Basic Electrical Terms for Model Trains

A train on a track next to a transformer

Ryan C Kunkle

You don't need to be an electrical engineer to build a model railroad. Still, a basic understanding of electricity and how it works will make it much easier to understand, especially when things don't go as planned.

These are some basic terms you'll probably encounter as you build a model railroad. All of these properties "scale up" to real-world applications as well.​

  • 01 of 07

    Voltage (Volts)

    There are three basic units of measuring electricity, volts, amps, and watts. Voltage is a measure of the force of the electricity. An often used analogy compares electricity to a water pipe. In this analogy, voltage is often used to describe the diameter of the pipe.

    In more technical terms, voltage is the potential difference between two conductors of the circuit.

    In most cases, Nominal Voltage is used as the designator, such as the 120 Volt circuits in home wiring. The actual voltage may vary slightly from this number, but not normally significantly enough to cause any issues with the appliances you use.

    Voltage is measured in Volts (V).

    Most model trains operate at between 10 and 18 Volts. The variable voltage is used to control trains conventionally with a transformer. Command Control systems use a constant voltage on the rails and control train speed differently. Lights and other accessories also normally operate at a fixed, or constant voltage.

  • 02 of 07

    Amperage (Amps)

    Amperage, measured in Amps (A) is the "Amount" of power in an electrical charge. In the water pipe analogy, Amps is the volume of water flowing through the pipe.

    Amperage is important to how many trains and accessories you can run. The more Amps your power supply puts out, the more you can do with it.

  • 03 of 07

    Wattage (Watts)

    A train on a track next to a transformer

    Ryan C Kunkle

    Wattage is a total measure of the work which the electricity can perform. Watts are equal to Volts multiplied by Amps.

    Typically, you'll see model train transformers measured in Watts. A 180 Watt transformer typically produces 10 Amps at 18 Volts. Since the voltage requirements of model trains of a similar scale are usually the same, the biggest difference between small and large transformers is the amount of amperage they produce.

  • 04 of 07

    Resistance (Ohms)

    The insides of a model train

    Ryan C Kunkle

    Electrical resistance, measured in Ohms, is just as it sounds—a resistance or inhibitor to the flow of electricity. Ohm's Law describes the relationship of resistance to voltage and amperage as Voltage equal to the product of Amperage times Resistance.

    Resistance is an important part of model railroading circuits. The most obvious electrical component associated with Resistance is the resistor, but diodes and other devices have resistance as well.

    On prototype trains, resistance is what makes dynamic brakes work.

    Continue to 5 of 7 below.
  • 05 of 07

    Alternating Current (AC)

    A train on a 3 rail track

    Ryan C Kunkle

    In alternating current, the polarity of the electricity is changing rapidly from positive to negative. The rate of that switch is measured in Hertz. Because home electrical systems in western Europe and North America both use AC but at 50 vs. 60 Hertz, there are often compatibility issues between transformers.

    When using AC, one side of the circuit is "hot" and the other "Ground." 3 Rail O Gauge trains and some HO and other trains run on AC power. Many accessories are also run on AC.

  • 06 of 07

    Direct Current (DC)

    A wiring schematic

    Ryan C Kunkle

    With direct current, power flows in one direction only, from a positive to a negative polarity. Batteries are DC. Most HO and N scale trains are also DC, where one rail is positive and the other negative.

    With conventional DC control, reversing the polarity in the rails is what reverses the direction of the train. This is also why reversing tracks like loops, wyes and turntables can create a short circuit if they aren't properly insulated.

  • 07 of 07

    Series vs. Parallel Wiring

    Staging yard lights on a model train

    Ryan C Kunkle

    Wiring is series vs. in parallel is most commonly associated with lighting in model trains. In series, voltage is shared and divided amongst all of the elements. In parallel wiring, the total voltage is equal to the voltage of each component.