The electrical side of model railways can seem too complex for anyone not familiar with the workings of electricity. Many modellers can end up with a rat's nest of wiring under their layouts. But for basic layouts, it's not at all difficult.

The most common standard of wiring for model railways uses 12 volt direct current. This uses a controller that varies the voltage to the track to control the speed of the train. Changing the polarity (+ and -) the train can be made to change direction.

Today DCC (digital command control) is an increasingly popular method of control which simplifies wiring.

DC systems.

To start with a simple circuit, there are just 2 wires from the controller to the track. Most transformer / controllers (power packs) have 4 terminals. One pair is usually marked DC, 12V DC VARIABLE or CONTROLLED or TO TRACK. The other AC, 16V AC or ACCESSORIES.

This is pretty straightforward, and instructions in the train set should cover this anyway. The important thing to remember is never to connect AC to the track. If you do, your locomotive will probably hum or shudder. The motor will be trying to go both ways at once. This is obviously impossible, and if left this way more than a few seconds may damage the motor beyond repair.
 

Above: AC and DC outputs on a typical model railway power pack.
This one uses quick connect terminals. Others may plug in or use screws.

The other end of the wires usually go to a socket, terminal or other device on the rails or clipped onto a section of track. 

The majority of model railways operate on 12 volt DC (Direct Current). The 16 volt AC (Alternating Current) on many train transformers is intended for accessories like remote controlled points (the junction tracks), signals or lighting in model houses or streets. If you are going to operate more than a few of these, you will usually need to invest in a separate transformer to power them, as the more you have operating, the less power you have left to run the trains. You may find your power supply being constantly overloaded. In most cases, this trips a thermal overload switch that will shut down the power to protect the transformer. Usually these need a few minutes to cool down before resetting.
Some controllers use a fuse, but these are rare nowadays.

Generally the controller provided in a train set has sufficient power to run one or two trains and little, if anything else. Extra track can be added to your set and the same controller will have no problems with this. It's not the track that draws power, it is the trains and electrical accessories.

If you want to run two trains at once, the simplest method is to build a second track circuit. This usually takes the form of converting the single track to double track. One controller is connected to the outside track and another to the inside track. Effectively two separate train sets, one inside the other.

The "problems" really begin when you wish to run more than one train on one track or if you have double track, to run trains from one to the other without difficulty. Also if you intentionally or unintentionally put a reverse loop into your track plan. That is, if you have a track arrangement where a train can turn around and run back in the opposite direction along the same track. Without special wiring and insulated joins, you will get a short circuit and the train will not run. Further, the fuse or thermal cut-out in your controller will shut off power to the track to prevent damage to the transformer.

To control several trains on one layout with DC is not difficult in itself. But it does require some special wiring. This subject is covered by a number of books available on wiring a layout and shall not be covered here. We are happy to assist you with solving such problems when visiting the shop. Most are not too difficult to explain verbally or on paper.

DCC systems.

The other increasingly popular standard is known as DCC. This stands for Digital Command Control.  With DCC, the speed and direction of the train is controlled from within the locomotive itself instead from the voltage on the rails. Each locomotive has a digital decoder installed which is programmed to have a unique address (or number). A digital command station (DCC controller) sends a coded command along the rails. Only the locomotive the command is addressed to will respond. It is therefore possible to have several trains on the layout all individually controlled without complicated wiring and isolating switches everywhere. Recently the price of entry-level DCC items have come down in price to the point where a basic DCC system is no more expensive than a good quality DC controller. Given that you won't need so much wiring, isolating sections and switches, it could actually work out cheaper in some cases.

See our DCC products page.

Page updated 05/01/2009.