Railway Modelling

- Three-rail
Early electrical models used a three-rail system with the wheels resting on a metal track with metal sleepers that conducted power and a middle rail which provided power to a skid under the locomotive. This made sense at the time as models were metal and conductive. Modern plastics were not available and insulation was a problem. In addition the notion of accurate models had yet to evolve and toy trains and track were crude tinplate. A variation on the three-rail system, Trix Twin, allowed two trains to be independently controlled on one track, before the advent of Digital Command Control.
- Two-rail
As accuracy became important some systems adopted two-rail power in which the wheels were isolated and the rails carried the positive and negative supply or two sides of the AC supply.