O Gauge Trains Offer a World of Variety
O gauge trains are sometimes referred to as an O scale train, as often the terms scale and gauge are used interchangeably, but don’t let the serious modeler hear you do that. Scale and gauge have different meanings.
Scale vs. Gauge
Scale is the size of the model railroad cars and locomotives as compared to the real full-size version, which in O scale trains is 1/48.
Gauge, however, represents the distance between the outer rails of the track. For O gauge trains this is 1.25” or 31.75mm.
Gee, that was easy, but it’s about to get more complicated as there are many variations of O gauge.
If you created a circle using 8 standard curve O gauge tracks, it would measure 31” (787mm) in diameter. Now the fun starts because there are also gauges like O27, O36, O54, O72, and so on.
Simply put, the number is the curve size and tells you how large the diameter of the track is if laid out in a circle. O27 would mean the diameter is 27”, O54 would be 54”, etc. This is extremely important when deciding on space requirements and if railroad cars are compatible.
The chart below may give you a better idea of what I’m trying to say.
As you can see, the O27 gauge (E) has a smaller diameter and a tighter curve to it, while the O72 gauge (A) has a much wider curve which will take up more space.
Even though they are both O scale, a railroad car from an O72 set could not be used on an O27 layout as it would be too long to make the sharp curve and would derail. However, you could use an O27 railroad car on an O72 layout, if you wanted to.
2 Rail vs. 3 Rail Track
Besides the difference in track curvature, O gauge trains can also come in the two rail and three rail variety.
The two rail track looks and works like any of the other scales. These trains run on DC power which is distributed to the two rails. One rail gets the positive voltage (+) and the other one the negative (-).
I won’t get into DCC yet (Digital Command Control), which distributes power differently, because not everyone uses it (besides, it sounds like something from NASA).
The three rail tracks don’t look like real train tracks, plain and simple. Let’s face it… they actually have a third rail going right down the middle of the track. Nowadays, they try to camouflage the middle rail by making it black, it helps a little.
Instead of DC current it uses AC current, about 18 volts worth. The two outer rails in this system have the same polarity with the middle rail having the opposite polarity. Obviously, you need a specially designed locomotive to take advantage of that third rail.
So what happens if you put a 2 rail locomotive on a 3 rail layout? Nothing, the train won’t run. But if you put a 3 rail locomotive on a 2 rail layout something will happen, it will create a short circuit. Although the engines are not compatible all the other train cars are because they are not powered.
That third rail was always confusing to me as a kid as those were the tracks that came with my O27 Lionel trains. In a way it was kind of cool though, because all the other kids had the same old two rail tracks but my O gauge trains came with three rails.