WiFi control! Digitrax LNWI & WiThrottle

Short summary:

1. Using WiFi for train control is new in the last 11 years, works great and is the way to go.
2. Digitrax LNWI module is inexpensive and provides a dedicated WiFi network for 4 devices (phones, tablets) to control trains and the layout.  It's actually very easy to install and run.
3. You can buy a WiFi throttle device, but easier is an app for your phone or tablet.  
4. Digitrax biggest weak point - the user interface - becomes a non-issue for layout running with a WiFi throttle.  Also makes moot the problems with Digitrax radio throttles.
5. Cons: WiFi interference possible, phones can't be on cell network when being used as throttles.  See main text for solutions.

Switch machine standards

This post describes the procedure and standards I use for installing Tortoise switch machines on the main layout. This is the first of two related posts -- the next post will cover the switch wiring standards.

As I write this I have successfully installed 12 Tortoises on the layout, all driven by Digitrax DS64s. The photos in this post were taken of the last two Tortoises I installed.

This process is not by any means fast. It takes me at least an hour per switch. I don't claim this is the best process, but it works, and it's the product of lots of learning, research, and trial-and-error.

Background: The Tortoise

The normal Tortoise installation position is shown in the picture below, which is copied from the Tortoise instruction sheet:

This photo is a bit hard to decipher because it is in black-and-white, but the components are all there. At the top you can see the switch (they use HO scale in this picture, but the same machine works for N and other scales too). The switch is on top of roadbed, which looks white in this picture, and that in turn is on top of a piece of plywood subroadbed. There is also a shaft drilled through the cork roadbed and plywood subroadbed. The Tortoise is attached underneath the plywood. A non-electrical metal wire, which I will call a "driving wire", links the Tortoise to the switch through the shaft. The driving wire goes through a “fulcrum”, or pivot point, which is piece of plastic with a small hole for the wire near the top of the Tortoise in this picture, then down to a screw near the bottom that holds the wire to the gears. When the gear shifts from one side to the other, the wire is moved and the switch above will move to the opposite side.

This is a simple but cool mechanism. Because of different scales and different thicknesses of subroadbed, the span of the “throw” at the top of the driving wire (that is, the distance the wire covers at the top when going from one side to the other) can be adjusted by moving the fulcrum up and down. The instructions also say that you can substitute a larger gauge wire if you like, and this can be useful in some situations.

Extending out of the bottom of the Tortoise in this picture is a circuit board for 8 electrical connections. The Tortoise is driven by a low DC voltage using the 1st and 8th connections. To “throw” the switch you simply reverse the polarity of the DC voltage being supplied, and that causes the gear to switch sides. Once the gear has gone all the way to one side the motor stalls. It can still receive power without causing problems, and depending on your situation you might want to keep the power constant to be sure the point rails are held against the side rails.

The other 6 connections on the circuit board are linked to two internal SPDT switches, which are switched whenever the main switch is thrown. The most common uses for these are to provide switched track power to the frog rails and to wire lighted indicators for a switch board. I will be using both of these functions, but this post only describes the frog wiring as I haven’t set up the light boards yet.

A sideways installation: concept

I chose not to install my Tortoises as described above, for two reasons. First, you’ll notice the Tortoise sticks out quite a ways under the layout – almost 4” when you consider the wiring attached to the circuit board. I simply won’t have that much available space under the upper deck, nor at certain parts of the lower deck (such as above the power cabinet). Furthermore, even where there is 4" of vertical space I prefer not to have the Tortoise taking up that much head room in the under-layout crawl area.

Second, on the lower deck of my layout there are many places where the thickness of the foam subroadbed plus the underlying plywood is as much as 2 ¾”. This means the driving wire has to be extra long, which is not by itself a problem. But it also means that the span of the “throw” of the end of the driving wire is huge, even if the fulcrum is moved to the absolute top of the Tortoise. Add in the fact that I’m in N scale, and what this means is that with a normal Tortoise installation the “throw” for the wire is 3x the distance needed to move the turnout (switch) from one side to the other. In practice this is still workable, as the wire is bendable. But the downside is the aesthetics. One of the key benefits of the Tortoise is that your switches move in slow motion, like the prototype. At a typical DC voltage the time it takes to move a switch from one side to the other is about 3 seconds. However, when the “throw” span is 3x the width needed to move the switch, what happens is that the switch is moved in 1/3rd the time, or about 1 second, and that means the appearance is way too fast.

Both of these are common problems and thus there are many proven solutions. The Circuitron people even sell special sideways Tortoise mounting kit to address the first problem (but not the second). A while ago I ran across a link to this model railroading news letter where on page 8 the author describes his procedure for sideways mounting. As I studied it I realized that not only was this cheaper than the official sideways mounting kit, it also had the added benefit of addressing the second problem (although that was not the author’s intent) because of the geometry of the two wires and fulcrums.

The procedure I use is copied from his, making adaptations only because I used different materials that were more readily available. After successfully testing this with one switch, I modified the remaining 13 Tortoises that I had on hand as shown in this picture:

My goal in the modification of the Tortoise is to prepare it for an installation that looks something like this, viewed from underneath the layout:


Note that both Tortoises in this picture are mounted sideways. The wire that drives the switch still runs through a vertical shaft in the plywood, but now there are two wires and two fulcrums.
The rest of this post describes how to set up this installation.

Preparing the Tortoise

1) You are going to glue two pieces of styrene to each Tortoise. In preparation, you will file down Tortoise plastic “shell” slightly just to make sure there is a smooth surface to glue to. I first used a hobby file, but then went to a normal sized metal file as it was quicker. The first place you need to file is what will be the “top” of the Tortoise when it is installed – this is the side opposite the side with the gear. You probably have to take off the round sticker that the inspector put on it and then need to file down the “bump” down the middle where the two plastic pieces of shell were joined. Do so for the whole side. The second place you need to file is the side that is the “top” in a normal installation. Again, file down the bump in the middle.

2) For what will be the “top” of the Tortoise you will want to attach a piece of .030” styrene about 2 7/8” x 2 3/4”. This styrene will act as a mounting plate. As per the picture above, you see there is a plate of white styrene attached to the top of the Tortoise with glue, and the plate is screwed to the plywood to mount the Tortoise. I bought some large sheets of .030” styrene in bulk and cut them with a plastic cutter. Thicker styrene can also work – I would not recommend thinner. Once cut, I attach the styrene using common super glue, which dries very fast and holds strong.

3) You’ll need a second, smaller piece of styrene to act as the second fulcrum. In the picture above this is the piece of white styrene at the very left of the photo, attached to the Tortoise very near the plywood, and with the driving wire running through it. For this I used .040” styrene, cut to 1.5” x 1/2"”, and used super glue again to attach it to the Tortoise. It’s a good idea to drill the hole before attaching. I placed the hole in the center, lengthwise, and about 1/8" from the end (widthwise). The hole should be big enough for the wire, and after the hole is made you probably want to tilt the drill at an angle and move it in a circle to provide an angled cut so that the wire can tilt as the switch is thrown.

