BWWB versus BWBW

by Vic McTee of North Texas T-TRAK Modular Railroad Club

This is still one of the conversations that will not go away with regard to T-TRAK specifications. The following information is provided to inform everyone of the consequences of deviating from the T-TRAK wiring specifications. If your or your club builds the same layout every time, will do so forever more, and will never interact with others - then this information may be nothing more than background information. On the other hand, if you ever desire to have your module "play nicely with others" or you plan on assembling creative layouts then please follow the T-TRAK wiring specifications. It also applies to all scales with the exception of track brand and actual wire colors.

Other than the symmetry of BWWB (more about that later), why do we not use BWBW? As stated on the T-TRAK web site the wiring specification for T-TRAK modules is Blue-White/White-Blue (BWWB). This is also known as "blue to the outside". But what exactly does this mean? Kato uses two conductor wires for track power and one of those wires has blue colored insulation and the other has white. Each of the two tracks on a T-TRAK module has two rails. Starting at the front of the module the first rail will be connected to the blue wire of the power cable for the front track. The second rail will be connected to the white wire of the front track power cable. The third rail belongs to the back track of the module and will be connected to the white wire of the back track power cable. Finally, the fourth rail, which belongs to the back track of the module, will be connected to the blue wire of the back track power cable. Thus, from the frontmost rail to the backmost, the color of the Kato wires will be Blue-White | White-Blue.

The first question typically is asked is why is it wired that way? When T-TRAK was first created the track spacing was 25 mm (center to center). This spacing is the same as butting together the ballast of two pieces of Kato track. The 64 mm feeder track pieces have a small hole to one side where the track power connector goes, however, when the hole was placed between the front and back tracks there was no clearance to insert the power cable, or if connected prior to laying track, the wire interfered with proper track spacing. The solution was to face the holes for the feeder tracks to the outside, thus creating the BWWB wiring scheme. Since this was prior to affordable DCC, it was felt to be a benefit as it permitted two trains to run on different tracks in opposite directions while only using one power supply.

The popularity of T-TRAK grew but many adopted Kato's standard 33 mm track spacing on their modules in order to run more modern equipment. This opened the space between the tracks. Combined with this and other wiring options a switch to BWBW could have been made but there was no compelling reason to change, until Kato released their double crossover. It was quickly incorporated into T-TRAK modules because it was the perfect size for a single module and it permitted trains to switch between the front track to the back track. This was the beginning of the many calls to change the module wiring to BWBW in order to resolve the polarity issue at the crossover. As we know, the current solution is to KEEP the module wiring BWWB per the specification but reverse the polarity for the back track at the power bus or at the power source. This resolves the polarity issue for the layout while retaining the module wiring specifications.

It is important to understand the subtlety in the previous sentence. We deal with specifications for our modules but we have no specifications for a layout. However, to power a layout we need to take the layout into consideration and not the module. The module is merely a standard building block used to construct a layout. When the modules are wired differently it can drastically complicate wiring the layout.

Okay, so why not make BWBW the standard, you may ask. Well, that is an option but before anything is decided we should consider the ramifications of making that change. We know that there is an issue with BWWB wiring but we also have a solution to that problem. Does BWBW have any problems associated with it?

Remember that point about symmetry we put off? It is time to explore it further. Take the following example of two connected T-TRAK singles but instead of both connected in the same manner one has been flipped. This has been done in some layouts and it is usually because the scenery on the backside of the module warrants more attention than the tracks and it makes sense in the context of the layout. Assuming both are wired with power drops the following pictures shows BWWB wiring for both modules.

Singles%20Flipped%20-%20BWWB.jpg

But what about BWBW wiring? The following picture clearly shows the polarity issue we have for both tracks in this scenario. For this example, we would have to reverse the polarity of both tracks, not just one, for this module in this layout context. If the reversed module were one part of a long span of similarly arranged modules, we would have to do this for multiple modules to bring enough power to the rails.

Singles%20Flipped%20-%20BWBW.jpg

It is the symmetry of BWWB wiring that enables us to reverse a module and yet still maintain the correct polarity on the rails. We would need to use the power drop connector for the back track instead of the front track on the reversed modules, but we need not re-wire the module or reverse the polarity anywhere. Because BWBW is not symmetric, much like a standard garden hose, it can only be connected correctly one way. The ramification is that either layout possibilities are restricted with BWBW or wiring a layout becomes increasingly more complex.

Another example to consider is what happens on T-Junctions. Below is a picture of a pair of T-Junctions with BWWB colors for the rails. Note that all three interfaces on the T-Junction have the standard BWWB polarity. So no matter what standard T-TRAK module we may choose to connect, the wiring is what we expect it to be.

T-Junction%20Example%20BWWB.jpg

The next picture is the same T-Junctions wired as BWBW1. At least, that was the attempt. The two interfaces attached via the straight section are as we intended but look at the curved interface. We now have a WBBW interface! If you always build your layout such that the T-Junctions are always paired and your T-Junctions do not have power drops then there will not be an issue. However, if another long span is placed between those two T-Junctions that needs power then it will need to be wired WBBW as well.

T-Junction%20Example%20BWBW.jpg

A final example is this simple version of a mobius layout. This small version is comprised of five corners, two T-Junctions, and a double cross junction. The first picture shows standard BWWB wiring. Following the rail around the layout it is easy to see that it is actually just one circuit. Standard T-TRAK modules with two tracks connected in a layout with only one track! Remember that part about a module is not a layout? Wiring the layout is simply a matter of connecting modules with power drops, both front and back tracks, to the power bus without any polarity reversals. It is just that simple.

Mobius-BWWB.jpg

The last picture shows the same layout wired as BWBW. The polarity problem is shown at the double cross junction but it occurs because of the assymetric nature of BWBW wiring. The only way to resolve the wiring for this layout is to isolate a section of the track and use autoreversing circuitry, or switch to BWWB wiring for the modules.

Mobius-BWBW.jpg

In summary, BWWB wiring, because of its symmetry, is a better all around choice for T-TRAK modules. It does not restrict the types of layouts we can imagine and assemble. It does require care when connecting certain inner loops with the outer main but we have the polarity reversal solution at the power source or bus for that situation. In contrast, with BWBW module wiring each unique layout would require significant study and potential rewiring of modules in order to make the layout work. And our last example proved that with BWBW wiring we could assemble T-TRAK modules into the same configuration as BWWB modules but since we could not easily energize it without it shorting out, we would be left with nothing more than a large diorama instead of a working layout.

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