Wiring Basics


There are other subjects we feel you should know about the electrical apparatus that you will need to consider when building your first model railroad, these are covered here.

DISCLAIMER: The article that follows will include brand names as a reference only. Neither we who are writing these pages nor the NMRA intend for these brand names to be a recommendation on our parts. In some cases, the manufacturer may no longer be in business or may not be manufacturing these particular products. We leave recommendations to the owners of your local hobby shops or your friends who are model railroaders.

NOTE: The following is Part 2 of a series of articles written by Roger Hensley and published in Model Railroad Craftsman magazine in 1985 on Beginning Model Railroading. The article is reproduced here with the permission of both the Author and the Publisher and has only been edited in two places.

As you begin to expand your layout, you may well run up against the problem of a lack of power. A starter set power pack seldom has an excess of power to begin with, and in some cases doesn't have the protection a circuit breaker provides against burn-outs. Many train set locos have an inexpensive motor that doesn't draw much power, but then they don't have the pulling ability of many of the other locomotives that you can buy that have the better motors. A power pack that says it can run two or three average trains really does not mean much. What is average? What kind of current draw will the pack provide? That's a much more realistic measure.

Any typical Athearn locomotive comes close to being an average engine for choosing the needed power pack rating. It is likely that you will own at least one of their engines at some time in the future, so they make a good guide to measure against. An older Athearn diesel will pull somewhere around a half an amp with a train behind it, and it will pop the breaker or burn out an unprotected pack that can only supply a quarter of an amp safely. Are you going to run all the lights and switch machines off the same power pack that you use to run your trains? Then you need a larger capacity power pack. I always suggest using separate power sources for the accessories. After all, it's no fun to watch a train slow down or jerk every time a turnout is thrown while the train is running. Get at least a one-amp pack; two amps is even better.

There are several manufacturers of what might be called "traditional" plug-it-in and wire-it-to-the-track power packs. There are also companies that make power supplies, throttle kits and command control systems. To simplify things, I am going to use one line of packs to demonstrate some of the points that I feel you should know about power packs. This is not meant to favor them over other brands. Regular power packs are made by Model Rectifier Corporation, Tri-Tec, Rix, Starr and SRT; go to a hobby shop and look at all of them, since each company and each pack has its own special features. The Rix unit is a walkaround throttle, SRT has one main pack and a walkaround addition, and MRC and Tri-Tec have extensive lines of power packs of different sizes and with a variety of features. The example we will use here is the Model Rectifier Corporation line.

MRC has packs that start with light "plain Jane" basic units and runs up to solid state electronic throttles. The simplest of power packs is not much more than a rectifier to change AC (alternating current) to DC (direct current), a transformer to drop the voltage, and a rheostat, which is a variable resistor to change voltage and control the speed of a train. A circuit breaker protects the unit by opening the circuit when too much current is drawn from the pack. The output terminals are generally low-voltage AC for powering lights, switch machines and other accessories, and variable DC for the track. Simple and clean. There are various power (amperage) ratings available for such "standard" packs.

The next step is to take a pack and add a switch for "Pulse." In a pulse throttle, half the AC wave cycle is used to produce a rapidly pulsating DC; a switch controls whether this is on or if the regular rectified current is used in the output. A good example of this throttle type is the MRC Throttlepack 501, which is a strong pack delivering 1.9 amps and has the pulse option. The reason for the pulse feature is better low- speed control, and it does work. In a sense, the pulses "push" the motor armature to help overcome inertia and friction. However, there is a fly in the ointment. The half-wave pulses cause extra heat to build up in the motor. Too much of this heat can cause the motor to burn out; some types of motors are more susceptible to this than others. While this isn't that common a problem, you should be aware of it. Pulse power should not be used for high speeds (it isn't needed there), and any loco that runs too hot may have other problems as well, (lubrication, tight gears).

These "standard" packs can be found as single and dual packs, the latter with two control knobs and two track outputs. Some use a common transformer and rectifier, and others separate them. You will have to make your own decision about dual-control packs. To be honest, a better argument can be made for those with single controls.

Solid state packs
Now we come to the reason that I used the word "standard' to describe the first type of power pack. Electronic, or solid state, packs are now available. The quest for better low-speed control has brought us to a new era. Since prototype locos don't jump from a standing start to a hundred miles per hour, neither should our models. One solution is to use heavier locos with flywheels to smooth out starts. Another is to use electricity creatively. In essence, solid state throttles put out a spike of power to get the motor turning. The spikes increase in frequency until the motor is being fed straight DC at higher speeds. Changes in the throttle setting bring in the spikes again until the new speed is reached, when they are merged into smooth DC MRC's Tech II series power packs are an example of this type of pack. Tri-Tec's are in the solid state category, too. These packs really do provide smooth slow-speed operation! MRC calls their circuitry for doing this "proportional tracking control" and their Railpower 1400 produces 1.2 amps and Railmaster 2400 1.65 amps. These are single packs. Again, I urge you to check at your hobby shop and look at the packs from different manufacturers.

