Wiring A Basic DC Layout


When expanding any train set or small oval/circle of track as we are doing here there are some electrical principals to keep in mind. The first, speaking electrically, is that the rails are simply extensions of the wire coming from the power pack to the electrical motor in the engine.

The second thing you will want to set up during your wiring is what is called the right hand rule. This simply means that when you view your layout from the power pack and with the direction switch pushed or turned to the right, the engine travels the track in a counterclockwise direction, to your right.

Once you have the wires connected between the power pack and the rail to cause this direction of travel the outside rail is the positive (+) rail and the inside rail is the negative (-) rail. All two rail model railroad engines operated on DC (Direct Current) thus the use of the terms positive and negative.


You will need to be sure that any additional feeders to your layout are wired exactly the same or you will create a short circuit.
The best way to make sure you are correctly wiring your layout is to use wire with two different colors of insulating jacket.

We recommend the use of doorbell wire for any additional track wiring. Normally doorbell wire comes in small coils, in 25 to 50 foot coils, and with a red and a white insulating jacket. Use the red jacketed wire for your positive wire to the outside rail and the white for the negative wire to the inside rail. Also, doorbell wire is normally #18 US Wire Gauge wire which will handle any current draw on a model railroad. Common telephone wire can be to small to handle the current draw of even a small layout such as we are working with here depending on how many engines you decide to use at one time in the future.
There are several ways of connecting wires to the rail of a model railroad. The very best way is to solder the feeder wire to the outside of the rail as this makes the most positive electrical connection. However, there are several things to be taken into account when soldering wire directly to the rail and since this is just a basic layout we won't go into that until a major expansion.

We suggest you visit your local hobby shop and purchase two sets of rail joiners that have the wires already attached. Or, if you have soldering equipment already available, you can simple make these up yourself by soldering the wire to the bottom of a rail joiner. The latter is preferred because you will be able to color code the rail joiners with the wire and now which one will need to be placed on the outside rail and which one goes to the inside rail.

Many of the commercial pre-wired sets of rail joiners use the same color of wire on each joiner making it a little more difficult to figure out which rail joiner goes to which rail with out causing a short

On this particular layout we suggest you put one set of feeders at the top of the dogleg and another set in the middle of the straight track directly across from the first set in the straight sections of track. Even if this layout is only going to be what you want to build and you don't want to expand it, we suggest you purchase an 8 place terminal block to connect all of the wiring to and not double wires up on the terminals of your power pack.
The reason for this is all power packs vibrate from the AC current used in the transformer part of the power pack. This vibration can cause your wires to come loose causing un-needed problems and destroying the fun of watching your train run.

To wire your feeders from the power pack to the terminal block simply strip back enough insulation on each wire so you can loop the wire from the first terminal screw of the positive half of the board to the second. Do the same for the negative wire. Then you can connect each set of track feeder wires to the screws opposite of the ones already used. This way no terminal screw has more than one wire connected to it.

Extended Wiring

As you can see from this drawing, we have expanded our basic track plan. We have added some turnouts and additional track to create a small yard, a passing siding and a couple of industrial sidings. All of the turnouts are #4 in size.

This expansion will allow you to take cars from the yard and switch them out to the industrial sidings plus picking up cars at these sidings and taking them back to the yard. The bottom track in the yard runs clear out to the edge of the plywood and is labeled "Interchange Track." This would be the track where your railroad interchanges with another.

You can shorten this track and just make it another yard track if so desired. These simple additions add more realism to operating your model railroad. The green lines on the drawing indicate a scenic divider that you can install if desired. A scenic divider does exactly what it says, divides the scene of one side of your railroad from the scene on the other side of your railroad.

For the purpose of these explanations, a "switch" is an electrical switch of one type or the other. A "turnout" is the term used for the device that switches your train from one track to another.
Bill of material:

5 - #4 Right Hand Turnouts

2 - #4 Left Hand Turnouts

20 – Straight sections of track (You may want to consider flex track here and cut it to the length you need.)

5 - Single Pole Double Throw Center Off Switches

1 - Single Pole Single Throw Switch

2 - 8 space terminal boards
If you only plan on having one train on this layout, you can eliminate the passing siding and put the turnouts in the mainline of your railroad. If you would like to run more than one train at a time, the passing track, some additional wiring and an additional power pack will be needed.
If you don't want to run two trains at a time but would like more than one engine on your layout without it running, some additional wiring will be necessary too. We will explain how to do both.
Before we start explaining the additional wiring, we suggest you take a look at our pages explaining DCC. While DCC is more expensive to start with, the wiring of your layout is much simpler as is any further expansions you may want to add later.
All of the additional electrical switches that will be mentioned here can be eliminated. And if you want to operate two trains at a time you will save the cost of additional power packs and all the wiring needed to control two trains at once. With DCC two trains can be run on the same layout in opposite directions without all of the switches needed to control them and memorizing the electrical blocks needed for multiple cab control. While DCC is more expensive initially it makes everything simpler and can be well worth the expense down the road.

