Wiring for Operation

This article first appeared in the November/December 1989 issue of AMRA's 'Journal'.
By Steve Chapman.

For many people wiring is the most complicated part of building a model railway. With most other aspects of model railways it is possible to find a set of step by step instructions on how to do it, this does not seem to be the case with the wiring side of things. The most obvious reason that I can think of for this is the fact that different people, even though they may have developed a layout having the same track plan, will have totally different ideas of how they intend to operate the model railway once it is built, and wiring is to a large extent dependent on the type of operation that is intended.

Wiring of a model railway can be broken down into two parts. The first part of wiring a layout is dependent on the type of turnouts to be used and the track formation. This part of the wiring can be determined using a formula. Live frog turnouts impose the greatest restriction on where rail-breaks and track-feeds must be and either switched or permanently wired dead frog turnouts may be wired to the same formula with the added advantage of being able to replace turnouts when required with ones of another type without having to rewire the layout. The rule to follow here is that all turnouts should have power fed to them from the toe end. To do this carry out the following steps

  1. Put in a rail-break wherever two turnout frogs face toward one another. (figure one)
    essential rail break
  2. Put in a track-feed wherever two turnout toes face toward one another. (figure two)
    essential track feed
  3. If all turnouts face the same way then put a rail-break at the frog end of one of them and a track feed at the toe end of the next. (figure three)
    essential rail break/track feed

This covers the wiring necessary to be able to run a train on a layout using live frog turnouts without getting short circuits and works equally well for other types of turnouts. There are however a number of problems with this amount of wiring.

  1. When two turnouts have their frogs immediately next to one another there is only one place for the rail-break to go but where should it be put when they are further apart? (figure four - question marks indicate some of the places where a rail break could go)
    positions for rail break
  2. You may want to run more than one train (assuming that your track plan allows for it) on a piece of track that has ended up as one big section or hold a locomotive somewhere that would otherwise upset your intended operation. (figure five - question mark indicating optional rail breaks and optional feeds shown dotted)
    optional rail breaks and feeds

This is where the other part of model railway wiring comes in. This part of wiring cannot be reduced to quite such a straightforward formula because the requirements can be completely different even for two people wiring the exact same track plan.

The key to this part of model railway wiring is the intended use to which the piece of track is to be put when OPERATING the layout. No hard and fast rules are therefore possible when you reach this stage in designing the wiring for your layout. Some simple guidelines and examples of how to wire specific track formations in order to achieve particular types of operating potential can hopefully give some idea of how to go about this process remembering of course that it is very easy to bridge a rail break or to add or remove a track feed if you find out that you haven't quite got it right.

 

Let us consider the track formation shown in figure four. There are a number of situations where a formation like this could occur.

One possibility is on a single track line at a station where we have a passing loop so that trains travelling in opposite directions can pass one another. We will assume that the trains will always take the left hand track through the station (swap the wiring for the two tracks over for right hand running). If we have trains approaching the station from both directions at the same time then what wiring do we need to cater for this? In fact all we need is the rail breaks that need to be placed between the two turnouts anyway to be properly positioned so that (with the turnouts correctly set for the approaching trains) that the trains can run straight into the station and be stopped before over-running and perhaps colliding with the other train. The rail breaks in this case need to be set back enough distance from the turnouts to allow a locomotive to run right across the gap and come to a stop before fouling the turnout (see figure six). This distance will usually be the length of the longest locomotive that will be running ON THIS SECTION OF THE LAYOUT plus a couple of inches or so. Once both trains have arrived then the turnouts at both ends can be reversed, the sections at each end swapped to the opposite controllers, and the trains can continue their journey.

wiring platform loops

Another possibility for this type of track formation (perhaps with more than one loop) is when you have a loop off of your mainline. This could be a goods loop, a passenger loop through a platform, or as storage tracks through a fiddle yard. In each of these cases the trains using each of the loops will be travelling in the same direction. Either a train will pull into one loop and another train will pull out of another loop or one train will go straight through past a train waiting in the loop. Again all we need is to have the one set of rail breaks in each loop to achieve the desired operating potential. This time the rail breaks will all be at the one end of the loops (see figure seven) because all of the trains will have their locomotives (and presumably their power pickups) at that end of the trains. As in the previous example the rail breaks should be set back far enough for a locomotive to cross the gap and still be clear of the turnout. With this arrangement it is not necessary to wait for one train to finish pulling into a loop before being able to reset the turnout(s) at the departure end and start a train from another loop on its way.

wiring single direction loops

Loops of one sort or another appear in many places on a railway and one of those places could be a single track terminus. Here we have a loop used for yet another different purpose. If we only have a platform against one side of the loop (as is likely) then the loop itself will only be used to release locomotives so that they can get from one end of the train to the other. In this situation the break on the track nearest the platform should still be towards the end that the locomotive will be at when the train pulls in but since there is no reason why the locomotive can not run right up to the end of the track, there is no reason for setting the rail break back from the turnout and it can be right up against the turnout without affecting operation in any way. There are now two possibilities, either a new locomotive will arrive and be attached to the other end of the train to take it out the other way (in which case there is no problem since the first locomotive is effectively isolated at the end of the line), or the original locomotive will be required to run around its train by using the loop so as to pull the train back out in the other direction. This second case is the reason for the loops existence and we find that the position of the rail break on this track does not affect our ability to operate in the desired way and that the rail break can therefore be placed anywhere on the loop. Figure eight shows the break in the centre of the loop.