4) For driving wire some people recommend .025 piano wire. I use 18 gauge wire that I found at the local Michael's art supply store in the floral section. It's intended to serve as a stem for fake flowers, but it's very cheap, is available in bulk packages, is perfectly straight until you bend it, and can be cut easily. It's thicker and stiffer than the wire which comes with the Tortoise, which is an advantage, so I use it for both of the wires in each installation and save the stock wire for some unknown future use. The wire lengths should be cut to fit your installation, with some extra left over just in case.

If you use the thicker wire you'll need to drill larger holes in the Tortoise fulcrum and in the slot where the wire slides into the gear. I recommend buying a small hobbyist hand drill with an assortment of small bits -- you can use this for all kinds of model projects, and the hand drill is easier to control than a power drill. I choose a bit that is exactly the size needed for the 18 gauge wire.

For the gear slot, I use hobby pliers to hold the black plastic gear while drilling -- this prevents possibly damage by pressing too hard onto it. Ditto for when the screw is added. When that wire is in place add the green fulcrum, putting the wire through it.

5) Then you join the driving wires, one each for the styrene fulcrum you added and the green fulcrum that came with the Tortoise. There are many options here, but the easiest I found is to use a short (1/2" or so) length of chunk of retangular, tube styrene available at any decent model train shop (Evergreen Scale Models #259, .250 x .375"). I drill cross holes in each direction and put the wires through. While there may seem to be a lot of slack in this set up, in practice the first wire moves the second like clockwork.

6) For final touches, first add 4 holes to the edges of the mounting piece of styrene and pre-set 4 screws (I use #6, 5/8"). Then I add a label for the switch number. This shows a Tortoise where everything is ready for installation. Note it is upside down and the second driving wire isn't in the picture -- that will get added during installation:


Preparing the Switch

There are three things you need to do to prepare the switch for Tortoise installation (or possibly 1 or 2, depending on your type of track). It is easier if you do these before you install the switch on the layout, but alas I'd already installed these switches, so I had to do these things after the fact.

First, here is an example of two Peco code 55 switches, installed in 2006 and still on the original AMI roadbed:


So here's the modifications that I make:

1) First, I connect a feeder wire to the frog rails. I described this issue with "Electrofrog" or "Live Frog" switches last year. In my case, I had hoped that I could avoid having to make the extra effort to add a separate feeder wire the frog rails, but my experience operating the layout proved that in the absense of a separate feeder wire, the frogs frequently lose power due to dirt between the point and outside rails. You can correct this immediately by cleaning the rail contact points, but on a large layout you have to do this a lot during operating sessions, so it quickly becomes tedious.

Adding a frog wire retroactively to an installed Peco code 55 switch is a challenge, but doable. There is a connecting frog wire hidden underneath the switch. I found that I could access it from the outside rail of the straight route, between the 2nd and 3rd tie from the end. I used an eXacto knife to first cut out some roadbed, then cut the plastic under the rail, and then "dug" a bit into the under-rail plastic until I caught the wire on the end of the knife. I would then pull the wire out just enough for it to be visible. At that point I would strip about 1/2" of insulation off of a 22 gauge solid green wire, bend the end of the wire into a hook, and use it to "hook" the exposed frog wire. Once hooked I'd use small hobby pliers to clamp the wires together, then solder them, then drill a hole in the plywood for the green wire. The end result is a hidden feeder wire connecting to the frog rails on one end and sticking underneath the layout on the other end.

2) Peco switches have built in springs that force the switch to one side or the other. This is a nice feature in the absence of a separate switch machine. However, when using a slow-motion Tortoise the spring needs to be removed.

The spring is located right at the end of the point rails. You will see two metal tabs on the plastic part between the rails that spans two ties. Use and eXacto knife or similar to pry these up, then remove the plastic tab in the middle. Then push the metal tabs down so that you can remove the piece of metal that includes thow tabs. Finally, the spring itself is now visable. Pull it out with hobby pliers or a tweezer. You're done.

3) Finally, you need a hole for the driving wire that will link the switch to the Tortoise. I use the hand drill mentioned earlier. This hole should be in the large tie that drives the movement of the point rails, and I prefer putting the hole in the exact center of the tie between the rails, rather than, say, on the part of the tie on side of the rails. It just seems to work better that way.

First, I use a small drill bit to create a pilot hole, then a larger drill bit that is the exact size of the driving wire. Be very careful, as too much downward pressure can damage the switch.

4) One other thing you'll need is to drill the shaft through the subroadbed for the switch machine wire. I use a 3/8" bit, and am sure to clean the shaft of debris before installing the switch.

Here is a switch which has had all of the above steps completed, and even has a driving wire in the wire hole. At this point the switch machine below is not connected, so the wire has been slightly bent at the top to prevent it from falling through:


Installing the Tortoise

With the switch and Tortoise both prepared we are ready to connect everything up. Depending on the space available underneath this can require some real physical contortion to reach everything. To the degree possible try to provide adequate space and light. I use at least two cheap "clamp" worklights available at hardware stores. It's good to have two to provide lighting from different directions so that you avoid shadows.

1) Prepare the space.

Make sure there is a spot under the layout clear of wires and other obstacles. Here is an example of such a space:


On the left side of the picture you can see the bottom of the shaft for the driving wire, and the wire itself hanging down from the switch. Next to that hole is a white shelf support bar -- because of that we won't be able to install the Tortoise to the left of this shaft, we'll need to do it to the right of the shaft. On the right side of the picture you see the green feeder wire from the frog. In the middle of the picture is the red-and-black power bus. This is near the intended location of the Tortoise, but not in the way.

The Tortoise itself has to be positioned so that the movement of the switch wire is perpendicular to the switch itself.

2) Connect the Tortoise to the plywood.

Here's a picture showing this step completed:


This is a pretty simple step conceptually. Position the Tortoise such that the driving wire is through the styrene fulcrum (see left of picture) and that the fulcrum hole is at the center of the shaft. This gives the wire maximum movement potential -- if the hole is too near the sides of the shaft the you may find the switch doesn't move well. Also make sure the Tortoise is lengthwise positioned in the same direction of the switch itself -- this is to make sure that the wire movement is perpendicular to the switch. Then drill the 4 screws in and you are done.

In practice this is tricky. I usually put in the first two screws manually, at least part of the way, to make sure they go in straight and don't shift the location of the Tortoise. Then I use a power drill on slow speed setting with an extra long drill bit to keep the screws going in straight.

3) Connect the frog wire.

Here is a Tortoise with just the one frog wire attached, not yet soldered:


There are two options for adding wires to the Tortoise circuit board. One is to buy a 3rd party "slide on edge connector" which have wire clips on one side and a slot for the whole unit to slide on the tortoise circuit board on the other side. This is the smart way to do it, as it saves difficult soldering and allows for easy changes later.

