We have been asked several questions about DCC bus cable 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.
Please note that model railway electrics and electronics can be very dangerous.
This website cannot be held responsible for injury or damage how ever caused
from 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.
What is the difference between DC and DCC?
With a DC analogue system you only apply power to the tracks when you want a
locomotive to move.
With a DCC system all of the track is live all of the time,
so you can move more than one locomotive at a time on the same piece of track.
What materials and tools will I need to wire my layout?
When wiring up a typical layout you may need any of the following tools and materials,
regardless of scale and gauge of your layout.
- DCC power bus wire of 24/0.2 or 32/0.2 in black and red (or another colour
of your choice) depending on your layout size or scale chosen
- Dropper wire of 1/0.6 single strand or 16/0.2 stranded to match your
colour choice of bus wire.
- Suitcase style connectors to join stranded dropper wires to bus wires
- Wire strippers suitable for your choice of wire
- Soldering iron of your choice, but at least 25w power and preferable 40w
- Suitable flux
- Solder that is suitable for the materials used
- Small file or scratch brush to clean side or underside of track before
- Pair of pliers to close suitcase style connectors
- Insulation tape or heat shrink to insulate soldered joints
- Electrical test meter
- Drill and various sized drill bits to drill through baseboard materials.
Why do I need a power bus system under my layout?
Relying on joints in the track to transfer power can cause many problems
- Poor performance on longer layouts.
- Voltage drop leading to reduced loco performance.
- Distorted signals leading to loss of loco control.
- Limitation on the number of locos and accessories that can be powered.
- Short circuits can lead to loco or decoder damage as the control station cannot
detect these quickly and cut the power.
To ensure better running the costs involved in adding a DCC power bus is
small, compared to the cost of not having one.
How do I choose the correct size wire for my power bus?
Given that most new DCC systems have a power rating of 3 to 6 amps,
selecting a suitable gauge of wire for the power bus is very important to avoid
voltage drop, 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.
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
What is voltage drop, and should I be worried about it?
You also have to consider voltage drop. If your layout
is large, you need a larger multi core cable to prevent this drop in voltage.
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.
What size wire should I use for my dropper wires?
To maintain a high level of reliability where sound and lighting is
uninterrupted, it is good practice to connect every length of rail to the power
bus. 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 are
a source of "noise" in the digital signal.
Not all cable that supplies the track with power has to be of a large
gauge. Whilst a minimum of 24/0.2 for 4.5 Amp N and OO gauge layouts is considered
to be good practice, 32/0.2 for 6 Amps O gauge layouts, simple single strand
1/0.6 or multi strand 7/0.2 wire may be used to make the final link between the
power bus and the running rails. Our 16/0.2 wire has an outside measurement of
1.6mm and is also suitable. This is the wire that we supply in all of our DCC
starter wiring kits. This works on the assumption that even a 3ft long piece
of rail may only 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.
The above wire will carry up to 1.4 to 1.8 Amps easily. All dropper wires should be
kept as short as possible. These figures may vary depending on things like
whether the loco is fitted with lights and sound.
How do I connect dropper wires to the bus wires
We sell 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 connectors in two
sizes. The red connectors are suitable for all of our wire sizes. These
mechanical connectors make the job of wiring DCC bus systems easier, but should
not be used with a solid core wire.
Should a DCC bus be a continuous ring?
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. The general consensus is that a
DCC bus should not be a continuous circle, it should have a break in it. 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, its best to have the
controller connection in the middle on 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 of four main tracks, there is nothing 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.
What are power districts and do I need them?
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.
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 a number of power districts using only one power supply.
Generally every power district should have its own power booster and circuit
Should I twist the two bus wires together?
If you have long bus runs, you should really twist your bus wires. This will also
greatly reduce interference.
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 really an option. Therefore, it is recommended that
you apply only about 4 twist per foot (or 12 twists per meter). If you
twist all the wire 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 a dropper wires. Then attach the dropper wires. Then continue twisting until
you get to the next dropper wires.
Lets 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.
DCC bus termination/filter
On long DCC bus runs, it could be worth adding a terminator kit to all open ends
of your DCC wiring. The termination filter is a relatively simple device that
will filter out noise and voltage-spikes created by a 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 decoder life and
improve overall layout reliability. The termination kits we sell, include two
components, a resistor and a capacitor. Neither of these items are polarity
sensitive. We also include two small 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 allow you to join the power feed from the
controller to the bus wires.
Instructions on how to fit the termination kits that we supply and how to use the
scotchlok style connectors can be found here
Keep your wiring neat and organized
Many people just run the wires under the base board 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 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 the wiring and test using a loco. 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 and see whether your
command station shuts the power off. If it does its 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.
K.I.S.S. (Keep It Simple Stupid)
You should firstly 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 of time.
This does mean that the layout can be run to test the track, layout, 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 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 ring main should be fine for use
as DCC bus wiring. I personally disagree. Saying that, this
setup would work for a small layout which 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 it self must say something.
Avoid using any non insulated materials
under the baseboard, such as copper tapes, bare wires and un insulated
connections. They are generally just plain dangerous, and safety is important.
Please click on any of the images below to be taken to the products page to see full specification and components included.
|Micro DCC non solder
layout wiring starter kit
|Model Number: 218-009
||5m x Black 24./0.2
5m x Red 24/0.2
2m Black 16/0.2
2m x Red 16/0.2
10 x Scotchlok connectors
|Small DCC non solder
layout wiring starter kit
|Model Number: 218-008
||5m x Black 32./0.2
5m x Red 32/0.2
2m Black 16/0.2
2m x Red 16/0.2
16 x Scotchlok connectors
|Medium DCC non solder
layout wiring starter kit
|Model Number: 218-005
||10m x Black 24./0.2
10m x Red 24/0.2
5m Black 16/0.2
5m x Red 16/0.2
20 x Scotchlok connectors
|Large DCC non solder
layout wiring starter kit
|Model Number: 218-004
||10m x Black 32./0.2
10m x Red 32/0.2
5m Black 16/0.2
5m x Red 16/0.2
30 x Scotchlok connectors
|DCC Bus terminator
|Model Number: 218-006
||2 x 2.5w 150R resistor
2 x 100nF / 0.1uF capacitor
2 x Pairs choc block connectors
There is also a very good website by Mark Gurries with all sorts of DCC information which can be found here
personally find this page less confusing that the one by Brian Lambert.