Wire N Scissor

This information is for Peco’s ElectroFrog crossover, which Peco calls a Scissors Crossing.

A double crossover has eight frogs. Four of them have polarity controlled by the points. The other four (2 sharp and 2 shallow) have track power feeders connected to them - these are the ones whose polarity you have to be concerned about.

There are several combinations of how the polarity might come to the ends of the crossover. If using DC analog train control, you’ll have to handle all this in the traditional way - with toggle switches. If using DCC, you can use a Digitrax Auto Reverser, one output of a Digitrax PM42, or a set of external contacts. This requires polarity to come into the crossover in a specific way and is what the rest of this dialog will address. First we’ll show you how it has to be, then we’ll discuss what you have to do to set your layout up for this.

Iillustration 1 below shows how polarity must come into the crossover — in parallel.

In Illustration 2, notice that the rails connecting to the crossover’s outside stock rails are of different polarity — the top one red and the bottom one green. Also note that the rails connecting to the sharp (blue) frog rails are different polarities. Connect one sharp frog feeder to one output of the auto-reverser and the other sharp frog to the other output of the auto-reverser. The shallow (yellow) frog feeders are connected directly to track power — the upper one to red polarity, the lower one to green polarity.

If using external contacts, instead of an auto-reverser, you have to realize that the contacts will be connected to only one throw bar, and that all throw bars must be operated as a set — that is, all four turnouts thrown for crossing over, or all four turnouts closed for going straight through. Of course, since a train can’t cross over at the same time a train is going straight, there’s no reason to not set your crossover up so all turnouts work together anyway.

Illustration 3 shows how to use a DPDT switch. This could be Peco contacts mounted on a Peco switch motor, a DPDT Cherry micro switch mounted to make contact with the throw bar, or any other common Double-Pole Double-Throw (DPDT) device or two Single Pole Double Throw (SPDT) devices. When the throw bar is one way, it feeds power from Rail A; when set the other way it feeds power from Rail B.

That’s all there is to making a Peco crossover work.

If the polarity doesn’t come into the crossover as shown in Illustration 2 above, you have a reverse section somewhere on the layout that hasn’t been resolved. To fix this, you need to go back on that track with the wrong polarity and install a reverse section so that the polarity comes into the crossover correctly.

Regardless of what the situation is, the polarity must match as shown in Illustration 2. Note that it doesn’t matter what the polarity is as long as it matches in all directions. Once it matches, resolve the frog polarity as described above.

You can also wire your N-Scale Scissor switch with Tortoise switch machines and toggle switches so that the auxiliary contacts on the Tortoise will route the power correctly and illuminate LEDs to indicate the Scissor switch position. See Illustration 4 below.