So, since that is the smart way, naturally I do it the other way. Mostly out of trying to save money where I can. I solder the connections. Now, this is quite tricky but I've gotten so I do it quickly and reliably. And I figure that if I need to make changes later I can do so at the other, non-soldered, end of the wire.

After I have the Tortoise in place I think of the circuit board as having slots numbered 1-8 from left to right, from the point of view where you are sitting looking at the board directly (as in the above photo). In this case slots 1 and 8 will be used for the switch power from the DS64. I connect those wires last because it is easier to solder the inside slots first. Slots 5-7 will be used in the future for the switch board lights, so I don't talk about them in this post. Slots 2-4 are for powering the frog.

Slot 4 is the frog wire. This is the unswitched side of the connection, as shown in the internal Tortoise SPDT diagram below (taken from the Tortoise instructions):


I'll have more to say about the above diagram on the next step. For now, the point is that slot 4 is always for the green frog feeder wire.

Attaching and soldering is the same process for each wire. First, I strip about 3/8" of insulation from the end of the wire. The wire is then routed through the hole and, using hobby pliers, the wire is bent as shown in the picture above so that it forms a "U" shape and clamps onto the circuit board. You want to have only a small amount of wire extending above the board, and you want to make sure that there is no chance that any two wires above the board will touch each other. Below the board there is a thin, narrow strip metal for connectivity, so you want to run the wire along that metal strip.

Once in place, I use a soldering iron at 40W (the 20W setting doesn't work as well for this application). I place the flat end of the iron blade on one side of the wire and make sure it is touching the circuit board metal strip, then apply solder from the other side of the wire. The whole process takes only a few seconds -- as soon as the solder is applied I remove the solder source and the iron. The solder will tend to bind to the metal, not the insulation between the metal strips, if you are spartan with the solder there should be no shorts yet the connection should be solid.

4) Connect the track power wires

This picture shows the same Tortoise after the track power wires have been connected:


It's not clear from the picture, but the red track wire has gone to slot 2, the black to slot 3. The track wires are connected to one of the terminals on the power bus, as described in earlier posts on wiring standards.

The biggest challenge at this point is figuring out which track polarity goes to which of the two slots #2 and #3. There is no simple rule of thumb. It depends on the orientation of the switch itself and the orientation of the Tortoise. The only solution I found that works is a complicated procedure. I first look at the switch from above and mentally identify which rail is "red" and which is "black". Then I note whether we want the frog rails to be "black" or "red" when the switch is set to the "normal" or "straight" route. In that case the frog rails should be the same polarity as the outside rail from the diverging route.

Then I mentally note whether, in the "normal" position, the switch is set toward the wall or away from the wall. Thus, at that point I might be thinking "switch set toward wall, polarity black", for example.

Then I climb under the layout and position myself so I am looking at the Tortoise from the side of the circuit board. Let's say, from that point of view, that the "toward wall" position matches the left side of the Tortoise. So I will now say, "switch on left side, polarity black".

Now I look at the internal Tortoise SPDT diagram shown above in the previous step. At the bottom of that I have manually drawn in two boxes and a line connecting them. This represents the two possible positions of the switch. The box on the left is filled in, the box on the right is hollow. So what this says to me is that when the switch is on the left, the internal SPDT switches will be in the position shown in that diagram. When the switch is on the right, the internal SPDT switches will be in the opposite position.

And from this, I know that if "left side, polarity black", then if the switch is to the left slide, then slot 4 (frog) will connect to slot 3, so slot 3 should be the black wire.

Then after doing all that I repeat the mental exercise to confirm the result, then I attach and solder the wires.

After doing this for 11 Tortoises I've found it works every time. The only time I made an error in polarity was when I tried to short cut the process with a "rule of thumb", copying the wiring on a nearby Tortoise, but missing a detail so I made an error.

5) Connect the switch power wires

This picture shows the same Tortoise after the power wires were connected to slots 1 and 8:


One thing that might be confusing is that there are two pairs of white power wires -- one coming from above, and another extending below. The reason is that the Tortoise in this picture is one of a pair of Tortoises that drive a crossover. Crossover switches have the unique attribute that they should always switch together. That is, it makes sense only if both switches are set to "diverge" (so that a train can crossover between the dual tracks) or "straight" (so that trains can pass each other on the two tracks). So, in this case we wire the power for both Tortoises from the same DS64 switch slot, saving a switch slot and simplifying the control.

Therefore, the second set of white power wires are hanging down in this photo only temporarily. They will soon be connected to slots 1 and 8 on the paired Tortoise.

6) Connect the Tortoise driving wires

This photo is a repeat of the photo at the beginning of the post, and shows the paired Tortoises all set up:


You'll see that the driving wires are now connected using the piece of rectangular styrene tube. Back during the Tortoise preparation phase I drilled holes in the piece of tube so that perpendicular driving wires could go through both ends. Now the driving wires are routed through the holes.

It's worth remembering that the driving wire which goes to the switch will not be supported from above after this installation is complete. Therefore, in order to prevent it from sliding down and falling out, we need to support it from below, This is done by bending the bottom part of the wire around and using pliers to clamp it onto the rectangular styrene "connector".

7) Testing and tuning

Everything is in place but there is still quite a bit of testing left to do.

The first tests I run by powering up the DCC command station but not adding track power. The first test is simply to see if the DS64 actually drives the Tortoise using the switch address we thought we programed. Note that you may not see the switch actually move at this point (although it's better if you do), however, if you see the Tortoise switch gear move in response to the command then the test passes. If you have paired Tortoises, both must move, and their movement must be coordinated (so that both switches are either diverge or straight at all times). If this fails you need to check that the address is correct and then that the wiring is correct. (Or, if this is the first usage of that DS64, you need to verify that it is getting power and Loconet correctly.)

The second test is to make sure that the DS64 "thrown" and "closed" positions match that of the switch. If not the simple solution is to reverse the two wires that connect to the DS64. In fact, although it is possible to reason out in advance which switch power wire should go to which DS64 slot, in this case it's not worth the bother. I just connect the wires to the two DS64 slots randomly and half the time I end up having to undo and reverse them them -- a process that takes less than a minute. (Note: the reason I don't use the same process for the frog wires is that with frog wires we are dealing with soldered connections and the power test takes longer run.)

The third test is tuning the switch. Ideally as soon as the Tortoise gears starts moving the point rails will start to move from one closure rail to the other -- and get to the other closure rail just as the Tortoise completes the movement. You don't want the point rail to not reach the closure rail, obviously, but you also don't want it to get to the closure rail too soon either, mostly for aesthetics as noted earlier.

One adjustment is to move the green fulcrum on the Tortoise to increase or degress the span of the driving wire movement. The other adjustment is to slightly bend the wire if the switch is favoring one side or the other. This adjustment takes practice, and the first time you try it you may decide you need to start afresh with a new wire after too much bending. However, once you get familiar with the process this adjustment is usually completed and tested very quickly.

