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On a prewar 072 switch, the rails that activate the non-derailing feature are insulated and closer to the switch.   This design was not used later.   This picture shows the non-derailing pickup on a prewar 711.

There  is a problem with this non-derailer design.  The engine and cars center pickups cross the ACTIVE non-derailing contact rail. This can trigger the switch when not desired causing a de-railment.  When going straight the center pickup momentarily contact the turn non-derailing rail.  When turning the center pickup momentarily contacts the straight non-derailing rail.

If there is only one pickup on a car, it may act like a ground and throw the switch the other way with a car or engine on the track.  The same will happen when one of the 2 pickups on an engine does not make good contact.

When using a postwar switch motor and the power tap for constant voltage, running the engine slow in conventional mode will have a large voltage difference and it may throw the switch causing a de-rail.

I have seen this derailing with these switches in use.   It doesn't always happen with engines, but one out of 50 times is too much.

What I suggest is to disconnect the wires from these non-derailing pickups and leave the rails insulated and inert similar to postwar switches. Then the 2 tracks after the switch have an outer, insulated rail. The insulated rails will need insulation pins on both ends to function correctly. Then a wire from the insulated track to to the corresponding left or right post on the switch motor. You now have a more up to date non-derailing contact.  The center pickup never touches the non-derailing rail to cause problems.

Simple schematic of adding 2 tracks with insulated rails for non-derailing.

If it works bacwards, just switch the wires on the switch.


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Thanks for the interesting discussion of the non derailing feature of the early 0-72 switch. I have always avoided the early version and look for the later prewar O-72 switch with the large plastic frog. This version does a better job of separating the center rail power from the outside rail power. It also puts the non derailing rails where they are on the O-22 switch.  The later switches may have a bigger problem with loss of power or ground on short wheel base locos, but Lionel attempted to address this with tender rollers and jumpers to the loco.  

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