You can get meters to monitor locomotive performance, DC expansion terminals to power hand-held walkaround throttles and radio-controlled throttles. Various forms of command control will let you run two trains independently in the same track section, too. As you can see, power packs can be found to fit nearly any need and come in a wide price range. If you don't find what you need in a catalog, you can build throttles.

- Click for larger graphic - NOTE: Walkaround throttles and radio-controlled throttles add realism to the operation of a model railroad as they allow you to follow your train instead of just stand in one place and watch it run. They also make the operation simpler as you are right there with the train when making switching maneuvers instead of the need to walk back and forth from the train to the fixed throttle. As an example, our Track Plan #3 would be much easier to operate with walkaround throttles than fixed throttles as there are actually 3 different areas of operation.

There is another feature that comes with some of the electronic packs, and that is "momentum." Momentum simulates the starting and stopping action of a real train automatically. You can turn your throttle up to the setting you wish to operate at and the train will slowly begin to move and gradually increase in speed until it reaches the speed you have set. Stopping reacts the same way slowing gradually. Most packs have a brake switch to let you come to a stop more quickly than by letting it "coast" to a stop. It gives the feel of operating a heavy train that takes time to get rolling and can't be stopped quickly.

NOTE: Since Roger Hensley wrote this article, DCC has come on the market and been standardized. Rather than discuss DCC here, we invite you to read the pages in this section of the NMRA Web Site on that subject. You can see those pages here.

Those who have ever wired a tinplate layout recall that they just plugged the track together and the trains ran. That was possible because the trains were powered by alternating current (AC). HO scale trains run on direct current (DC), and that creates the possibility of shorting out the track by improper wiring. The oval within an oval presents no problem. But, when you install turnouts so that the train can go from one to another or may be reversed by going around a loop and then back onto the mainline, you have to make electrical adjustments to avoid a short and make the whole operation come to a halt. The answer is to isolate sections of track and the rails electrically This is also the way you create control block sections for running more than one train and separate sidings so that they are electrically "off."

- Click for larger graphic - Turnouts are track, and switches are electrical. That's the way to avoid confusion from the terms. Atlas has an entire line of control switches that can select direction as well as turning the different track sections on and off. The Atlas layout plan books use their products and show how to wire the layouts with them. Your hobby shop also has a number of books on wiring.

To turn a siding on and off, all you have to do is insulate one rail with the plastic rail joiners that are available and add a wire and an on-off switch in it, being sure that you wire back to the correct side of the power pack. The standard way of wiring model railroads is to have the positive on the right hand rail when the loco is going forward. Just put the leads on the track so that the engine moves forward and to the right when the direction switch on the power pack is to the right. Swap the leads on the back of the pack if you need to. The plastic rail joiners take the place of the metal ones when you need to insulate a rail. Both ends of a siding need to be insulated if it is double-ended and returns to the main track. If it is a dead-end siding, all you need is one insulator. If you have several sidings that you wish to isolate, as in a yard, merely insulate one rail of each siding and add wires and switches to turn them off and on. The points where the insulated joiners are used are called gaps.

- Click for larger graphic -

One way of wiring a railroad is called common rail. What you do is always insulate the same rail, leaving the other one connected. Sometimes you have to jumper wire around a turnout frog and gap to do this. Take a sketch or drawing of your layout that shows both tracks and mark the outside rail as "plus" and the inside one as "minus." You can see that, in the case of an oval, the outside rail will always be positive wherever it goes and the inside will always be negative. If you insulate the inside rail on every siding, including those that will be controlled with on-off switches, the outside rail will be like a common ground. The inside rail becomes like a switched hot lead. This is what makes this "common" rail.

You can use two different power packs with this system to control different parts of the layout at the same time if they are insulated from one another, as in the case of an oval within an oval, as long as there is an insulator at the point where the two connecting turnouts join. Each pack will need one wire to the common rail, with the other wire going to the insulated rail of the oval and/or sidings to be controlled. One advantage of the common rail system is that it allows you to easily "pass the buck" with control from pack to pack on locos that pick up power from the right side of the front truck and left side of the rear truck. Without the common rail, these would see the insulated joint as a switch that is turned off and stall. Locos that pick up power from all wheels, though, may surge faster momentarily when they receive double power as they cross over the joint. There are other ways to handle this, but this will get you running. More detailed explanations of the alternatives may be found in books.

