Many potential railway modelers will be prepared, when the time comes, to lay track, install points and scenic their layouts. What they are less inclined to do is wiring. We are raised with the idea that electricity is dangerous - and it is. However, so is driving a car, but that doesn't seem to stop most of us from doing it. There is also the notion that layout wiring is complicated and if you stuff it up it could be not only costly, but you could get blown up in the process. This article is designed to allay some of those fears and provide some basic information for those who want to do their own layout wiring.

Basic Physics
Energy - of which electricity is a form - cannot be created or destroyed, only changed. Electricity is natural as you find if you watch a storm and see the lightning. When lightning is generated in the atmosphere it eventually reaches a point when it "overflows" - it discharges to earth with the characteristic flash that makes watching it so exciting. Just as electricity is generated in the atmosphere during storm activity, machines called generators can also excite electron flow in suitable materials called 'conductors'. Most metals are good conductors, such as aluminium, copper, brass and so on. Conversely, some materials like dry wood, plastics and rubber are not. They are called 'insulators.' Conductors do not inhibit the flow of electrons, but insulators do. However, even the most efficient conductors like copper and aluminium offer resistance to electron flow. This means that the pressure must be increased to push the electrons along the conductor. This causes effects that we can and do utilize. For instance, if the resistance is fairly low, we get heat. If it is high, we get light. (This also assumes that the material offering the resistance is suitable, but let's keep it simple.) The third effect is electro-magnetism. Three common examples of these effects are: a heating element of an electric fire; an electric lamp and an electric motor.

In the 18th and 19th centuries the early experimenters with electricity worked out the relationship between the 'pushing force' - pressure, the resistance to flow and the by-product of pressure against resistance - current. Three of these experimenters gave their names to the three most common units of electricity in everyday use: Volta, Ampere and Ohm. Ohm was responsible for "Ohm's Law" which shows the relationship between Volts, Amps and Ohms. (This: ? is the symbol for Ohms.) Another unit of electrical power is Watts. Lamps are rated in Watts: 40, 60, 100 etc. For example if the voltage in a circuit is 240 Volts and the wattage of a lamp is 100, then the current in Amperes may be calculated using the formula I (current) = Watts (W) divided by the voltage, or I=W/V. Or 100/240 = 0.41 Amps. The diagrams below illustrate this idea. (Figures 1 & 2)

Resistance may be used to reduce voltage, so a volume control on a radio and a voltage controller on a model railway use the same principle - one reduces or increases the sound, the other does the same with loco. speed. It may also be used if you want to put LED's in a circuit. Putting 12 volts across a 2 Watt LED will blow it, but a resistor in line (in 'series') with it will reduce the voltage to the point where it will glow without blowing up. In effect, the controller on your railway is a variable resistor: sliding it up or down (or turning it forward or backward) varies the resistance and allows the train to go faster (higher voltage) or slower, because in DC motors the speed is controlled by the voltage applied.

Electrics for Modelling
In many countries such as Australia, domestic voltage is 240 Volts AC. AC stand for 'Alternating Current'. Its opposite is DC: Direct Current. Without getting too technical (you can drive a car without knowing how an internal combustion engine works) it is possible to convert AC voltage to DC and to raise it or lower voltage through the principle of electromagnetism in a transformer. When you go to the model shop and buy a train controller, usually its primary voltage is 240 AC. Inside the controller the voltage is reduced to 12Volts and changed from AC to DC. Most model railways use 12Volts DC. It is safe and efficient, even for children. Because of this very low voltage and the smallness of the motors in model locomotives, we need not concern ourselves with either Amperes (because they will be extremely low) or Ohms, or Watts, but voltage is important because it allows us to run trains at varying speeds. Additionally, when using DC voltage a change of polarity (positive and negative) changes the direction that a DC motor (and thus the loco.) runs, as the diagram below indicates. (Most controllers have a change of direction switch built into them.)

In the diagram above it is assumed that the voltage to the track is a nominal 12 DC. A locomotive placed on this circuit and would run clockwise with the connections in the top diagram and in the opposite direction if the connections were reversed. This is known as changing polarity. Polarity becomes very important (and complicated) if you use live frog points, such as Peco Electrofrog. This is because when the point changes the polarity of the frog changes, because the point blade carries the voltage and is the contact point for it. However, Insulfrog (plastic frog) points are not a problem. What is a problem with voltage is how many locos are running at the same time on the same track.

Think of electricity in a cable like water in a pipe. The transformer/controller is the tap. Assume that the pressure in the pipe - determined by how open the tap is - is not changed once the tap is turned on. Now also assume that along the pipe are 3 smaller taps numbered 1, 2 & 3. (Three locos.) Open tap 1 and the flow will be at the same pressure as the main tap. Now open tap 2 at the same time. The pressure at taps 1 and 2 will fall because they will be getting half the main pressure each. Open tap 3 and it will drop again because they are each taking a third and so on. If this was locos. on a track you'd be lucky if there was any movement at all from any of the locos. It should be noted here that DCC control solves this problem. But what is the solution to this problem if you don't use DCC because of cost etc.?

In the diagram above the voltage from the controller (red +) is fed to four switches at the same time. This is known as 'in parallel'. Because of this the voltage at each of the 4 block switches is the same. At 4 different places the positive track has been cut such that there is a gap that has created an 'open circuit'. From each of the 4 pieces of track a 'dropper' cable has been soldered to the track and taken to the other terminal on each block switch. Notice that the negative track has not been cut. This is known as a 'common return' because it is shared between all four blocks. This method allows the following: 1: each block is isolated from the next as long as the switches are off. This means that a train on block 1 can only run as far as the gap. It may only continue if block switch 2 is on and the same is true for all blocks. 2. All blocks may have locos. running on them at the same time with no loss of voltage. 3. The block system is prototypical for train control. The train may only proceed through the next block if the signal that controls it is in the 'clear' position.

Copyright © Peter J.Baddeley 2005