Easy-To-Understand Wiring Basics and Atlas Electrical Controls

If you are a beginner, Atlas will have you wiring a layout, with ease. Yes, there is a lot to know about electrical terms, techniques and wiring, but Atlas helps you learn what you need to get your layout running. We make wiring easy to understand and follow. Some definitions and explanations below will start you on your way to understanding the Atlas electrical control system. For additional information, The Complete Atlas Wiring Book (below), has everything you need to know about wiring with Atlas' electrical controls. After reading this book, you'll be pleasantly surprised how easy wiring is once you have the electrical knowledge you need.


#12 The Complete Atlas Wiring Book

This is a user-friendly book that makes the Atlas electrical wiring system easy to understand. It introduces beginners to the most basic principles of common rail layout wiring, and takes advanced modelers through complex wiring operations. Learn how to install and use our quality components on any layout. There are over 100 diagrams and a complete glossary.


F.Y.I. - The most important electrical circuit in any layout is the one supplying the power to the locomotive, making the train operate. It consists of a power pack, wires, track and locomotive. Trains operate when electric current flows from the power supply to the motor in your locomotive. The media used to transmit this current are the track itself, wire, terminal section and/or terminal joiners. With terminal track, current is delivered by attaching wires from the power pack to the screw posts. Terminal joiners have their own wires attached, which can be easily connected to any power pack.

If you'd like some explanations of various wiring terms, please click here to view a wiring glossary. These and many other terms are highlighted in the Complete Atlas Wiring Book shown above.


Beginning with the Basics

Chapter 1

The basic principles of layout wiring begin with a simple oval and single train operation, shown below.

Speaking of principles, wiring belongs under the layout, not on top. In the following paragraphs, you'll learn just how to accomplish this by mastering the techniques used by expert modelers. Remember, the only difference between experts and you is that they know how, and you will too after reading The Complete Atlas Wiring Book!

The Four Parts of Layout Wiring


1. Track:
Trains operate when electric current flows from the power supply to the motor in your locomotive. The medium used to transmit this current is the track itself, wire of various sizes, terminal section and/or terminal joiners.

Electrically, the rails act as two wires to carry current to the locomotives. Because the rails are large compared to actual wires, they are adequate for carrying this current. Since layouts are made with more than one piece of track, rail joiners must be used to connect track pieces. Metal rail joiners hold two opposing rails in alignment and carry the current from one rail to the next. To prevent loss of voltage, the joiners must be clean and fit tightly on the rail.

If the rail joiners become bent or loose, the situation shown below may result. Here, the train runs fast when near the terminal track section, but slow on the other side of the loop. In this case, all loose rail joiners should be replaced with new rail joiners.

The illustration below shows that the electrical contact between the rail and the metal wheels of the locomotive must be good. Wheels and rails, which eventually get dirty during operation, must be cleaned regularly with a track eraser to restore smooth operation and successful electrical conductivity. Never use abrasives such as sand paper or steel wool as these will damage the track.

Terminal Track and Terminal Joiners: The most common method of providing electric current to the track is with terminal track or terminal joiners. Terminal track, which can be straight or an 18" radius curved section, is a piece of sectional track with electric contacts and screw posts molded in. Current is delivered by attaching wires from the power pack to the screw posts. The illustration below shows the position of the wires and contacts to the rail of a terminal track.

When securing wire to a screw, bend a loop in the wire in the clockwise direction as shown below. The tightening of the screw will pull the wire into place.

To avoid loose ends, stranded wire should be twisted tightly before forming the loop. It would be best to tin the ends of the wires with solder before forming the loop. The tinned wire will hold its shape better than untinned wire.

Terminal joiners, which are metal rail joiners with wire crimped or soldered to them, are preferred means of delivering current to the track. They are much less obtrusive than terminal track and a lot less toylike. (See below) Once the track is ballasted, it is almost impossible to see the terminal joiners.

Wires from the terminal track and terminal joiners should be fed through small holes drilled in the table top. Do not solder wires directly to the track. The heat of the soldering iron may distort or damage the plastic ties.

2. The Power Pack:
HO, N and O scale model railroads operate on low voltage for safety reasons. Locomotives need a power source of 12V DC. In addition, you need a way to control the output voltage to the track to control speed, as well as means of reversing the polarity on the rails to control your locomotive's direction. A power pack combines all these elements in a single unit.

The power pack is the device which plugs into the normal 110V wiring in your home, has a throttle to control speed, a reversing switch to control direction and two output terminals which connect to the track. It also contains a transformer to lower your home's 110V to 12V and a rectifier to convert AC to DC. Better power packs contain overload protection such as circuit breakers, which prevent a short circuit on the track from damaging the power pack.

In addition to a variable DC output, power packs have a constant-voltage AC output terminals to supply power to operating lamps, switch machines and other accessories. This allows your accessories to receive the proper amount of power, regardless of the setting of the throttle. Since some accessories require considerable current, especially switch machines, (except for temporary set-ups or very small layouts), it is better to provide a separate AC transformer to power accessories. That way, a sudden demand for current, as when a switch machine is thrown, will not affect your train's speed.

Today's power packs come in many sizes and varieties. They can be single units for one train or may have dual or multiple controls for two or more trains. In general, a separate power pack for each locomotive is best and that's what we will show throughout this book. While newer dual-throttle power packs are usually satisfactory, some earlier ones have internal wiring which preclude the use of the common rail wiring described in this book.