wiring terminus platform loop

The situation is of course changed if we have sidings (or whatever else that requires turnouts similarly placed) coming off of our loop. Let us consider the situation from figure eight again but this time place a couple of sidings off of the loop at the departure end (see figure nine). Now we have a crossover between the two lines and the rail break that could have gone anywhere on the loop must now be placed in a fixed position (marked A). This would be the only change required were it not for the fact that we now have another use for the loop line from an operational viewpoint. We now wish to be able to shunt the sidings using the loop line while at the same time allowing a passenger train to arrive in the platform. The arriving passenger train requires that both of the turnouts on the line next to the platform be set for a straight through run. Unless we make a further alteration to the wiring then we will find that this cuts off the power supply to the loop. The solution is to install another rail break (B) and associated feed so as to be able to operate the loop line independently. Note that adding extra breaks, along with the extra feed points that this requires, will not stop any moves that were previously possible from still being able to be made.

wiring terminus with sidings

Wiring for loops which are intended to be two directional is slightly different from the above situations. In figure ten we have two loops between the main through tracks which we intend to use to hold trains which may arrive and leave in either direction. The main lines themselves do of course form loops but they are intended to be used in one direction and are therefore handled in the same way as described above. The central loops (when there are at least two) may be required to cater for an arriving or departing train in either direction. The key to solving this situation is to consider one direction at a time and position rail breaks as required to operate trains first in one direction and then in the other. Once we have done this we find that we have a section of track in the middle of each loop which has been isolated from each end by the rail breaks that we have inserted. Additional feeds to these sections of track are therefore required and should be connected via a switch on the control panel to the same controller that the section of track at the arrival end of the loop is connected to.

wiring dual directional loops

 

Another consideration in wiring your layout for operation is the holding of locomotives. Consider each position where you may require a locomotive to be held. Examine where the feed is that is supplying power to that section of track and the direction that turnouts (if there are any between the position that you are considering and the feed) would have to be set to so as to isolate that piece of track. If setting turnouts in the required direction or switching off that feed would have an impact on any other operational move that you require to be able to make while holding a locomotive at the required position then you will need to install another rail break in an appropriate location between the position that you want to hold the locomotive and the turnout or section of track where the other move is to take place. The section of track thus isolated can then be given its own feed which is connected via an on/off switch on the control panel to the section of which it was previously a part.

isolating section

An example of this is shown in figure eleven. Here we have a terminating track at a station. We intend to operate this track by running a train into the track, uncoupling the locomotive and isolating it at the end of the line, and then coupling another locomotive to the other end of the train so as to take the train back in the other direction. An additional rail break is required at A because without it we would end up with both of the locomotives in the same section of track. The additional feed at B can be powered from C via an on/off switch on the panel so that the locomotive that delivered the train can depart once the turnout feeding the siding has been set appropriately.

 

Although the above descriptions deal with how to wire specific track formations for specific operating requirements almost all of the track formations and operational requirements that you will have can be dealt with by considering them in the way described. Do not just copy the way that a particular track formation is wired even if it matches your formation exactly. Stop and consider your operating requirements, you may need more sections, or may be able to manage with fewer.

When planning the wiring of your layout you might like to consider using the following steps.

  1. Draw in all breaks and feeds required in situations shown in figures one, two, and three.
  2. Where the exact positioning of a break is in doubt consider the operational requirements of the piece of track. Work through each required move one after the other marking in where the break needs to be when making that move. If you end up with more than one position for the break then insert another feed between them.
  3. Consider any long sections of track which are fed via a turnout. Is the restriction of only being able to run on this section of track when the turnout is appropriately set a satisfactory situation. If not then install another break and feed in the desired place.
  4. Consider any really long sections of track. Are they long enough to have two trains both running in that section? Will you ever want to have two trains running in that section? If so install extra breaks and feeds at appropriate distances.
  5. Check the breaks that you have marked in steps two, three, and four. When a locomotive overruns the break will it foul another track which may be in use at the same time? If so them move it back an appropriate distance (check the length of your longest locomotive).
  6. Look at each position where you require a locomotive to be held and insert additional breaks and feeds if appropriate.
  7. Once you have finished designing the wiring for your layout double check it. Consider every combination of moves that you wish to be able to make at the same time. Are there any situations where two moves require to use the same section at the same time? If so then an extra rail break and feed will be required to break it into two sections (of course if the two moves require the same physical piece of track then they can not occur at the same time unless you redesign your track plan).
  8. Reconsider those moves that you discarded as not being required. Would a simple modification to the wiring permit one or more of those moves to be made? Make any straightforward changes because you never know when you might want to make a move that you don't consider to be necessary right now.

And what happens if you find that you want to make a move that your wiring doesn't cater for ? This is bound to happen occasionally and it is usually possible to find a way around it although other trains might have to stop while the move is made (even though their line appears to be clear). If you find that it is happening frequently then reconsider the above steps and install the additional breaks and feeds. Wiring changes are easy to do even on a completed layout.

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Copyright Stephen Chapman