2 rail or 3 rail track

[Alex H]

Hi.  

 

Am switching up from n-gauge to HO/OO and have started to come across 3 rail track systems.   I have tried googling and reading different articles but am still not sure I understand it.  Can kind person explain in simple terms the benefits and disadvantages to 3 rail these days.  

 

I am setting up a new DCC powered HO/OO layout which will be based on German rolling stock from era I and II (these tend to be smaller which will suit my restricted space).  I imagine that most of the rolling stock will be new although there may be some bought second hand.  My grandson also has two locos already a Hornby Flyings Scotsman and a Thomas, both of which I will get DCC'd and he will want to run them on the layout.

 

If I understand it correctly, and probably don't, you can run 3 rail locos on a 2 rail system but not the other way around.  if that's right, does that mean that the two locos my grandson has wont run?  However I am not sure what the advantages are over the other and would v very much appreciate some help in getting this basic question resolved, so I know what track to get.

 

Thanks

 

 

 

 

[Nearholmer]

Three-rail is a strictly ‘retro’ system, so unless you are into retro models, or Maerklin H0, which still uses a form of it, not really the thing. I am into it, in 0, because I run a fair proportion of pre-1960 trains, and you will find a lot of Hornby Dublo collectors/runners using retro three-rail in 00.

 

Wiring three-rail is marginally simpler than two-rail, but not really decisively so.

 

Locos are “one or the other”, unless wired for and switched for “either/or”, which I’ve never seen in 00.

 

Rolling stock for three-rail only use has non-insulated wheels, so will short-out two-rail, but the vast majority of post-1958(ish) r-t-r stock has wheels that are insulated, so can run on either.

 

Starting out in 00, unless collecting old stuff or Maerklin, go two-rail; it’s the de-facto standard.

 

 

Edited February 21, 2021 by Nearholmer

[Chimer]

You can't run 2-rail locos on a 3-rail system or vice versa.  A 3-rail loco picks up power from the third (central) rail and returns it via the motor to both the outside rails (or vice versa).  So it can't run on 2 rails, there isn't an electrical circuit through the motor.  A 2-rail loco picks up from one rail and returns to the other.  On a 3-rail system the outside rails have the same polarity, so when you put the 2-rail loco on 3-rail track, once again you don't have a circuit.

 

The one thing you can do easily with 3-rail that you can't with 2-rail is reverse loops, as the outside rails have the same polarity from the start.  The obvious disadvantage is the existence of the third rail itself (unless you're modelling London Transport which does have a central rail).  I believe Marklin (and very probably other continental manufacturers) have a sort-of third rail system with studs on the centre-line instead of the third continuous rail, which will look better.

 

And finally, I'm trying and failing to get my head around the possibility (or impossibility) of third-rail DCC.  I feel certain if I said "it can't be done", someone would be along in seconds to prove me wrong, but the idea doesn't seem to compute, really.

 

Cheers, Chris

[Alex H]

Thanks very much both.   I will stick with the two rail track !!   Now just need to decide which one.

I guess Peco is the one that most people use.  Have you had any experience with Trix C ?  I an just thinking that it might stand up better to grandchildren.

 

Thanks again

 

Alex

[Nearholmer]

31 minutes ago, Chimer said:

feel certain if I said "it can't be done", someone would be along in seconds to prove me wrong, but the idea doesn't seem to compute, really.

It can be done. Trust me.

[Zomboid]

You can run trains with on board batteries on 2 and 3 trail track equally successfully...

[Nearholmer]

Or, on no track at all.

 

But that possibly isn’t the OP’s intent.

[john new]

3 hours ago, Alex H said:

Hi.  

 

Am switching up from n-gauge to HO/OO and have started to come across 3 rail track systems.   I have tried googling and reading different articles but am still not sure I understand it.  Can kind person explain in simple terms the benefits and disadvantages to 3 rail these days.  

 

I am setting up a new DCC powered HO/OO layout which will be based on German rolling stock from era I and II (these tend to be smaller which will suit my restricted space).  I imagine that most of the rolling stock will be new although there may be some bought second hand.  My grandson also has two locos already a Hornby Flyings Scotsman and a Thomas, both of which I will get DCC'd and he will want to run them on the layout.

