Making “The Switch” from 3 Rails to 2? What do you need to know?

If you have O Gauge trains and are considering switching to O Scale 2 Rail (OS2R) to get rid of the third rail, we recommend starting with this tutorial, then go check out the OS2R Product Guide™ to see what’s out there. OS2R will have you looking at the hobby from a new perspective!

The most important difference to take note of between 3-Rail and 2-Rail is the track and how electrical power pickups work. Understanding how the track works is vital in making the switch from 3-Rail to OS2R. To recap, 3-Rail trains run on AC power and is electrically set up such that the middle rail is your powered, or “positive” rail. Your O Gauge locomotives and lighted/animated rolling stock have a pickup roller underneath to pick up power from the center rail. The outer two rails are grounded, or “negative” rail. This means if you have a piece of metal (say, an all-metal wheelset) touching only the outer two rails, but not the center rail, you will not have a short. If you have a piece of metal touching the center rail and one of the outer rails, you will get a short.

OS2R trains can run on Straight DC, Digital Command Control or Dead Rail (Power Onboard Radio Control). Dead-rail is the name for battery powered models; the rails don’t need to be powered and are electrically dead, hence the name. For both DC and DCC, the electrical set up is such that the electrical circuit is a loop: one rail is powered and the opposite rail is grounded. This means the wheels of the locomotive and lighted rolling stock pickup power, not a dedicated roller. If a solid piece of metal (say, an all-metal O Gauge wheelset) touches both rails, you will get a short. How does one avoid this? Electrically insulated wheelsets. Below is a diagram of what an insulated wheelset looks like. The left side of the diagram shows a solid connection of the wheel and axel, while the right shows the axel separated from the wheel by an insulated bushing (typically plastic, though rubber can be used as well).

In OS2R, the modeler must familiarize themselves with insulated wheel sets. The wheels on most toy trains in O Gauge are made of solid metal. That is a good sign of quality, but that also means they are electrically conductive. When you place a 3-Rail wheel set on 2-Rail track and turn the power on, you will short out the track every time. This again, is because the wheels and axels are solid metal, which is conductive. Shorts are dangerous on your layout, and can damage your models, electrical equipment and scenery. Whenever you are converting a locomotive or piece of rolling stock to 2-Rail, make sure the insulated side of the wheelset is on the same side! This is especially important for trucks with metal side frames or cars/locomotives that pick-up power from the rails.

There are two kinds of insulated wheel sets. The first kind is a wheel set with one side insulated so that the other side will pick up power. This is displayed in the diagram above. Trucks with these kinds of wheel sets are what you will find on locomotives and powered/lighted rolling stock. On rolling stock needing power, one truck will pick up from the left rail, and the other will pick up from the right rail. The second kind is a wheel set that is totally insulated, where each wheel is insulted from the axel. In this kind of wheelset, both sides would have an insulated bushing and look like the right side of the diagram. You can find these on non-powered or lighted rolling stock. Trucks with these wheel sets in them can face any way since no electricity is transferred through the axel.

It is vital that you make sure each non-insulated wheel set is facing the same way in the truck, and that the entire truck picks up from the same rail. It is also vital to make sure the other truck does the same, and picks up from the opposite rail. Failure to do this means that you will have a short and your train won’t move.

Locomotives work a little differently. Most diesels work the same way a lighted passenger car or caboose will work: the front truck picks up from one rail, and the rear truck picks up from the other. Steam locomotives work such that the entire engine’s wheel base will pick up from one rail, while the tender trucks will pick up from the opposite rail. Multiple truck diesels and electrics will require you to consult the locomotive’s manual to see which truck picks up from which rail. If your locomotive does not have a manual, or you need help identifying something, members of the O Scale Forum will be more than happy to help you!

In OS2R, it is very common for those who model traction to use live overhead wires. A model pantograph or trolley pole picks up power from an overhead wire to power the motor.

Electrically, OS2R is very similar to HO Scale in that both use DC or DCC and run on two rails. While O Scale Central will produce OS2R specific electrical guides, HO Scale wiring guides will give you a good idea of how to get started and operate trains and wire a layout for DC or DCC. The NMRA Beginner’s Guide has a guide to setting up electronics. Though HO examples are used, the basics are the same for O Scale.

In switching from “Scale 3-Rail” to OS2R, the good news is if you like your rolling stock, you can use it! Rolling stock only needs trucks and couplers to convert to 2-Rail (often a very simple procedure). Sometimes, scale 3-Rail rolling stock already has holes tapped for Kadee coupler draft gear (MTH Premier and Atlas for example). Upper-end “Scale 3-Rail” locomotives that are more detailed tend to be selected for a full 2-Rail conversion. Locomotives will require some extensive modification, which can be a fun modeling project, but can also be intimidating the first time. Some people offer conversion services. To find vendors who do, please visit the OS2R Product Guide™.