Once the switch itself has been tested for correct connections and movement you can remove the top of the driving wire that was sticking out the the switch hole. Thus the switch will end up looking like this:


Note that you can barely see the end of the metal wire in the middle of the switch tie. After adding scenic treatment this wire will be completely hidden.

The final test is the power to the frog. For this you turn the track power on. There are two tests. The first is to see if the polarity is correct. If not you'll probably know as soon as you turn the track on because the frog will short, as the point will be touching the wrong rail. However, just in case the short is masked by some dirt between the point and closure rails, also test with a voltmeter on an A/C setting.

The second test is to make sure the frog is getting power separately from the point-closure rail connection. That is, test to verify that the frog feeder and red/black track power wires you connected to the Tortoise are actually routing power. Using the voltmeter on the A/C setting, first test to see what normal track voltage is between two nearby rails. (For my layout, it's usually 12.6V or so, which is correct for Digitrax on the N scale setting.) Then put one lead on the frog, one lead on a nearby rail of opposite polarity, and manually move the switch so that neither point is touching a closure rail. The voltage should stay the same -- if not the frog feeder connection is either tenuous or non-existent. Throw the switch and repeat again, to verify this works with both polarities.

Now you are done. This post didn't cover the wiring standards or the programming standards for the DS64. I'll cover that in my next standards post.

Wiring Standards part 6: Power cabinet and Loconet

I created a number of posts last year about the wiring standards for the layout. This post extends on those by describing standards that have been developed and/or refined as a result of the power cabinet work last weekend.

Here is how the cabinet looks most of the time:


The goal was to have a clean appearance with everything easily accessible for operations and maintenance. Regular operations can be performed by opening the cabinet to start the layout and get the throttles -- at which point the doors can be closed again until operations are over. For maintenance the cabinet can be pulled away from the layout, since it is on rollers, to access the wiring in back of the cabinet or underneath the layout.

Here is the view with the doors open (in this view the cabinet is pulled away from the layout):



The top shelf is currently for storage of throttles and of Digitrax manuals. I've earmarked key pages that get frequent use, like CV tables, how to program consists, Ops mode programming steps, etc. As the number of throttles grows I'll likely need to have a separate place to store them.

The second shelf has the DCS100 command station on the left and the power strip on the right. The power strip is screwed lightly into place and all the power supplies needed for the layout are plugged in place. If you click on the photo for the larger view you'll see they are also all labeled with their purpose. In this setup, under normal operations the starting and stopping of the layout is done with just the main switch on this power strip.

The DSC100 has various wires attached to it but I've tried to keep those organized too. The power and ground outputs, red, black, and green, go directly from the DCS100 to the barrier strip on the left wall. Any device that needs connection to the DCS100 is connected to the barrier strip, not to the DSC100 directly. All power wire is 14 gauge, and as with the rest of the layout pairs are twisted together and labeled.

The DCS100 also has a programming track set up in front of it. This allows for quick decoder programming during an operating session if for some reason Ops programming won't work. It can also be used at other times, but for normal locomotive work I'll probably use the Digitrax Zephyr at my work desk.

The empty space on the second shelf is reserved for a booster, which may be needed when I start building the upper deck of the layout, or for a second power strip.

The third shelf is for power management, as can be seen from the labels in the larger picture. On the left is the PSX4, which provides power to districts 1, 2, 3 and the auto reverse (AR) sections that are controlled by the PM42 (the middle device). These are lightly held in place and have padding protecting them from the shelf itself. The empty space on the right is reserved for the second PSX4 for the upper deck districts. As I plan to have 8 power districts plus a district for the PM42 I will also need a PSX1. I plan to place that in front of the PM42 and wire it to the PM42.

During operations if we get a circuit break or if we otherwise have to view the power management LEDs for problem diagnosis we simply open the cabinet to see them.

The bottom shelf is currently occupied only by the main power supply for the DCS100. (It's a DCC Specialties device, recommended by Mike Gleaton.) The rest of the space is reserved for an additional power supply for a booster, if it turns out that is needed, and for transformers for the lights and switches.

Here is a look behind the cabinet:


This does look a bit messy with all that wire, however if you look closely you'll see I've tried to tame the mess a bit by setting up hooks around the back of the cabinet for routing the wires. Plus, the wires are all organized into labeled, twisted pairs. However, because the cabinet must be allowed to roll away from under the layout there has to be some slack in the wires that connect the cabinet to the layout. All these wires can be disconnected, if need be, by plug or by undoing the electrical pigtails, and all are labeled to allow easy reconnection. However, the slack wires do make it look messy. The wires for power districts 3 and 4 and for the upper deck AR section have already been deployed, so that attaching these later will be a simple matter of connecting them to the wire ends at the back of the cabinet, instead of having to add wires inside the cabinet.

One other minor wiring standard emerged from this work, and that had to do with the Digitrax UP5, UR91 and UR92 front panels. These are distributed throughout the layout on front fascias to allow plugging in of Digitrax throttles anywhere. UR92 is the two way radio receiver panel, the two UR91s are one-way radio receiver panels, and the UP5s are basic panels.

These panels have two wired connections. One is Loconet, a 6-pin cable. The other is a single 18 gauge power wire. The single wire, together with the loconet ground wire, allows up to 10 panels to share a single power supply. The UR92 doesn't have the power wire because it requires a dedicated power supply. The power supply for the 10 other panels is connected to the UP5 nearest the power cabinet.

One standard I'm following is to configure the loconet in a branching configuration, avoiding loops, per the Digitrax recommendation. The other is to label the power wire "UP5" every few feet to distinguish it from other wires. The Loconet cable is not labeled, as it is clearly unique.

The last point is placement of the panels. Usage-wise, radio throttles can connect to any panel, not just the radio ones. The one-way throttles use any panel to plug-in to select or dispatch locomotives, but once that is done the throttle is disconnected and communication is automatically done via a one-way receiver. For this reason the two UR91s panel/receivers are placed in the two different rooms, and roughly in the middle of the rooms. The two-way throttles don't need to plug in at all unless they get confused, however they do need to be initialized when they start up by plugging into the UR92 for two seconds. For this reason the UR92 is placed on the right side of the cabinet, so that you can plug in at the same place that the throttle is stored. That also is roughly the center of the layout, which should minimize any chance of radio interference. You can see the UR92 panel in the upper right of the first photo with this post.

Atlas Code 80 Switch Prep Procedures

Atlas Code 80 track and switches have seemingly been around forever, literally since the 1970s or 1960s. They are still sold today because they have one huge advantage: price. An Atlas Code 80 #6 remote switch, which includes a snap relay switch machine and a switch control box, can be bought for $13.35 at Brooklyn Locomotive Works. By comparison, the combined cost of the more widely preferred Atlas code 55 #7 switch with Tortoise switch machine and a typical SPST switch box will run you at least $25 -- and other options such as Peco or MicroEngineering switches are significantly more expensive even than that.