 

If I understand it correctly, and probably don't, you can run 3 rail locos on a 2 rail system but not the other way around.  if that's right, does that mean that the two locos my grandson has wont run?  However I am not sure what the advantages are over the other and would v very much appreciate some help in getting this basic question resolved, so I know what track to get.

 

Thanks

 

 

These are the three main systems* with my assessment of their rating for simplicity. (Easiest first)

 

As an owner of obsolete Hornby Dublo I can state that centre rail three-rail with outside rails bonded together is by far the easiest to wire and run. That said it is now a system that has been obsolete for UK prototypes since the 1960s. Available second-hand and unless you want to buy a collectable rarity probably cheaper than comparable modern two-rail. Avoid Trix-Twin, it was an AC 3-rail system and a definite blind-alley. (Trix though did standard two-rail later). Parts and repair services are available via the HRCA Club. Unless you specifically like the "classic" model train era, and the look of HD tinplate track,  probably best avoided even allowing for the extreme simplicity of 3-rail wiring.

 

Modern 2-rail 12V analogue DC has a long pedigree with a lot of second-hand available, although not as detailed as the latest offerings these older models can let you build a collection cost-effectively. Analogue wiring can be complex for a largish layout but does not have to be.

 

DCC - I use it, but am a relative beginner. Some aspects are undoubtedly simpler in theory than analogue (DC) but other aspects are waaaaay more complicated with the adjustable settings and options for electronic control of extras like points and signals. If you pick DCC it will also to some extent restrict which locomotives you buy and run. However, I think it is fair to say that this is the long term direction for the hobby. If you are starting from scratch a small DCC installation is likely to be a wise move. By starting with DCC you avoid future conversion costs. A DCC loco, with the correct data/CV setting, can be run on analogue, but not the converse. I would take advice too on which control system will suit you as they vary from very basic (IIRC the Hornby Elite bundled with their starter train sets) upwards. I have a Bachman E-Z and an NEC Power Cab, both work but the latter has far more functionality. 

 

Just my opinion, and others may well have different views, but hope it helps.

 

* others exist but are rarer. (Outside 3rd, stud, IIRC Märklin AC?, three rail but running rails separate etc. Even live O/head on two rail track - early Tri-Ang electrics.

 

Edited February 21, 2021 by john new
Updated the * footnote.

[sncf231e]

2 hours ago, Chimer said:

You can't run 2-rail locos on a 3-rail system or vice versa. 

 

And finally, I'm trying and failing to get my head around the possibility (or impossibility) of third-rail DCC.  I feel certain if I said "it can't be done", someone would be along in seconds to prove me wrong, but the idea doesn't seem to compute, really.

 

Cheers, Chris

Of course you can run a 2-rail locomotive on a 3-rail system; I do it often. Of course the running rails of the 3-rail system should be electrically separated like e.g. the Trix TTR system and many 0 gauge track systems.

Further, I run DCC on my 3-rail system in the garden and on my Märklin 3-rail system in the house without problems.

 

Regards

Fred

[john new]

2 hours ago, Nearholmer said:

Three-rail is a strictly ‘retro’ system, so unless you are into retro models, or Maerklin H0, which still uses a form of it, not really the thing. I am into it, in 0, because I run a fair proportion of pre-1960 trains, and you will find a lot of Hornby Dublo collectors/runners using retro three-rail in 00.

 

Wiring three-rail is marginally simpler than two-rail, but not really decisively so.

 

Locos are “one or the other”, unless wired for and switched for “either/or”, which I’ve never seen in 00.

 

... snipped...

 

 

The one item that was wired that way, and I still have an example, were the older Tri-Ang o/h electrics. They had metal pantographs and a sliding switch on the roof so could be 2-rail track powered or O/H live with track return on one side ony. Mine is the WCML E6001. I did have two of the EM2s, long sold on, that were, IIRC, similar. A feature lacking in their more recent models that I understand have all plastic pantographs. Is that progress?

 

Edited February 21, 2021 by john new
Typo

[BR60103]

The operation of locomotives is different on DC between 2 and 3 rail.

On 2 rail, the controller selects the direction of the track, either running to the right or the left (or Clockwise / CCW on a loop).

