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Wiring for DCC in general.

[edit] Wiring Complexity

Wiring for your layout can be as simple or as complex as you need. Potentionally, all that needs to be connected to your track is two wires from the booster; not accounting for reverse sections. However, as we will learn from this page, we need several track feeders in order for the trains to operate smoothly around the entire layout. The feeders typically connect to bus wires. As you can tell, the complexity of your layout determines the complexity wiring required.

As you read this article, and other DCC wiring articles, you will find that wiring for DCC is always easier than for analog cab control.

Additional wiring complexities:

• Larger layouts will need additional booster(s) to power more trains.
• Detection blocks to determine where trains are.
• Transponding for advanced computer train control.
• Reverse sections for reverse loops.
• Signaling for realistic operations
• Computer assisted or complete computer control of your layout.

[edit] Tools

First things first. You'll need some basic tools.......

• Short circuit detector (build home made one for a few dollars using radio shack parts - see below)
• Wire strippers
• Electrical Tape
• Diagonals
• Linesman's Pliers
• Pliers
• Screwdrivers

[edit] General Tips

[edit] Use a short circuit detector

IMPORTANT - Build a Short Detecting Beeper BEFORE You Start ANY DCC Track Wiring!

When doing any wiring on a track segment, you should connect a buzzing short circuit detector to the track block you're working on. This will help you detect shorts before soldering a connection, unless you really like having to cut newly connected wires until the short is found! You can build one of these using some cheap Radio Shack parts.

How to wire the short circuit detector.

Items needed:

• 18-22 gauge wire (just a few feet)
• 2 Alligator Clips ~ $3 each
• Radio Shack 273-059 buzzer ~ $3.50
• Radio Shack 270-325 9V battery clip ~$2.00
• 9 volt battery

To use, you simply attach an allligator clip to each rail you are wiring. Make sure you disconnect your booster - it may show up as a short and/or fry the buzzer. If there is a short between the rails, the buzzer will go off so you'll quickly know there is a problem.

If you have several boosters (or power districts), you will need to move the beeper to each district as you wire. If there are several teams wiring different districts at once, just make them each a buzzer - they're cheap insurance!

[edit] Develop A Color Code...

...And Stick To It!

It's best to develop a color code when you're just getting started. Whatever the code is, stick to it! It may help to buy your wiring locally, so that if you run out, you can call at the store and buy more. This will help you keep to your color code.

Need suggestions (or example) on color codes? Based on the fact that many modellers want to use regular house wiring, so lets start there. Use white and black from your booster out to the tracks (note: this is not the wire you use to connect directly to the track, this is the main bus wire), remembering that feeds between booster districts are NOT to be connected together! Red and yellow for reverse buses. All that is left is to pick two more colors for bus feeders (sub buses), such as blue and orange.

If you use the bare copper wire as part of your feeder system, be very careful it doesn't contact anything that is grounded to your home wiring.

Digitrax suggest a wiring color code: use this or use your own - it's your choice.

[edit] Get wire from a favorite home improvement outlet

The advantages are numerous. The most important one is that if you run out of wire, you can easily get more, which helps you stick to your color codes. As a benefit, you may get a better price than an electronics supply store.

Heavy stranded wire. At Home Depot, they stock:

• 14 AWG: Black Beige Red Blue Green White
• 12 AWG: Black Red(Rose) White Blue Orange Yellow Brown Green
• 10 AWG: Brown Orange Yellow Black Red Blue White

Similar stock is carried at Lowe's and other big box home improvement stores. Check your local options!

Heavy solid wire for wiring homes. This stuff is cheap, so you may want to base your power distribution buses on this. It is stiffer and more difficult to work with than stranded wire, so try it out before committing yourself.

[edit] Aluminum Wire

If some kind soul offers you aluminum wire, graciously accept it.

Then take it to a recycler, and use the money he gave you to buy copper.

Aluminum wire isn't readily available anymore, because of various issues surrounding it's usage. Aluminum requires special techniques, materials and devices to use it, and for the average person, this will be nothing but problematic. Therefore, for ease of installation and long term reliablity, don't bother with aluminum. Stick with copper, as it is easy to work with, and reliable.

The only advantage aluminum has ever had over copper is that the equivalent conductor is lighter and cheaper. Copper's advantages more than outweigh the cost difference between the two.

[edit] Don't use common rail wiring!

