction, DCC systems encode digital commands in a power signal. Each locomotive must be equipped with a digital decoder which will control the movement of the locomotive. Each locomotives decoder must be individually programmed which will allow for independent control of multiple trains on the same track simultaneously. DCC allows for more advanced features such as realistic acceleration and deceleration, sound effects, and lighting control. DCC systems typically require a command station, which generates the digital commands, and decoders installed in each locomotive to receive and interpret those commands.
When wiring up a typical layout you may need any of the following tools and
materials, regardless of scale and gauge of your layout.
Relying on joints in the track to transfer power could cause problems in the future which may include:
"What size wire should I use?" is the most frequently asked question from our customers
when it comes to first planning a DCC layout and its wiring. Given that most new DCC
systems have a power rating between 3 and 6 amps, selecting a suitable gauge of wire
for the power bus is very important to avoid voltage drop, and degradation of the digital
signal and to ensure the short circuit detection system will work at all times. A
small to medium sized layout with a power bus length of up to 30ft (10m) can be wired
with 24/0.2mm copper cable whilst anything larger than that should be wired with
32/0.2mm copper cable. It can be beneficial if you use a large wire on a small layout,
and it will allow you to have added capacity in case of future expansion or changes of
mind. Think about the future of your layout and if you are planning to add things
like sound and lights which you currently do not have, then build that into the layout
by using a larger wire.
All wire used should have an insulated cover. This is mainly for safety reasons. Some exhibition managers will not allow layouts that have been wired using un-insulated wires, regardless of the voltage and currents that they carry.
We also do not recommend the practice of using thin self adhesive copper tape as a bus wire. Whilst it does make soldering dropper wires easy as there is no wire stripping, we cannot find any maximum current rating on any of the copper tapes that we sell. Also although self adhesive, that fixing can fail, and often does, and there is no telling where it will fall and what it will come into contact with.
You also have to consider voltage drop. If your layout is large, you need a larger multi core cable to prevent this voltage drop. For example, a loco can draw 0.5A or more, lighting can be 50mA per carriage and the DCC bus can also power point motors, street lights, etc so a larger layout can draw several amps, with more than one loco running at a time. A typical 7/0.2 wire is limited to 1.4A but more significantly has a typical resistance of around 0.1 ohms per meter. Wiring a typical layout can use 10-15m of wire easily, so the wire would have a resistance of 1.5 ohms. At 1.4A this gives a voltage drop of 2.1V which could be enough to distort the signal to the point where a decoder struggles to interpret it. At higher currents, the loss will be greater still.
To maintain a high level of reliability where sound and lighting are
uninterrupted, it is good practice to connect every length of rail to the power
bus, and to isolate each length of rail from those next to it. Do not solely
rely on rail joiners to carry the digital signal and current no matter how good
the connection may seem. Rail joiners can work loose and could be a source of
"noise" in the digital signal. Now saying that there are layouts that work and
have droppers soldered to the rail joiners, so once again there is no right or
wrong way to do this.
Not all cable that supplies the track with power has to be of a large gauge. Whilst a minimum of 24/0.2 (4.5 amp) and 32/0.2 (6 amp) wires are good for the power bus, it is possible to use smaller wires for the dropper wires. Whilst single strand 1/0.6 (1.8 amp) or multi strand 7/0.2 (1.4 amp) can be used, we consider them to be too small, so recommend that 16/0.2 (3 amp) wires should be used to make the final link between the power bus and the running rails. This is the wire that we supply in all of our DCC starter wiring kits and on our pre-wired rail joiners. This works on the assumption that even a 3ft long piece of rail may have up to 2 locomotives working on it, and modern OO gauge locomotive motors are unlikely to draw more than 0.5 to 0.75 amps each under full load. All dropper wires should be kept as short as possible which will reduce any voltage drop and help keep things tidy under the baseboard. These figures may vary depending on things like whether the loco is fitted with lights and sound.
We sell a wide range of connectors to join the droppers to the bus, but you should really solder the connection, and then cover the joint with a heat shrink material or insulation tape. We sell scotchlok style insulation displacement connectors in two sizes. The red connectors are suitable for all of our wire sizes up to 32/0.2mm. The blue ones should be used for the 2.5mm tri-rated wires. These insulation displacement connectors make the job of wiring DCC bus systems easier, but should not be used with a solid core wire.
Easy one this. You can use any colour wire you want. Most people choose red and black, or blue and brown, but any colour combination can be used. Choosing two different colour wires for a power bus circuit makes things easier when it comes to joining the dropper wire to the bus wire as you can see what colour goes where. If you are adding more than one pair of bus wires choose a different set of colours. Two different coloured pairs of wires will help with fault finding. For individuals with color blindness or visual impairments, prioritize easily distinguishable colours. Consistency in colour selection is key, but feel free to choose colours that suit your preference.
