outside rails use one or two?

Not sure what you mean, look at the cross tie on traditional track and you will see the two outside rails are connected with the middle rail insulated. Both commons are used.

Normally both are used, but one can be used if the other is needed for some special purpose.  Some of the manufacturers' track is such that the two outer rails can be isolated from one another, either easily or with moderate difficulty, or with a lot of difficulty.  One supplier specializes (for at least the last 60 years) in track set into grooves in wooden ties, isolating all rails for long distances.

An alternate often found is a special single section where all the rails are isolated, with special insulating pins for the ends of one of the outside rails; more than one of these sections can be used together.

Some of the uses to which isolated outer rails may be put are:

1. With DCS, restricting the power distribution to center and only one outside rail will increase the impedance seen by the DCS control signal, making it effective over a longer block section.  A famous layout to which OGR provided many field trips was wired in this manner.

2. The otherwise unused outer rail on this layout was used to actuate a signal system which showed the presence of another train in the block ahead.

3. The short special track sections can be used to activate accessories such as crossing gates or gatemen.  Special signals with time-delay circuits can be activated by such sections.  These arrangements are specially useful with track systems which may not lend themselves to long sections of fully insulated outer rail track.

4. The two outer rails can be used as a switch closed by the wheel of a train. as above of course, but in this case used where the controlled current is that which enables another train to start up and leave a section on which is has be stopped by reason of the outer rails in its own section having no connection directly to the common (or return) post of the transformer.  In their postwar instruction books, Lionel shows the details of how this is used to automatically run two trains on a layout having a reversing loop at each end of a long single track line; a passing siding was provided at the midpoint where this circuit held one train to wait for the other. Two automatic non-derailing switches were inter-wired in such a way that the second arriving train entered the vacant passing track.  Two others were used in the reversing loops.  The isolated sections were long enough for the engines to coast to a stop.

The idea of course was to eliminate the cost and complexity of relays in those days of limited resources, while avoiding the sometimes tempermental weight-operated mechanical track switches.  I actually built the single line with passing sidings one year; it was quite reliable and fascinating in operation.  The circuit is found quite frequently in various layout books. TMCC signal may be transferred to such isolated outer rails by small capacitors at the insulated pin points.

--Frank   ...Edited to add provision for TMCC, if needed.

Frank, I do understand much of what you said and some is a little over my head. I do need to understand more about what can be done electrically with a layout. Thank's Steve

Stephen - I'm not sure what you're asking but I run a 14 gauge ground to one outer rail and then run a "jumper from that rail to the other outer rail.  A while back forum members recommended this method.  I do run DCS and use isolated blocks on my layout - I have 28 blocks and each block has a hot and ground feeder with the jumper.  

 

Paul

Hi Paul, that's sounds good.I will be putting seven blocks in my layout and I just was not sure if using both outside rails would cause a problem.  Thank you Paul.    Steve