In wiring for DC, modelers usually had a wire that was common to all blocks, in other words the rail it connected to was ungapped over the whole layout. Even though this worked for analog control, do not be tempted to use the same method for DCC wiring. Do not use common rail wiring. (see also the article on Wiring) Do not connect any of your booster outputs together. This can cause shorts to occur, or boosters fighting one another.

Most manufacturers tell you not to have a common rail or a common wire between booster districts. This is just here to help them make the point clear. Gap both rails whenever you make a gap. Do not run any power or programming wires from one booster to another.

If you have an existing layout, you will need to gap your track and cut the common wire. Make sure you don't forget to cut the track when you cut the common wire.

In the booster network wiring section, you will read that you should connect the grounds of your boosters together. This is different than connecting your booster outputs together. The grounds of your boosters should be connected together.

[edit] Wire size

(I'm just putting this layout here, someone else will need to fill in the details.. TazzyTazzy 16:03, 14 December 2005 (EST)

I've added the N scale info and the intro - has any group done any studies for other scales? Joe Ellis 01:18, 15 January 2006 (EST)

Are these wire sizes overkill? It might appear to be so, but experience has shown that because you can run more trains with more locomotives on DCC, you usually will. This means your electrical loads will be higher for a given layout. In addition, a voltage drop of just 2 volts is a problem with DCC, and you can't compensate just by cranking the throttle up. Keeping these factors in mind, it's clear you need heavier wire. A small table top layout can reduce these sizes a little bit without problems, but larger home or club layouts should adhere to these suggestions - you'll appreciate it in the long run. It's cheaper to do it right the first time than it is to tear it out and do it over!

The important issue with wire gauge is resistance. Heavier wire (a smaller gauge number) has less resistance than light gauge wire (with a larger gauge number.)

The resistance causes energy loss when current flows through the wire. This is lost through heat. The result is a drop in voltage. This is expressed as I^2R loss (I Squared R). When current flows through a resistor, a voltage drop is created, equal to the current multiplied by the resistance. The energy loss equals the current squared, times the resistance.

Basically, if a loop of wire has one ohm of resistance, and you pass 1 amp through it, you will see a loss of one volt. If you pass 5 amps, your loss is 5 volts. If the resistance is doubled, that loss increases to 10 volts.

For the most part, the resistance of copper wire is so small that it is usually expressed as ohms per 100, or 1000 feet. For a short run of a few feet, the resistance is negligible. But it becomes an issue for a long run of wire. Remember, an equal length of wire is needed to complete the circuit, doubling the resistance of the circuit.

An important concept that is often ignored is the way the circuit protectors work. They are not sensitive to the amount of current. They react to the rate of change in current. A sudden spike will trigger them.

Poor wiring will interfere with their operation. Which could result in damage to your locomotive, or it's decoder, because too much current was flowing, resulting in excessive heat. Or a short occurs, and something melts because the power was not interrupted. This happens because the wiring isn't heavy enough, interfering with the rate of change the booster sees. Or the voltage drop demands more current to maintain the same amount of power. A change from 1A to 1.5A in draw will also increase the power dissipation by more than twice.

Good heavy wiring goes a long way to preventing problems like that. Using AWG 14 or heavier is not overkill for a bus, and track feeders of AWG 18 are not that heavy. Choosing wire because it is cheaper or easier to hide is just asking for problems.

[edit] Wiring

[edit] Bus Wires

Bus wires carry the power from the booster to the track, but don't directly connect to the track. Feeder wires handle that task.

Below is some information to get the most of your system but using the correct wire types, gauge, and installation methods.

You can use either solid or stranded wire. Stranded wire is more flexible and will better handle repeated bending.

[edit] To twist or not to twist

There is a large debate on wire twisting of track bus wires. Compared to two parallel wires spaced closely together (1mm), the reason for twisting the same sets of wire is to help cancel any radio interference. A twisted (balanced) set of wires helps prevent radio waves from interfering with the DCC signals. These interferences could be interpreted by loco decoders and could cause havoc on the system.

The negative side of the coin is that attaching feeder wires to the bus wire could get complicated if you are not consistent with your color coding, however, the wires are not twisted a great deal so it shouldn't be too difficult.

Generally, you twist the wires around each other about two or three twists per foot.

You should consider twisting your bus wires if they are going to be 30 feet or more. Twisting is more important on outdoor tracks where bus runs can sometimes run a 100 feet or more. If you compare two long and widely spaced wires (inches apart) with two long but closely spaced wires (1mm apart), the latter have a lot less inductance which is better. The amount of inductance you have in your wire directly relates to the degree of DCC waveform distortion and other problems such as large voltage spikes. Large voltage spikes are created during intermittent short circuits caused by derailments or other electrical track issues. Waveform distortion can cause havoc on a system while large voltage spikes can be harmful to decoders. If you twist two lose and widely space wires together, you will achieve a neat and consistently closely spaced set of wires giving you both lower inductance and reduction in radio interference at the same time.