If you read online about wiring a DCC bus, there appears to be no right and wrong way of doing it. Some use continuous runs of bus wires whilst others say not to do it and always have a break somewhere. I decided to build my power bus with a break, as that is what I thought was best at the time as there was no direct proof that one way was better than the other. If you could not leave a gap in the loop, you could not build end-to-end layouts. This is why we supply two termination filters in our kit, one for each end. Remember that the bus wiring not only supplies power to your locos it also carries the digital signal needed to operate the decoders inside the locos.
Adding a break or gap in your DCC bus wiring also means that you should also do the same in your track. What this means is that a continuous circle of track must have plastic or insulated joiners in both rails at some point in the circle to break the loop. We recommend that this is put in a similar place to the break in the bus wires, which should be equidistant to the controller feeds.
Now if you start to consider voltage drop in your wires, it is best to have the controller connection in the middle of this broken ring. I always suggest that people consider their power bus as a capital T or Y. The base of the letter is where the power inputs from the controller and is joined to the bus centrally to either end using the supplied large choc block connector in our termination filter kit. This will help with voltage drop as the length of any bus wire is about half the length of the track run.
If you are running two three or four main tracks, nothing is saying that you cannot run the same number of buses under the layout. This will enable you to keep the dropper wires as short as possible and will also permit the introduction of different power districts at a later date. They can for the time being all be wired into the larger choc block connector supplied in your kit. They can all use the same colour wire if you wish, but using different colours will aid any fault finding at a later date.
Now, after reading all that, if you want you can have a continuous circuit of wire. It is really up to you. It is also possible to feed your end to end layout from one end, rather than in the middle. Like I said at the beginning, everything seems to work.
Power districts allow you to have more control over the layout and the locomotives on it. It also helps to spread the power used across the whole layout and can be most useful on larger layouts by using more than separated one power bus. This does make the wiring a bit more complicated but can give better results.
A power district is a section of track that is powered separately from other sections of track on a model railway layout. Power districts also help with DCC power management. If you are planning to run lots of trains at the same time, you will need to make sure your DCC system can supply all your power needs efficiently and safely. Adding power districts to your layout can help with that. By dividing your layout into districts, you divide the total track power available into smaller more manageable pieces.
How many power districts you have usually depends on the size of your completed layout. Generally, you could split a layout up into up line, down line, and hidden sidings. That would give three power districts. You could also separate any large siding areas on the layout. For larger layouts, some power districts may have additional power boosters if they are a long way from the main power supply. Even on a small layout, though, you might want (or need) more than one power district. Separating a layout into power districts means that if one section becomes inoperable for some reason (like a short circuit, for instance) the rest of the layout can still be used whilst tracing the faults in the others. It is possible to have several power districts using only one power supply. Generally, every power district should have its own power booster and circuit protection.
When it comes to bus wires, one possible consideration is whether or not to twist them. Twisting the wires is believed to potentially minimize the interference caused by the inductive field between them. Extensive online research reveals a wide range of opinions from various "experts" on this matter. Some emphasize the utmost importance of twisting, while others dismiss it as a futile effort.
The basic principle behind twisting wires is to maintain their proximity, thus reducing the impact of the inductive field. Achieving the same outcome can also be accomplished by securely fastening the wires together using cable ties, or passing the wire through underboard cable securing clips. However, it is worth noting that twisting the wires remains a viable option and is unlikely to cause any damage.
Twisting your bus wires together is easy. Once twisted, however, it is harder to attach dropper wires. Worse, if your railway is already built, twisting your bus wires together is not an option. Therefore, it is recommended that you apply only about 4 twists per foot (or 12 twists per meter). If you twist all the wires before you attach the dropper wires, you may find it challenging to untwist the wire at the points you intend to attach the dropper wires. Try twisting the wire as you install the dropper wires. That is, twist the wire up to the point you intend to attach dropper wires. Then attach the dropper wires. Then continue twisting until you get to the next dropper wires.
Let us be practical about this. It is understood that when you run a track bus in the form of a twisted pair, you must untwist portions of the wire to permit one to make connections. Small or short untwisted sections will not ruin the overall benefit. The goal is to keep the far majority of the wire run twisted.
On long DCC bus runs, it could be worth adding a terminator filter kit to all open ends of your DCC wiring. The termination filter is a relatively simple cheap device that will filter out noise and voltage spikes created by the motors brushes, intermittent wheel to rail contact, and intermittent short circuits, and will improve the quality of the DCC waveform by minimizing reflections caused by the open end of the bus. Adding these low cost devices may extend the decoder life and will improve overall layout reliability.
The termination kits we sell, include two components, a resistor, and a capacitor. Neither of these items is polarity sensitive. A Capacitor across the two wires will cause a dead short to AC signals, such as the digital waveform used for DCC. The resistor is in the circuit to prevent it from being a dead short between the two bus lines.We also include two small 3 way choc block connectors which are fitted to the ends of the DCC bus wires and allow fitment of the termination filters and a larger chock block connector that allows you to join the power feed from the controller to the bus wires.
In an ideal world these snubber kits should be fitted onto every open end of your DCC bus wiring, but if you wire as a continuous loop of wire one can be fitted across the power bus wires at any convenient point.
