Third rail (model rail)

Both the track and rolling stock were made from pressed, lithographed tinplate, with a few pieces of die-cast zinc or turned brass.

Using a two-rail electrification system for a model railway has a number of difficulties, for both track and rolling stock.

Pointwork was a further problem, as the frog and moving blades are connected to opposite rails, according to which direction in which the points are set.

A two-rail locomotive must both avoid shorting the two running rails, and must also collect current from both sides independently.

For two-rail, current collection is typically done by phosphor bronze spring strip collectors on the back of the wheel rims.

Three rail contact also negates the need for insulated wheels, an important consideration before plastics became widely available.

Three-rail DC locomotives will move in the same direction, 'forwards', whenever the third rail has the same polarity, no matter which way round they are placed on the track.

An accessory, such as a railway signal, can be wired to a section of track that has had one of its outer rails insulated (not grounded), either at the factory or by a hobbyist.

A passing train then grounds the insulated rail, completing the circuit and causing the accessory to operate.

Because of this feature, railroad cars intended for three-rail operation will not work on two-rail track unless their wheels are first insulated from each other.

Conversion of three-rail cars for two-rail operation, or vice versa, is thus a common practice among hobbyists.

Lionel tried to improve this situation in the late 1950s with its Super O track, which blackened the middle rail and made it thinner to reduce its visibility.

This system had the benefit of being more realistic by removing the central third rail common to O scale track, while retaining an effective power source.

As technology progressed, later developments in locomotive and track design would allow for two rail operation, and ultimately rendered the practice obsolete.