If you are only going to ever use one train at a time on your layout, the wiring is as simple as the wiring for the basic track plan. Just add some additional feeders close to the end of the industrial spurs and to the spurs in the small switchyard. You are ready to go. If you want two engines, say one diesel and one steamer and want to store the unused engine on the layout, you will need to put an insulated rail joiner in the positive rail of one of the spur tracks, see red number (1) on the track plan. And then a simple on/off toggle switch into the feeder feeding the remaining positive rail in that particular spur.

We feel you will understand how to do this from the explanation on how to wire the layout for dual cab control. If you don't want to store the unused engine on the layout, then you will not have to add anything except the extra feeder wires. Remember that this is YOUR railroad and you can run it however you wan

The addition of the one insulated rail joiner and the one and off switch has caused the wiring of your layout to be called "common rail". The negative rail (-) is common at all points on the railroad and will remain so in the paragraphs that follow.
To Wire This Layout for Dual Cab Control
For dual cab control and the ability to run two trains on the layout at the same time you will first need two power packs. At this point we ask that you read the section on power packs and actually purchase two new ones. Save the old one, as there will be a use for it later on.
We recommend you call one of these power packs "Cab A" and the other "Cab B". Before proceeding, set both of these cabs up following the right hand rule and mark which terminal screw on the back of the power packs are the positive and negative terminals at that point.
Looking at the track plan you will also see there are six (6) more insulated rail joiners, shown in red on the negative rail side of the track, placed in specific locations around the layout. The placement of these six rail joiners divides the layout into 5 "blocks" which will all need individual feeder wires taken to the negative rail. For ease of wiring number each block from 1 to 5 as is done with the purple numbers.
To wire the layout you will also need five (5) single pole double throw (SPST) center off toggle switches. Be sure all of these switches are "center off" as you will need to turn the electricity off in these various blocks from time to time and not just switch from Cab A to Cab B.

There are one or two hobby manufacturers that make switches specifically for dual cab control. Your local hobby store owner can show you the different brands and sell you what you need. Or, you can purchase toggle type switches at electronic supply stores that work quite well and look a little more professional.

We do not recommend what is commonly called "sub-miniature" switches, as these switches will take quite a lot of use when you operate your model railroad and a more substantial switch will last a lot longer. Also be sure to check the electrical rating of the switches and purchase switches suitable for 3 to 5 amps of current draw.

We also recommend you purchase and install another eight position terminal board.

At this time you will also need to build some sort of control panel to mount all of the switches on so they will make sense to you. When you mount the switches into your terminal board you will have to decide which position you want the switch in for Cab A and Cab B operation.

For ease of explanation, we will tell you how to wire them so that when the toggle is in the up position you are using Cab A in that particular block. All the way down would them be feeding that same block from Cab B.

First take all of the wires loose from your first terminal board. Be sure to mark them in some way so you know where they went as you will be able to use them again as we continue. Next run a jumper wire from the first of the 5 terminal screws in one terminal block to the next. All terminal boards are divided, so this jumper should run from one to the next of 5 divisions on one side of the board or the other.

Mark these as "common" terminals. Then run a wire from the negative terminal of each power pack to one of the screws capturing the jumper wire. From the screws on the opposite side of the terminal board, run a wire to the common rail in each of your five blocks.

If you purchased toggle type switches you will need to do some soldering as most of these type switches on the market do not have screws to capture the wire.

First solder a wire on the center lug of the SPST for block one and connect the other end of that wire to your second terminal block in a partition marked (1).

Do the same for the remaining four switches. The reason for soldering these wires in place before the others is that it is just plain simpler than soldering them in place if two other wires are already hooked up.
Run a wire from the positive terminal of Cab A to one of the remaining 3 screws of your terminal block. Do the Same for Cab B. We recommend you leave a blank space in the terminal block for easier identification. Strip enough insulation off of a piece of wire and solder it to the bottom lug of each of the SPST switches and connect the other end to the screw on the terminal board marked Cab A.

(NOTE: The lugs of all SPST switches are always opposite the position of the toggle handle. Thus with the toggle up, the lug for that position is at the bottom of the switch.) Now do the same for Cab B which would connect to the top lug of the switch. Do not worry about having bare wire going from one switch to the other as long as it doesn't touch any other wire.

Mark the first 5 positions on your second terminal block and connect the wire from the center lug, the one you soldered in place first, from the switch for block one to the appropriate screw. Continue till you have all five switches connected to the proper positions on the terminal block.
Now take the positive wire that originally fed the track where block one is located and connect it to terminal position one. The wire that was run to the opposite side of the layout will connect to terminal space three. You will now need to run a new wire from switch 2 to the positive rail of block two and on around till the other two blocks have a feeder from their switches to the positive rail of the block.
You now have your layout wired for dual cab control and can run two trains at a time as long as the trains are never in the same block at any given point in time. You can even run the trains in the opposite direction with no problem as long as they aren't in the same block at the same time.

(NOTE: You may think that with trains running in the opposite direction would cause a short as you will have both positive and negative current running in the common rail/wire at the same time. This is not the case as all electricity returns to its own source. So the negative electrons from Cab A will not interfere with the positive electrons from Cab B as they are two separate sources.)