- Click for larger graphic - The only place that you heed to double insulate is where you are going to turn the locomotive back to the main track pointed in the opposite direction; remember, positive and negative have to be kept apart, and they also control direction. Double insulating, that is insulating across both rails, is needed at reverse loops and wyes. You will need a switch to control the direction of the train in the loop as well as one to change the direction of the main track while the train is in the reversing section. You can use your drawing to check this out. - Click for larger graphic - When you reverse the track back onto itself, the positive rail that you are tracing will suddenly run into a negative rail. You can readily see where and why an insulating gap and plastic joiner is needed. The reversing leg of a wye or loop will always need two wires to it, as you want to isolate it completely from the common rail. The switch needed is a double-pole, double-throw type (DPDT), rather than a simple on-off (single-pole, double-throw, or SPDT) type.

- Click for larger graphic -

One quick point about flexible track and insulators. Since there are no notches for rail joiners on flexible track as there are on sectional track, you could end up with a bump where the insulating joiner is. The plastic ones are thicker than the metal ones and you should allow for this. I cheat. I break off the ends of the ties just where the plastic joiners must go, leaving the other side of the ties intact. If the spot shows, I glue down some pieces of tie to hide the gap. A touch of paint hides the plastic rail joiner's color. An alternative way of placing the insulating joiners on flexible track is to take a knife and notch out under the rail. Click for larger graphic

Note: The wiring of a wye can be dependent upon the type of turnout used. Most beginning layouts (and even the more advanced) use a turnout with a 'dead' frog (the place where the rails cross) or one that is isolated and changed electrically by switch machine contacts when the turnout is thrown. The above drawing works for that type of turnout. However, there are turnouts where the frog may be solid with the rails. Those turnouts require that both rails be insulated on all legs of the wye as in this drawing by Paul Templar.

To close off this discussion for now, I want to include the reminder that AC is for accessories, not connecting to the track. This is one of those things you are "supposed" to know, but can easily forget. Just make sure you don't tie so many accessories to your power pack that you rob power from the trains. Consider one power pack for the track and one for accessories only.

All of this discussion about electrical control will mean very little if the rails are dirty, stopping the power from reaching the locomotive. There are a number of methods that can be used to clean track.

One of the first things that you may run across is a track cleaning car that uses some kind of liquid to clean the rails. The car is meant to be pulled around by a locomotive or run in a train, cleaning off the dirt and oil that may have accumulated. Most people overfill these cars, leading to a lot of fluid spilled and wasted and making more dirt than they had in the first place. If you use one of these cars, start off with only a little fluid to begin with. You can always add more and will avoid getting it where it doesn't belong - all over the scenery! Several manufacturers have these cars: AHM, Life-Like, Walthers and more. Bachmann has a powered track cleaning car that is a model of a prototype track inspection car. All the above are HO scale.

These cars have a small tank and a pad that rubs on the rails. Using them frequently will insure that this method is effective, but oxidation on brass track will not respond well to this treatment. You need something to break through the coating.

This brings us to another method of cleaning that is an old standby and that you will probably use if you stay in the hobby long enough. It is a small hand-held bar that looks like a gritty eraser. While they are made by several different companies, the best known is probably Walthers' Bright Boy. The bar is rubbed across the tops of the rails and burnishes them. It does a remarkably good job and even takes off dirt, oil spots, paint and thin plaster drippings from scenery work. Yes, you can use 400 or 600 grit wet-or-dry sandpaper, but the Bright Boy is better, less abrasive and sized for the task. Never use steel wool to clean your track or wheels, and don't be tempted to paint steel wool green or brown for bushes, either. Steel wool leaves little flecks of steel that will be drawn to the motors of your engines.

The only suggestion I have after using a Bright Boy is to consider vacuuming the track afterwards to pick up the little specks of abrasive and dirt. You might also consider rubbing the rails lightly with, believe it or not, hair clipper oil or another light oil that is plastic compatible. The Wahl brand is the modeler's favorite and it is available at some hobby shops or through barbers supply houses. It inhibits oxidation and improves contact. An article about this was in the June, 1981, RMC.

Also in the dry track cleaning category is the Virnex (former Stewart) track cleaner that fits over the fuel tank on an Athearn SW1500 switcher. This is an abrasive pad type of cleaner. The advantage it has is that it can rest of a shelf while the switcher is in everyday use, but can be slipped on in a moment for track cleaning. Again, the clipper oil treatment would be in order after its use, just as after running the Model Die Casting track cleaner car that is based on their boxcab diesel. This unit has four abrasive discs at each corner.

Liquid or dry hand-held or powered, clean track can be achieved. It is worth doing when you see the trains roll smoothly.

Back To: Beginner Main Page

Page last updated December 2, 2014