3. Wire:
All model railroad wiring may be done with small, low voltage wire, available in hobby shops, hardware and electronic outlets in a variety of sizes. The size (diameter) of wire is expressed by a number. The smaller the number, the larger the wire. Common house wire is No. 12 or No. 14. In most cases, No. 18 or 20 wire are quite suitable to conduct current to the track. Very large layouts require larger wires.

Wire is of two types, solid and stranded; the latter consisting of many smaller wires twisted together. Stranded wire is easier to work with and it is considerably more flexible and less likely to break upon bending. A broken wire inside insulation, where it is not visible, can be quite frustrating. Stranded wire may be purchased tinned or untinned. Tinned wire costs more, but it makes soldering easier.

Soldering is the most reliable method of joining two wires and is much easier than you might think. The techniques are easy to master and necessary tools are few and inexpensive.

A soldering iron or gun of 25-30 watts is sufficient. The tip of the iron should have a chisel shape, which is effective for wiring. The solder should be solid. Follow the recommendations of the vendor for the best type to use for small wiring. Flux is used to make the melted solder flow easily. A rosin base flux is best; never use a flux that is "acid" in composition. Note: Today's solder is manufactured in varying mixtures of tin and lead. The most commonly used mixture is 60/40 (60% lead/40% tin), and comes in varying diameters. Solder is also available pre-fluxed, so the application of flux to the rails or wire may not be necessary.

A small file is useful to dress and clean the tip of the cold soldering iron. When soldering, keep a damp sponge handy to wipe off the tip of the hot soldering iron and keep it clean. Occasionally, it is necessary to solder a connection close to other soldered joints. Use metal spring clamps as handy heat sinks to keep other joints from coming unsoldered.

4. Locomotives:
Some locomotives operate by a third rail and have AC motors. Today, most scale model railroad locomotives have a DC motor and use two running rails for power. The material in this book is confined to DC two rail operation. Because one running rail is positive and the other negative, they must be insulated from each other to prevent a short circuit. That's why model railroad ties are made of plastic, which serves as an insulator.

To prevent the wheels and axles from acting as short circuits, at least one wheel on each axle is insulated. Since the motor in a locomotive must be connected to both rails, at least some of the wheels on each side must be metal.

The figure below shows three common arrangements for model locomotives. The drawing on the upper left shows one truck with metal wheels on one rail and insulated wheels on the other. The second truck is just the reverse. In this case, the motor may be connected between the trucks.

If there are only four wheels, as shown above, the insulated wheels can have metal rims and wipers sliding on the rims to connect the motor to that rail. Such pick-up could be added to each truck of a two-truck locomotive, doubling the number of wheels being used to contact the rail. This is standard on ATLAS locomotives and most of the better quality locomotives. More pick-up wheels reduce the possibility of a locomotive being stalled by dirty track or wheels.

If a steam locomotive has a tender, all the metal wheels on the locomotive can connect to one rail as indicated above. The tender must be insulated from the locomotive.

Model locomotives use permanent-magnet type motors because the direction these motors rotate depends only on the direction of current through the motors. By controlling the polarity, (+ and -), of the rails, you can control the direction of the locomotive. The National Model Railroad Association (NMRA), has set a standard that locomotives move so that the positive rail is on the right.


Locomotive Direction for Various Rail Polarities

"Direction of motion" in model railroading terminology, does not refer to the direction in the locomotive is facing since locomotives can be moved forward or backward on your layout. In the bottom two blocks, the polarity on the rails has been reversed so the locomotive in these blocks moves to the left. A modeler may accidentally reverse the wires in the locomotive, causing opposite operation. This must be corrected immediately to prevent confusion.


Steps To Successful
Electrical Wire Soldering

You'll find the act of soldering takes less time than it takes to read these instructions! First you must tin the soldering iron, then tin the wire.

*BE CAREFUL! A soldering iron can cause burns or start fires if left unattended.
*CLEAN the tip of the cold soldering iron with a small file.
*HEAT the iron and apply flux. Apply a small amount of solder to the iron
to cover the tip. (This procedure is called tinning.)
*TWIST the ends of each stranded wire to be soldered, so no wires stick
out. If the wire is not pretinned, proceed to tin the wire by dipping the ends into the flux paste and touch them with the tinned tip of the soldering iron. The hot solder will flow from the iron to the wire. Copper wire will take on a silvery sheen as the solder flows.
*REMOVE the heat and let cool. The wires are now tinned. (If you use
pre-tinned wire, this step is not necessary.)
*CLEAN the tip of the hot iron with the damp sponge and re-tin. When
cool to the touch, take the two wires to be joined and lay them side by side in your hand with the ends even. Twist the tinned ends together as tightly as possible.
*DIP the twisted ends into the flux paste. Touch the hot tinned iron to the
twisted wires until the solder flows and unites the wires. You may need to apply more solder.
*REMOVE the heat and let cool. Don't move the wires until the solder
solidifies, usually after several seconds.
*FOLD the joined wires back on themselves and cover with electrical tape.
*UNPLUG the soldering iron upon completion of soldering.

The plastic insulation covering the metal wires serves at least two purposes. Insulation prevents bare wires from touching and causing a short circuit and the different colors available aid in identification of the wire, which makes the job of wiring easier. For example, wire covered in black insulation can be used for the common (c) connections while green insulation can denote connections to the control (gapped) rail, etc.

Insulation must be removed from portions of the wire prior to installation. Wire strippers in various sizes are commercially available and are the easiest way to remove insulation. Another way to strip wire is by using wire cutters. Be careful to cut only the insulation and not through the wire itself. This method may take practice to perfect.

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