Of course there are reasons Atlas code 80 is so cheap. First, it doesn't look anything like prototype track. Second, functionally speaking the slow-motion switch machines are superior to the old snap-relay variety. And third, there are valid concerns with the Atlas code 80 switches' out-of-the-box reliability.

I use Atlas code 80 in staging because: 1) prototype-like looks aren't important in staging, and 2) with 73 switches combined in my 5 staging areas the cost savings are significant. This means I had to come up with a solution to address the Atlas code 80 switch reliability problems, and that's the topic of this post.

Here is a picture of an Atlas code 80 #6 switch in package next to one that has been prepped for the layout. I've added three circles at places on the prepped switch to help with the explanation of the prep procedures. To get a bigger view simply click on the picture:


As far as I know the procedures here will also work for Atlas' smaller #4 switches. However, I recommend #6's because they are longer, with a wider curve radius, and thus more likely to operate reliability with any N scale equipment.

One point worth noting is that Atlas has improved these switches many times over the decades. Most of the chronic problems that were documented in the 1980s, for example, have been addressed in the current version. The issues that remain are addressed in the steps below:

1. Open the package. The switch controller and screws can be set aside until if/when you are ready to use them for switch control. The 6 rail joiners should be separated with a cutter, such as the Xuron rail cutter, and trimmed so that there is no excess metal on the ends of each joiner. I then put them in a rail joiner drawer until they are needed on the layout.


2. Inspect the switch. Look for track out of alignment and test the switch machine manually. Use a truck, such as a Micro-Trains replacement truck, to see if it catches anywhere when run over the switch. Once you've followed these procedures with several switches you'll probably be able to see the problems areas by eye without testing.


3. Look closely at the rails inside the red circle in the photo above. This is where the closing rails meet the point rails. I find it helpful to use a magnifying visor for this step. In almost all cases the closing rail is not in line with the point rail (the point rail is the one which moves), but instead sticks out a little. This "sticking out" can cause trucks to skip over the bump and in bad cases can lead to derailments. Using a small metal file gently file down the side and top of the closing rail end, and if necessary the end of the point rail as well, until the transition from one rail to the next is smooth. Note that this problem usually affects the diverging route but not the straight one, but just to be safe I file the rails for both routes.


4. Now inspect the plastic frog inside the yellow circle in the photo above. In some cases the frog is too big and thus can cause wheels to bump up when they travel along the frog. The solution is to file down the top of the frog tip, then file the sides of the frog tip to assure that wheels pass by smoothly all the time.


5. Check the ends of the point rails (shown inside the green circle in the photo). To be honest I've not seen a problem with these in the current generation of Atlas code 80 switches, but historically the point ends can be off level with the main rails. If so you'll need to add shims under the point rails or file down the rail tops as appropriate.


6. Now test the switch machine. This can be done by wiring it up per the instructions on the back of the switch package. However, to save time you can take two wires, one black and one of another color, and briefly touch them to the accessory terminals on your DC power pack. Then do the same with the other color wire and the black wire. Test only once, to avoid overheating the switch machine. Again, I've not experienced any out-of-the-box problems with this generation of Atlas code 80 switch machines, but if a problem does arise I want to find it before I install the switch on the layout


7. Finally, as the switch wires are short you'll probably need to extend them. I strip about 3/8" of insulation off each wire and crimp yellow butt splices (gauge 16-22, as shown in photo) that are found at Radio Shack. I don't add wire to the other side of the butt splice until the switch is on the layout, as until that time you won't know how much additional wire will be needed.

After that the switch is ready for the layout.

Wiring standards part 2: Amendment

One minor addition to the Wiring standards part 2: Terminals and Feeders post: The terminals will always have the black wire connections on left side, red on right side.

Why? Just because.

Wiring Standards Part 5: Staging Switch Wiring

Staging uses Atlas code 80 switch machines, which have 3 output wires (red, green, black) of a very small gauge (28? possibly smaller?). The very small gauge is fine given that the machine is designed to accept only a short burst of current when the switch is thrown, and otherwise have no current running.

The wires that come attached to the switch machine are about 12" in length, so require extensions since the distance from switch-to-control panel is at least 3' and usually longer. For the wire extension I am using a "Rainbow" cable from Radio Shack, which is a ribbon of 4 solid 24 gauge wires in colors white, red, black and green. Connections from the ribbon to the switch machine wires are via clear 22-26 gauge butt connectors, also from Radio Shack, with the white wire left in place unused. The butt connectors are reasonably cheap ($2 for a pack of 24, which covers 8 switches) but the rainbow wire is $8 for a 20' roll, so I've got my eye out for alternatives.

Wires are labeled as other wires, with a labeling scheme of number-location, such as "4M" = 4th switch on the Middle tier. Numbering is generally sequential but that is not guaranteed. The wire number is currently the same as the switch number that will be used in operations schematics, but I reserve the possibility of changing the switch number for operations improvements without changing the wire number. Current locations are L (Lower tier), M, and U (Upper tier). The number-alpha format is designed so that switch machine wire labels don't get confused with the alpha-number format of track wires. However such confusion is unlikely anyway given that rainbow strips of wire are visibly very different than the red-and-black twisted pairs for track wire.

Switch wires are run under the subroadbed and bundled together with plastic cable ties to keep them tidy and reduce the possibility of pulling a switch wire out by mistake while reaching for something else.

Switch wires are run to the temporary control panel made up of Atlas switch controls. When the permanent switch control solution is designed some of this wiring may need revision, but at this point I think all that will be required is to disconnect the wires from the Atlas switch controls and connect them to the permanent device.

Wiring standards part 4: Auto Reverse and gapping

I was going to start this post with a description of Auto Reverse (AR) sections -- what they are and how they work. Then it occurred to me that someone else probably already had done that and, sure enough, you can find such a description at Wiring for DCC.

My layout will have 6 standard AR sections, 5 for the return track in each of the staging areas, and one for the wye at Union Station. There will also be one crossing with live frogs on the upper deck, and that requires a special application of an AR device. I'll address that topic in a later post, probably not until upper deck construction is underway.

Before getting to the wiring standards, there are a couple of AR section design standards to mention. First, all of the 6 standard AR sections will consist only of a single track, no switches or crossings. This not only simplifies installation, it also greatly reduces the possibility of accidentally triggering the AR device through electrical shorts (more on that later in this post). Second, standard AR sections will be at least one train length long -- some possibly fitting two or even three shorter trains in a pinch. In general you want AR sections to be at least as long as your longest train. This is pretty obvious if you think of every car as potentially carrying electrical current in the wheels. It's true most freight cars have plastic wheels, but many have metal wheels, and all it takes is one wheel to bridge an insulating gap and cause a short.

