Besides the number of rails what is the difference between 2 rail and 3 rail systems? Will a 2 rail freight car run on 3 rail track? What about a 2 rail engine on 3 rail track?  I am still kind of new to this -- was HO for many years but now that I am older O scale is much easier to work with!! Thanks

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Dewman51 posted:

Besides the number of rails what is the difference between 2 rail and 3 rail systems?

The electrical power for 3-Rail trains is 18 to 20 Volts AC, while 2-Rail O-Scale is DC, just like your HO 2-Rail.

Will a 2 rail freight car run on 3 rail track?

Yes, if the track is more "scale-like" T section rails and good quality turnouts. Our 3-Rail Scale layout was all Atlas solid nickel silver 3-Rail track with broad curves, and we had LOTS of 2-Rail Scale freight cars. All locomotives and rolling stock were up-graded to Kadee couplers.

What about a 2 rail engine on 3 rail track? 

Sort of, yes. MTH offers many 2-Rail Scale diesels and steam models that are fairly easily converted from 2-Rail back to 3-Rail with the center rail power pick-up rollers.

I am still kind of new to this -- was HO for many years but now that I am older O scale is much easier to work with!! Thanks

 

The basic differences:

  • 2-rail layouts power the trains from the running rails through the wheels only. Therefore, the axles on all rolling stock must be insulated to prevent shorting the rails. The exception is lighted cars which provide a resistor load and "resistor axles" which are used for current-sensing detection.
  • 3-rail layouts power the trains from a center pickup roller providing the "hot" lead and "grounding" through BOTH running rails. The axles are typically NOT insulated.
  • Note that I didn't mention the control system. The reason is that the control systems are NOT dependent on the number of rails. If you wire it keeping your hot and ground consistent, it will work with the locomotives equipped with the proper decoders (obviously wired for the rail configuration).
  • I don't have a comment on track appearance as that's just a matter of personal taste. Generally, however, 3-rail trains are set up to handle sharper curves than 2-rail trains. To date, every 3-rail piece of equipment can run on O-72 curves (36" radius). Also remember that the "O" number on a 3-rail curve refers to the diameter and 2-rail curves are referred to by the radius. Larger equipment looks better on larger curves, so if you have the space, go for big curves.

As far as most rolling stock is concerned, there isn't much to prevent the use of 2-rail rolling stock on 3-rail layouts using "flat-top" rail such as Atlas, Gargraves, or MTH ScaleTrax subject to curve sizes. Because 2-rail rolling stock uses body-mounted couplers (Kadee, etc.), you must be conscientious of the length of the equipment as the longer equipment will require broader curves. O-72 curves are 36" radius which is considered sharp for scale-sized equipment with body-mounted couplers.

The other issue with 2-rail rolling stock is that the axles are insulated to prevent shorting out the power between the running rails. This isn't a problem on 3-rail track unless you're using insulated rails to trigger signals.

You can't use 3-rail rolling stock on a 2-rail layout. The flanges are too big and improperly spaced and the axles are NOT insulated. Thus they'll hang up on turnouts and short out the power.

2-rail locomotives are powered from the running rails, and with the exception of MTH "3-2" locomotives, can not be run on a 3-rail electrical setup. With the MTH engines (again subject to curve sizes and flat-top rail), they can be set up to run on 3-rail track. I do it all the time at the club (shameless plug: see my YouTube channel).

Hope this helps.

Matt Jackson
"The best service you can provide for the hobby is to pass on what you have learned."

 Angels Gate Hi-Railers San Pedro, California

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Two rail O SCale is identical electrically to HO.   Most O scale stuff requires a little more amperage than HO because of bigger motors, but not so much.    

Whatever control system you used in HO is the same in O Scale (as opposed to Lionel or MTH O Gauge 3 rail).   

Most HO control systems have no problem powering modern O Scale trains.

All the track issues are described above.    the biggest being the uninsulated wheels and large flanges generally on 3 rail equipment.    

So if y ou were HO at some point, you can do things exactly same in O Scale 2 Rail, nothing new to learn.

Modern control systems in both 2 rail and 3 rail using various command control may or may not be DC or straight AC on the rails since most carry coded control signel plus the power.

I have thought about this some more and came to a conclusion on the major difference.

The couplers, the curve radii, the electrical system, and even the flange size are generally different but are not show stoppers.

When you get right down to it, the major difference is that the 3 rail equipment axles are not insulated.     If you are using the rails for electrical pickup, this causes a dead short.     There is no short moving 2 rail cars to 3 rail track.

All the other differences can be worked around, or changed easily.

prrjim posted:

I have thought about this some more and came to a conclusion on the major difference.

The couplers, the curve radii, the electrical system, and even the flange size are generally different but are not show stoppers.

When you get right down to it, the major difference is that the 3 rail equipment axles are not insulated.     If you are using the rails for electrical pickup, this causes a dead short.     There is no short moving 2 rail cars to 3 rail track.

All the other differences can be worked around, or changed easily.

I would agree with that statement except for the LAST word. It's not easy (opinion) to 2 rail a 3 rail steam locomotive. There is also a  lot of TOY oriented 3 rail product.......anyone for a crayon car or a giraffe car? Yes, there is 3 rail stuff that is fairly easy to convert, and then there are some things that require a machinist's talents. There is quite a lot of 2 rail stuff out there on the secondary market. One thing for certain, you won't find everything that is out there in HO.

Simon

 

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