How Non-Derailing Turnouts Work

One of the advantages of trains that use a three-rail track system is the ability to use the third rail in clever electrical circuits. Under normal circumstances the center rail is used as the "hot" power of the electric train circuit while both outer rails serve as the "common" side of the circuit. However, when one of the outside rails is electrically isolated from the other it may be used as an electrical switch when the metal wheels of locomotives and cars complete an electrical connection to the isolated rail. A common use of this feature is the non-derailing turnout.

Finding Common Ground

A Lionel service diagram showing the internal wiring of
a #1122-E turnout.

Since the introduction of the #1122 turnout in 1952, all Lionel O27 remote turnouts have been pre-wired for non-derailing operation, and it was a feature in Lionel's Standard O turnouts long before then. The wiring schematic as seen to the left is still the standard in today's Lionel remote turnouts. The two outside rails serve as the common "ground" of the track circuit. The inside rails however are electrically isolated by the frog on one end and by an insulated fibre track pin on the other. 

When the metal wheels of a car or locomotive complete the circuit from the outside rail to the insulated inside rail the turnout throws in the direction of the train to avoid a possible derailment. This operation works only for trailing point maneuvers [from diverging route to single route]. Since these turnouts are wired to receive power directly from the track this operation occurs even when no turnout controller is present. One should be certain that a train does not sit for long periods of time on these activation rails as continuous use may burn out the switch motor.

Other Uses

In addition to the safety of avoiding unnecessary derailments, the electrical properties of non-derailing turnouts can be used for other purposes as well. In the example on the left two turnouts are wired together so that they throw simultaneously either with a switch controller or by train activation by connecting the electrical posts controlling switch motor movement to one another. 

If connected together identically, throwing one turnout will result in identical motion from the other turnout. In this scenario one can select either Track A or Track B by simply throwing one turnout and the other will snap to a safe exit automatically.

For a bit more excitement the turnouts can be connected opposite one another so that when one turnout throws straight the other goes to curve. Looking at the diagram above, a train traveling from the top of the track layout reaches a curved turnout at the right side of Track A. Initially the passing of the train activates the opposite switch to throw straight for Track B. However the arrival of the train at the left turnout throws it safely back to the train on Track A and simultaneously throws the right switch to straight toward Track B. After completing the loop the train now finds the right turnout thrown towards Track B and its exit on the left side returns the right turnout to Track A for the next loop. In this way the train continuously and automatically switches between the two options on each loop.

Once this concept is understood it may be used for a variety of purposed in various track designs. The uses are limited only by your imagination! Layout visitors will be astonished at how the train automatically changes routes with no operator input. 

Happy Railroading!