The AR wiring standards will be:

1. Each standard AR section gets its own power bus. Terminals won't be needed, instead feeders will be connected directly to the bus.


2. AR devices will reside in the power cabinet, making them easy to track with the other power devices and easy to debug problems.


3. The AR bus wires will be colored blue and yellow to distinguish them from the other layout wires. It doesn't matter which rail gets which color, so by convention I make the rail that is closest to the nearest wall for most of the AR section yellow. No reason, just because.


4. The wire for each AR bus is 16 gauge stranded. 14 gauge would be overkill because a) the length of the AR buses top out at 20' and b) the amperage draw will be much smaller than for the power district buses. 16 gauge stranded wire is available reasonably cheaply at Home Depot in multiple colors. The blue/yellow bus wires will be twisted to keep them together. They are labeled with "AR" and the name of each section, such as "AR-Upper Tier".


5. AR feeder wires are 22 gauge like the other feeder wires, are black, and like the other feeders are soldered to every other rail joint. Each feeder is directly connected to the appropriate AR bus wire. This is done by stripping a 1/2" off the bus wire insulation and the end of the feeder wire insulation, wrapping the exposed feeder wire around the bus wire, soldering, covering with electrical tape and then scotch tape, as electrical tape doesn't stick well. The electrical tape isn't really needed except that it might prevent oddball shorts in strange situations.

The photo below shows part of an AR section with the associated wiring:



The track nearest the camera is the return track for the lower tier. Below the track you can see the twisted blue/yellow AR bus wires, and at the left you can see an attached label with the name "AR - Lower Tier". On the right you can see two black feeder wires connecting the rails to the bus. You'll note that there is electrical tape around the connections, and scotch tape on top of that.

Part of the AR wiring standards remain undecided. First, I'm not sure what AR device I'll use. I have one Digitrax AR-1 on the layout now, which provides a simple AR function for one AR section, and it works like a champ. There are a few complaints about this on the internet forums, but mine has worked perfectly out of the box without need for adjustment. It may be that most of those who have trouble are using larger scales, or older locomotives. N scale may help in that I'm using lower voltage (the Digitrax DCS100 command station has an N scale setting) than HO, or that N scale locomotives draw less current.

On the other hand, I might have just been lucky with my one AR-1. But, I am currently leaning toward sticking with the AR-1 until/unless troubles arise. However, I hear good things about DCC Specialties' PSX, which replaced the similar Tony's Trains products, so they may be worth the small extra outlay in costs.

One product I recommend *not* using for auto reversing is Digitrax' PM42. I bought this because it was advertised as a low cost way to have 4 AR sections. That is technically true -- if you have a separate 12-18V AC power supply lying around doing nothing. And if you have a DT300 or DT400 command throttle to program it. And on top of that you'll need to do a nest of soldered wiring for the inputs and outputs. But the final kicker was that after I'd spent a couple of hours soldering everything and getting it all in place I found out that one of the 4 sections was faulty. ARGH. Yes, Digitrax support is excellent and they would quickly replace it, but that would have meant unsoldering everything, filing a support ticket, printing it out, and going to the post office to mail it. I've decided to accept the bad section and let the other 3 get used for power management.

The other pending decision is whether to connect the AR sections directly to the power booster or route it though a power district, and if so which one (maybe put all ARs in one power district). Logically you'd probably want ARs under a power district so that they don't short the whole layout. Except that there are frequent discussions on the forums about conflicts between an AR device and a PM circuit breaker. Fortunately, as all these devices will be in the same cabinet I can defer the decision, and once made it can be changed easily.

Finally, AR sections, like power districts and "live" switch frogs, require insulated gaps. You can either cut a gap in a rail and optionally fill it in or you can use an insulated rail joiner. I prefer the latter, and as a standard use the Peco insulated joiner even for Atlas track. It's smaller, hence less obtrusive, but it does a much better job of holding the rail in place. It can be disguised well as part of track scenicing. A situation may come up where the rail joiner is not practical, such as where the joint is on a tight curve, but until then insulated joiners are the standard.

Wiring standards part 3: feeder wires and track

In the last wiring post I covered the power bus terminals and feeders leading from the terminals. Now I'll cover the standards for connecting feeders to the track.

The first question is: how many feeder wires do you need per length of track? When you buy a starter train set with an oval of track you get one pair of feeders for the whole oval. But if you try to do that with a larger layout you'll probably run into trouble for two reasons:

1. Voltage drop, as mentioned before. The resistance of nickle silver rail is much greater than that of copper wire, so over a short distance of rail the voltage will drop enough to slow your trains.
2. Rail joiner problems. Rail joiners are designed to hold two rails in place and to pass electricity between the rails. However, over time some joiners will loosen or get dirty and eventually provide an imperfect connection. This will lead to even greater resistance (see point 1) or loss of connectivity altogether.

Now, this doesn't mean that every layout without power buses experiences rail joiner problems or large voltage drops. There are real life examples of layouts with long stretches of track where power is passed only by rail joiner and things seem to work well. However, in my experience every layout that relies on rail joiners for electrical connections has evenually experienced power drops. And this is why the power bus method is so widely recommended.

So, you may ask, we need to add feeders to the rails every few feet, but exactly how many feet apart? This is a matter of frequent debate on the model railroading internet forums. At one extreme are those who argue that rail joiners can never be trusted and thus each rail must get its own feeder. Not quite as extreme are those who argue feeders should be 3' apart, but don't require a feeder per rail in instances (like switch ladders) where many separate rails are used in a 3' span. At the other extreme are those who argue that spans of 10' or more are okay between feeders.

After reading what everyone said and thinking about my own experiences I tend to agree with those who don't see rail joiners as a long-term solution to connectivity, but I also don't see it necessary to space feeders every 3'. So, I decided to connect the feeders at every other rail joint. That is, feeders are attached at the rail joint, so every rail has a feeder, but there is only one feeder per two rails. This saves time and resources.

Alas, no solution is without controversy. By soldering the wire to the rail joint I am also soldering the rail joints, which is another big debate topic on the forums. Some argue that joint soldering causes problems because the metal rails will expand and contract with temperature changes. Soldering inhibits expansion, thus on hot days the rails will eventually bend out of gauge somewhere as a result. Others respond that they've never had this problem despite soldering their rail joints, and I'm in that camp. I solder all curved flex track joints and half of the straight ones, and in 2.5 years I've had no problems. I suspect there are as many as three reasons I've been so lucky:

1. The temperature variation in my room is not extreme -- from 60F to 85F at the limits. Even on our hottest days the room doesn't exceed 85F, and if it ever does there is a room A/C that is available, albeit almost never used. I suspect people who see problems often see greater temperature swings.
2. This is a very dry area, without great swings in humidity. Humidity doesn't affect the metal rails, but it can affect the roadbed and subroadbed depending on the material used. I have heard from many sources that Homasote -- a popular roadbed especially amongst those who hand-lay track -- is especially susceptible to contraction/expansion with humidity changes. It may be that the expansion/contraction problems some people are seeing have more to do with the roadbed than the track.
3. N scale may be less susceptible than HO and larger scales. I'm not married to this idea, as the rail sizes between the two gauges aren't that far apart (my code 80 in staging is not that different than code 83, which is the most common for large HO layouts). On the other hand, the track width for N is just over half of HO, and that might make a difference. However, for whatever reason I've noticed that it's rare for an N-scaler on an internet forum to complain about soldered joints causing track bendage due to expansion.