You really are not trying to protect different track busses from each other. The goal is to protect low powered throttle bus lines or other signaling lines from the higher powered track buss. Twisting the track buss wires cuts down dramatically on the amount of interference they put out (or absorb). Putting all of the twisted track buss wires in a conduit or a bundle is fine, however, run the Throttle bus separately.

[edit] Terminating bus wires

In general, bus wires should not need termination. However, you may find it beneficial on pre-installed long wire runs and/or in situations in which your experiencing control problems, decoders losing their programming or worse, decoder blowing up. Refer to the your system manual to see what is recommended.

[edit] Feeder Wires

Track soldered at the joints, with feeder wires

Feeder wires are wires that connect the track to the bus. That is, every few feet, a set of wires runs from the main bus to the track. The goal is to make sure that there are no voltage drops and that the train has full power available to it. The benefits are that the train will not slow down. Also, this helps to ensure that the booster's short circuit protection will work.

[edit] Feeder Spacing

For a trouble-free railroad, it's recommended that you follow these guidelines for feeder wire spacing.

[edit] Feeder Tips

[edit] Don't Place Feeders at the end of a short section

If you have a very short block or track section, and will only have one set of feeders, place it in the middle instead of at either end. Don't worry if you can't get it exactly in the middle. There is the ideal and then there is the practical: aim for the ideal, but keep the practical in sight.

[edit] Wire type for outdoor use

A discussion on the various types of wire available.

• Direct burial
  • Avoid - Not suitable for garden railroad use.
• Underground sprinkler wire
  • Avoid - Solid wire, but much too small in diameter to carry the necessary currents.
• Low voltage lighting wire
  • Avoid - Intented to be terminated inside above ground lighting fixture. Stripping stranded wire and then trying to solder buried feeders to it will eventually fail, even if the connection has been waterproofed. The problem is that soldering stranded wire makes it very rigid and the tiny flexible strands can break off. For garden railroads, walking on buried wires aggravates this problem. If connection is not waterproofed, then the wire is doomed to fail.
• Buriable "Romex:"
  • Avoid - This wire, available in the United States, has a jacket that makes the wire buriable. However, once you cut into this jacket, it's no longer waterproof and nullifies the jacket's benefit.
• Heavy solid wire.
  • GOOD - The fatter the wire, the longer it will be before it corrodes through. We can't tell you how many years, but solid should give you plenty of time.
  • For garden railroading, another thing that to consider is the wire's mechanical strength. In short, the thicker it is, the better at knowing it's there sooner with your shovel.

[edit] Detection Blocks

Main article: Block detection

Block detection is a method for detecting rolling stock within a given section of track with the use of stationary decoders.

[edit] Reverse sections

Main article: Reverse sections

See also: Turntables

Although the electrical polarity on the rail does not control the direction of the loco, you still have to deal with reverse sections on your layout. If the track turns around back onto itself, the right rail will come in contact with the left rail which will cause a short circuit; the same as placing a metal object across the rails.

[edit] Troubleshooting

[edit] Notes

[edit] Bi-Color LED's as Track Indicators

A bicolor LED can be hooked up as indicators around the layout is a convenient way to see the power status of sections of the layout. The LED indicates whether a track section is powered up, if "Zero-stretching" Analog mode is being used and its local direction, and can even be used to indicate if the GAPS in a reverse section are matched or not.

You will need:

• One 2 lead bi-color LED Radio Shack #276-012 (Or any cheaper 2 lead bi-color LED will work)
• One 1K ohm, 1/4 watt resistor (Radio Shack #271-1321)

Connect the 1K resistor in series with either one of the LED leads to make a "ballasted" LED (current limited). With the 2 leaded bi-color LED there is no strict polarity to observe, the emitted color depends on the direction the LED leads are connected to the track. If you plan on using zero-stretching, it's recommended that you connect neighboring sections with the same polarity so the LED will be of consistant color.

Simply connect the "ballasted" led across the track to indicate the track is powered. If you connect a "ballasted" led across one of the double gaps of a reverse section the LED will be OFF (un-lit) when the gap polarity is matched.

[edit] See Also

• How to safely wire a programming track
• Wiring for garden railroads
• Wiring large layouts

Move on to read about track work.