Bus Wiring for Model Railroads

Train set
onfilm / Getty Images

Whether your track has two rails or three, your trains are Z scale or G scale, your power is AC, DC, or if you use conventional or command control, even a modest-sized model railroad will run better if the power is supplied with a proper wiring bus and feeders.

Model railroad track supports and supplies the power to electric trains. But tracks have joints and these gaps are barriers to the electric current. A single rail joint, securely anchored with a joiner, will not cause a noticeable voltage drop. Multiplied over an entire layout, the cumulative voltage drop can cause your train to slow down or stall as it gets further from the power supply. If gaps are larger or rail joiners loose, the problem increases.

Power Supply

A common assumption when the train slows like this is that you need to buy a larger power supply. When choosing a transformer, the size of the track has much less to do with the size of the power supply than the number of trains and accessories you need to run. Proper wiring can save you a lot of money.

The solution is not to rely solely on the rails to carry the power over great distances. A pair of bus wires (one for each rail) run beneath the track will carry the current much more efficiently. In most cases, it is best if the bus follows the route of the track above so that the feeders can be kept short. If the design of your layout allows for some shortcuts, keeping the wire bus shorter can provide power and cost savings.

Smaller feeder wires connect the bus to the rails at regular intervals. Bus wiring is also a key step if you plan to run more than one train on your railroad at a time, no matter what system you choose. The bus can be easily separated to provide for separate electrical blocks.

Wire Size

Wire comes in many sizes or gauges. The smaller the gauge number, the larger the wire diameter. Wire also comes in solid and stranded varieties. The proper size and type of wire to use for a bus and feeders is a matter of some debate among modelers. Larger wires provide more current flow but are more expensive and harder to bend and solder.

Many manufacturers include recommendations in the set-up instructions for their control systems. It is always a good idea to follow those instructions. Often, terminals are designed for a specific size and type of wire. Most of our model trains are very low voltage and even lower amperage but you should still follow manufacturer's recommendations and take care when running your wires to avoid potential shock or fire hazards.

The length of the run required is also a key factor in determining a proper bus size. Shorter runs will experience less voltage drop and can employ smaller wire. Generally, No. 12 to No. 14 wire is ideal for bus wiring in most scales. For feeders, No. 18 to No. 24 can be used. Since the feeders must be attached to the rails directly, size is a factor in smaller scales.

How Many Feeders?

Ideally, there would be a feeder to every section of track on the railroad. Most manufacturers, however, recommend a feeder every six to twelve feet. If you solder rail joints, you can greatly reduce the number of feeders necessary.

In hard-to-reach areas, additional feeders are a good idea. Building redundancy by soldering joints and installing multiple feeders ensures that you'll always have power even if a wire breaks or a joint fails.

Soldering Connections

Even with a bus, there are still connections between the bus and feeders, feeders and rail, and additional breaks at control panels, power supplies, etc. Soldering these joints will help to minimize problems.

Joints in the rails can be soldered as well both for better power distribution and a smoother ride. Once soldered, shrink tubing, electrical tape or liquid electrical insulator should be applied over wire joints to prevent contact with other exposed wires and potential shorts.

Color Codes

Multiple colors of wire are available in just about every gauge and type. Color coding your wires makes maintenance much easier down the road. The colors you choose are up to you, but there are two ground rules that everyone should follow:

  1. Remain consistent.
  2. Take notes so you can remember what each color was for.

If you can't get all of the colors you need, colored tape and adhesive letter and number sets designed for wire can also be used to mark your lines.

Color coded wires
The Spruce / Ryan C. Kunkle