So, to make a short story long, I connect feeders to every other rail joint. Here's an example from the current staging construction:


As I keep mentioning, in staging looks don't matter. In fact, I personally like to have all the behind-the-scenes construction and wiring details visually evident in staging because visitors often find that stuff just as interesting as they find the sceniced portion of the layout. So, in staging I solder the feeder wires to the outside of the rail joint, thus avoiding potential problems with the wheel flanges hitting the wire on the inside of the rail. I'll describe the detailed procedures for soldering wire to rail, both for staging and the main layout, in more detail in a future post.

So, this post concludes the standards used on this layout to get power to the track under most circumstances. There are, however, a couple of exceptions yet to discuss. One is auto-reverse sections, and the other is track wiring for switches with "live" frogs. My next wiring post will cover auto reverse. I'll hold off on the discussion of switches with "live" frogs until I get back to construction on the main layout, as this doesn't apply to the Atlas code 80 switches used in staging.

Wiring standards part 2: Terminals and Feeders

The first wiring post covered power cabinets, power districts, and power buses. Now that we've got power to the underside of the layout in the form of the bus, we now need to get it from the bus to the track. The wires that connect the track to the bus are called feeder wires or just feeders.

Later in this post I'll discuss the standards I use for attaching feeder wires to the track, but the first question I want to address is how to attach the feeders to the power bus. There are two basic approaches:

1. Directly connect each feeder wire to the bus wire of the same color (i.e. same polarity). This makes sense for layout areas where track is sparce, such as a single track main line on a shelf. In such cases there aren't a lot of feeder wires so a short, direct feeder connection is best.



2. Connect all local feeder wires to a terminal that is attached to the power bus. This makes sense where track density is high. The staging area on this layout is an example of just about as much track as you can squeeze into a given area. In this case you simplify the wiring by connecting feeders to several central terminals.

There are other published wiring methods, but these appear to be the most commonly used. On this layout I use the terminal method predominantly, and the direct connect method in places where track is sparce.

An example of a terminal used on this layout is shown in the photo below. This picture illustrates the various wiring standards in practice:



There are many things to note in this photo. First, the terminal strip itself is an 8-slot barrier strip that I buy at Radio Shack for about $3 each -- cheaper than I've seen elsewhere. I don't say this is the best choice for this application, but it's the best I've found available and the price is good.

Second, note the power bus. This is the pair of 14 gauge wires near the top of the photo, one red and one black, that each weave through 4 of the slots on the terminal strip. It's a bit of work to strip that much 14 gauge wire and snake it through 4 terminals, which is the one drawback of this method. If you use this method be sure to use solid, not stranded wire for the power bus as it's much harder to do the same thing with stranded wire.

Note also that on the left of the terminal strip you'll see a label on the power bus wires -- "PD-1". This means "power district 1", per the standards discussed in the first wiring post.

Third, under the terminal you can see a label "1-J". This means power district 1, terminal J. By convention, terminals on a power district are named A, B, C, etc., with A being closest to the power source, B next closest, and so on. This convention is not a guarantee, as future layout revisions may result in, for example, a new terminal "P" inserted between terminals "C" and "D".
Fourth, you'll see smaller red and black wires connected to the wiring screws on the bottom side of the terminal. These are feeder wires. In general the feeder wires are on the side of the terminal that is most accessible given the location of the terminal.

Feeder wire conventions are as follows:

1. Wire is 22 gauge, red for attaching to the red power bus, black for black. 22 gauge is large enough to carry the power the short distance to the track, and small enough to easily work with when attaching to a rail. I prefer solid wire but I use stranded when solid is not available. I avoid buying "hobby" wire because it is incredibly expensive, instead buying the large spools from Radio Shack. Unfortunately you can't specify color when you order, and it is important to have an equal amount of each color, so instead of ordering in advance I just pick up a few extra spools when they have some in stock.


2. Feeder wire pairs are twisted in order to keep them together for easy tracking (feeder wire distances are so short that you don't have to worry about impedance).


3. The twisted pairs are stapled to the layout wood to hold them in place with a T20 (narrow) or T50 (wide) stapler, depending on the specific situation. I am careful to use long staples (1/2" or more) to avoid the staple damaging the wire itself.
   
4. Each wire pair has a name. For example, 1-J-3 means power district 1, terminal J, wire pair #3. The track location to which a feeder wire pair is attached is noted on a Visio diagram along with the name of the wire pair. (I'll post a sample of the Visio diagrams sometime in the future.)


5. Wire pairs are labeled with their name, usually dropping the power district as that is obvious by the location of the wire. So a typical label might be "J3". There should be at least two labels per wire -- one near the terminal and one near the track.


6. By convention, feeder wires are attached to one of the 4 terminal screws for their wire color according to the following pattern: From left to right, wire 1 goes to the leftmost screw, wire 2 to the next, 3, 4, then wire 5 back to the left most and so on.


7. I try to keep to a limit of 12 feeder pairs per terminal, which equals 3 feeder wires per terminal screw. If more are needed then another terminal should be added. This means that the screws, from left to right, would have the following wire numbers: 1-5-9; 2-6-10; 3-7-11; 4-8-12.

The next wiring post will discuss attaching feeders to track.

Wiring standards part 1: Power

I've built (or more accurately, partially built) 5 previous indoor layouts, 3 in HO and 2 in N scale. I learned a lot from each one, but they were all small, varying in size between 32 and 44 square feet. On this layout I've found that there are some things you won't learn until you build that big layout, and one of them is how to set up a well-organized wiring system. As I've reached the point in the staging reconstruction where wireing is added, now is a good time to start describing the system. This topic will take a few posts.

When I started this layout I took my first shot at a wiring system, and a lot of things did go well. I set standards for the type of wire used for each purpose, developed a system of a track power bus with terminals and feeder wires, labeled each wire per a naming system, and diagramed it all in Visio. I consider it a good first effort, but as I'm redoing staging this is a good time to revise the system with the lessons learned.

Some of the changes being made are due to things I learned in the process of doing, and some due to things I read in books or on-line forums that caught my attention now that I'm actually wiring a sizable layout.

Note that this is *my* system, not a general purpose one. There are all kinds of details that were chosen to match my layout's specifics, such as it being N scale or the use of Digitrax DCC. At a later date I'll probably post on how/why I made those decisions, but for now those are just the givens that influenced the wiring design.