Instructions on how to fit the termination kits that we supply and how to use the scotchlok style connectors can be found here.
Note: We have been made aware that certain individuals are experiencing conflicts and receiving false positives while using block/occupancy detection with termination filters connected to the power bus ends. In the case of employing block or occupancy detection technology and equipment, it is imperative to install the filter directly on the DCC bus wires end, rather than on a leg originating from the detector module. If you encounter such false positives, we recommend running the layout without the filters to determine the cause.
Many people just run the wires under the baseboard and then think that out of sight is out of mind. Over time your layout wiring can become quite extensive even on a small layout. When you start things may be small and simple, but over time when you add electric point motors, led lights for track detection, building lighting, electrically operated signals, and any other electrical accessory, it can become complicated and a tangled mess. Where possible come up with a colour coded wiring plan and keep to it. Try to keep your wiring neat and try to bundle wires that are going to the same areas together, using either plastic ties or clips. Secure the wiring to the underside of the layout to carry these wire bundles from one place to another. Label your wires so you know where they go or what they are for. Keep a written record of what you do to any wiring and why you added it. You will thank yourself many times over when you have an electrical fault in the future and all your wires are red.
It is all too easy to race along and wire the complete layout in one go. You should electrically test for continuity on each baseboard as you progress. Use a test meter to make sure you have good soldered joints to the track, and also good connections to the bus wires. Once you are happy, move on to the next section. It is also possible to connect up a controller to test that power can be applied, but do make sure everything is working fine before placing a loco on the rails. A short or bad connection will be easier to find now, rather than when the whole layout is wired.
The final test to be carried out before moving on is the coin test. This is where you place a coin across the live rails, creating a short, and see whether your command station shuts the power off. If it does it is all well and good. If it does not cut power you have to trace to find the reasons why. When carrying out this coin test make sure you have only the controller connected and no locos standing on any tracks as damage may be caused. DCC track signal is neither AC nor DC. DCC is digital data sent in the form of Pulse Width Modulation on the rails so only a purpose built DCC meter or an oscilloscope will give you an accurate reading. You can get an approximate voltage with a regular analogue or digital multimeter set to AC Volts.
You should first wire up the power bus in a simple way, to get the layout operational. If you wish to you can introduce further advanced wiring to assist with fault finding and power sub-division at a later date. This has the advantage of placing the layout into use much sooner and spreads the cost of ancillary power management equipment over a longer period.
This does mean that the layout can be run to test the track, layout, and operational capabilities, find faults, check turnouts and ensure turnouts are correctly wired for crossing polarity switching and many other things. Primarily, such testing will ensure that a good power supply is available with minimal voltage drop.
There are a lot of websites that say that 7/0.2 wire for the droppers and 16/0.2 electrical cable for the Power bus ring main should be fine for use as DCC bus wiring. I disagree. Saying that this setup would work for a small layout that would run only a few locomotives at the same time. We sell more 32/0.2 red and black wire for DCC bus cables with 16/0.2 wire being used for dropper cable than any other wire size. That in itself must say something.
Avoid using any non insulated materials under the baseboard, such as stripped electrical wire, copper tapes and uninsulated connections. They are generally just plain dangerous, and safety is important.
We offer a wide selection of DCC starter wiring kits for all sizes of layouts no matter what the scale. The components in the kits have been specifically selected, not only for their price, but for their quality. The kits include a high quality wire used for the power bus and a smaller wire for the dropper wires. Depending on the kit included are either insulation displacement type connectors or short pre cut lengths of heat shrink to allow the easy connection of the dropper wires to the power bus wires. There are small plastic P clips that are used to securely hold the wires to the underside of the baseboards.
Railwayscenics offer a wide selection of top quality DCC wiring starter kits designed to meet the needs of railway modellers. Our kits feature carefully selected components, ensuring both affordability and quality. Our kits include a high quality stranded flexible wire that will form the backbone of your DCC layout wiring. This wire ensures a consistent flow of power to all your tracks and minimizes any risk of voltage drop.
To effectively distribute power to your tracks, dropper wires are essential. These smaller wires connect the track sections to the power bus wire, ensuring that every part of your layout receives adequate power. Our starter kits come with dropper wires of suitable gauge, ensuring reliable connections and smooth operations.
Making connections between dropper wires and power bus wires can be a hassle, but not with Railwayscenics kits. Depending on the kit you choose, you will find either insulation displacement type connectors or short, pre-cut lengths of heat shrink. These options eliminate the need for complicated soldering and allow for quick and secure connections.
Keeping your wiring neat and organized is crucial for the overall aesthetic and functionality of your layout. That is why our kits include small plastic P clips to securely hold the wires to the underside of your baseboards, minimizing the risk of tangling or damage.
The final components included in the kits are Termination filters, or snubbers as they may be known, which fit to the open ends of the power bus wires. These small components are fitted across the wires and will reduce the risks of damage to the sensitive electronic components within modern DCC chips.
All our DCC products are listed in the electrical section under the DCC Wire Kits sub category.