On 3 rail, the loco runs either forward or backward relative to itself.  This allows head on collisions or two locomotives trying to rip their tenders apart. 

 

Brand of track: Code 100 is generally compatible (what you find in sets plus Peco) unless you buy the ones moulded on roadbed (e.g. Bachmann EZ track). Code 75 and bullhead need special consideration.  Older track may not be compatible as rails were larger.

Marklin is a rule unto itself.

 

[Kris]

14 hours ago, Alex H said:

Thanks very much both.   I will stick with the two rail track !!   Now just need to decide which one.

I guess Peco is the one that most people use.  Have you had any experience with Trix C ?  I an just thinking that it might stand up better to grandchildren.

 

Thanks again

 

Alex

 

If the track is fixed to a board then Peco is fine for children to use, if not fixed to a board i.e. laid fresh on each occasion then the connectors between the track can (and do) work loose causing lots of frustrations. 

[TonyMay]

Usually newcomers are concerned abuot DC v DCC, not 2-rail v 3-rail.

[Nearholmer]

Probably a function of being interested in early German stock, which Maerklin tends to provide.

[Chimer]

16 hours ago, Chimer said:

You can't run 2-rail locos on a 3-rail system or vice versa.  A 3-rail loco picks up power from the third (central) rail and returns it via the motor to both the outside rails (or vice versa).  So it can't run on 2 rails, there isn't an electrical circuit through the motor.  A 2-rail loco picks up from one rail and returns to the other.  On a 3-rail system the outside rails have the same polarity, so when you put the 2-rail loco on 3-rail track, once again you don't have a circuit.

 

And finally, I'm trying and failing to get my head around the possibility (or impossibility) of third-rail DCC.  I feel certain if I said "it can't be done", someone would be along in seconds to prove me wrong, but the idea doesn't seem to compute, really.

 

Cheers, Chris

 

Mea culpa, my bad, sorry .  I was really only thinking about Hornby-Dublo 3-rail.  I recall now that I did think about Trix Twin back then, as one way of controlling two trains on the same track, so must have realised the running rails were electrically separated - wiring a return loop must have been even more fraught than with standard two-rail.  And of course my brain has now realised that there's no reason why DCC magic can't be added to a system with a centre rail pickup.  At least I got the highlighted bit right ......

Edited February 22, 2021 by Chimer

[DCB]

DCC and 3 rail is an obvious match.   They both select whether a loco goes forwards or backwards, rather than left or right, and generally 3 rail is effectively live frog.  3 rail pickup is also  generally far better than 2 rail .   indeed most early 2 rail had to be live frog to equal the running of the 3 rail.    The problem with 3 rail comes with the detail.   Hornby Dubllo 3 rail has the two running rails electrically bonded but the points have an insulated rail between the blade and the frog.  That rail is hit by the centre pick up as the loco crosses the point so has to be insulated. The blade is also not designed to make contact so there is a more or less dead section for 2" or more on one side, that will cause most locos with one side insulated to stop dead.  This is a common issue with converted Triang locos unless the insulated wheel  pick up wire is shorted to the chassis

Other makes have different systems, Trix Twin has all three rails insulated, but many 3 rail locos have contacts which slide along the rails instead of wheel back contacts.  Much early 2 rail also had these sliders, Grafar and Roxex with their early Princess. Its quite an experience to see the way these crude early 50's models run, low speed's not great but they don't stutter like Oxford, Kernow etc and they actually stay on the track, even when it changes from kitchen floor to dining room carpet...

 

 

 

 

 

 

Edited February 23, 2021 by DavidCBroad

[Grovenor]

Since Alex said in his first post that he is modelling German then the options are only two, Maerklin (3rail studs) or the rest (2 rail).

Maerklin has long had the policy of being different so that buyers of Maerklin are locked in. Traditionally Maerklin was AC when the rest are DC. Nowadays Maerklin is mostly DCC but their own variant, not the standard DCC. Although there are a few other makers offering Maerklin compatible stock rhe real choice is to go with Maerklin or use 2 rail and have a wide choice of suppliers. And note that Maerklin own Trix and offer some of their models for 2 rail under the Trix brand.