Power Cabinet

It all starts here. You want to have a cabinet that contains your power supply, your DCC command station, booster(s) (if needed), and any electronic equipment that can be kept centralized, like the power district units, in one location. This is partly for ease in problem debugging. It also helps to have it all in one enclosed cabinet to keep out dust, etc. The other point is that you want to minimize the wire length of the power bus from your power station to the most distant track. (I'll explain why shortly.) So it 's a good idea to put the power cabinet in a central place to keep the longest power bus length to a minimum. On my layout I'll put the cabinet under the lower deck, on the west wall just north of the stair case.

(Aside: What do the terms DCC and DC mean? Think of them as digital (DCC) and analog (DC). DC is the way model trains are traditionally powered, that is by a transformer that sends Direct Current (DC) to the rails and the locomotive speed is determined by the amount of power received. DCC is Digital Command Control. For DCC the system provides AC (Alternating Current) to the rails in a constant high voltage, and uses the rails as a digital bus to send electronic signals. Each locomotive is equipped with a decoder to interpret the signals, and each locomotive is assigned an electronic address. In this way the decoder is told by the DCC command station how much power to route to the electric motor, or how to operate lights, or what sounds to emit, etc. DCC is more expensive when you consider the cost of just running trains, but it has enormous benefits in terms of simplifying wiring and operations and the use of features like sound and lights, as well as the obvious benefit of running multiple trains without any extra effort. The large majority of sizable layouts use DCC these days. I'll post more about DCC and DC sometime in the future.)

Power Districts

If you spend any time on model railroading forums that include DCC as a topic you'll hear old timers advise you to set up power districts. This is not a lot of work, and in a room sized layout it makes sense.

A power district is not the same as the "power block" concept from DC cab control, although in both cases what you are doing is taking a section of track and electrically isolating it from the rest of the layout. However, a power district covers a very large area -- on a DC layout you might have a power district comprised of many power blocks. The power district idea is this: it's common for an electrical short to occur on your railroad, most typically when a locomotive derails and a metal connection is made across both rails. When a short occurs your DCC command station will sense it and shut down power before anything burns out, and with Digitrax an audible series of beeps is emitted. At that point everthing stops until you find the source of the short. In a large layout such a search can take a long time, meanwhile everyone stops and waits.

The solution is to divide the layout into electrically isolated power districts, each with its own short-sensing circuit breaker. The size of the district is up to your personal tastes. For me I'll probably have 8 districts, 4 per deck, with the south staging room being one district on each deck.

(If you are running scales larger than N you may find, depending on locomotive density, that you need multiple power boosters. Each power district can receive power from only one booster, so you power district size may be constrained by your booster setup. This is, in practice, a non-factor in N since our locomotives don't require much power..)

You can set up your track at installation time with the insulators or rail gaps in place to provide for power districts, but not actually add the circuit breakers until later.

The power district management components will be resident in my power cabinet. Digitrax provides a PM42 for this purpose, but it does not get good reviews on the internet Digitrax forums. I have one PM42 and I have to say I understand the complaints -- it's requires a complex set up and tuning it can be a challenge. This component is part of general electronics, not specific to your DCC manufacturer, so I don't have to use the Digitrax product. I'll research this later and report the results here. A likely candidate is the Power Shield from Tony's Trains.

Power Bus

For each power district you'll have a power bus, consisting of two wires, using your largest wire gauge, that runs the length of the district under the layout.

I've chosen to use 14 gauge solid wire, red and black, for the bus. The wire size is influenced by two things: 1) the peak current (amperage) you expect to draw on the district at any one time, and 2) the length of the wire.

For (1) you can calculate the amperage by figuring how many locomotives you'll run and what their likely amp draw will be (some recommend using the stall current). This can be hard as so many variables are involved. However, one of the nice things about N scale is that locomotives, especially those manufactured this century, are amperage misers. We typically rate them at 1 amp maximum but rarely do they ever get close to half that (even most HO motors don't hit 1 amp at stall current). For my layout , despite a prevalence of track and locomotives, I am going to try using a 5 amp Digitrax command station for the whole thing and based on comparisons to similar layouts I don't think there will be a problem. If I do have a problem I'll have to get a separate Digitrax 5 amp booster for the upper deck. Because of the 5 amp limitation I used the value "5 amps" for my wire gauge calculations.

For (2), the issue is resistance. The longer the wire, the more the resistance. If the resistance gets you high you'll get voltage drop and the locomotives drawing power near the end of the bus will run slower than those close to the power source. However, you can counter this with a thicker wire gauge, since thicker wire has less resistance. (Note that wire resistance is not like the width of a water pipe. That is, if you have 20' of 2" pipe and 1' of 1" pipe, the maximum water flow is determined by the smaller pipe, and all that wider pipe makes no difference. But with wire resistance, as short length of small gauge wire, such as the feeder wire between the power bus and the rails, does not contribute appreciably to the overall resistance of the wire length.)

So, get your amperage, get the length if wire, then look up what size you'll need in a table to avoid the voltage drop problem. There is probably such a table on line somewhere, but I've found that no two sources of info on this are alike, due the the variables involved. For example, the table on page 104 of Andy Sperandeo's book Easy Railroad Model Wiring tells us that for 20' and 5 amps use 14 gauge and for 30' use 12 gauge (larger numbers mean a smaller wire gauge). However, another Model Railroader book, Mike Polsgrove's DCC Projects & Applications, says on page 13 that if you have a 14 gauge bus you won't need to consider 12 gauge unless your run is longer than 80'. Same publisher, different info. Part of the difference may be that Andy's book is about general electrical topics, with DCC covering only one chapter near the end, and Mike's is focused solely on DCC. As a test I ran trains on track that was about 75' from the power source, with 5 locomotives running at once, and there was no evidence of voltage drop. So since in practice my longest bus run will be about 40' 14 gauge should be fine.

I've been using 14 gauge solid (not stranded) wire, one red and one black.

I buy the 14 gauge wire (solid, not stranded) in red and black colors from the electrical section at Home Depot. You won't find this gauge at many hobby or electronic stores, and in any event it's cheaper at Home Depot because they sell it in large bulk to electricians (14 gauge is commonly used in houses for wiring circuts for lighting and common outlets).

When installing the power bus I now twist the red and black wire together. This is because if you have two parallel wires over a distance a nature impedance will form that can cause interferance with your DCC system. The twisting prevents that.

I use a cheap Dymo LetraTag label printer I got at Target to create labels for the power bus and wrap the labels around the twisted wire pair, usually adding a layer of scotch tape on top to assure that the label stays in place. For the buses the label is of the form: PD-1 (for Power District-1). I looked at various products designed for adding number tags to wires and found this to be a cheaper solution if you expect to create a lot of labels -- and they also look nice.

The next post(s) will cover my wiring standards for actually getting the power from the bus to the track. Later I'll discuss auto-reversing wiring standards.