Layout Wiring

Digital control systems drastically simplify the wiring of a layout, since many locomotives and accessories can all be operated directly from the digital voltage present in the track. This "plug and play" approach performs very well on small- to medium-size layouts and saves a great deal of time and effort during construction. Larger layouts however, demand significantly more power and organization, requiring them to be divided into several independent power circuits.

To get the most benefit from the digital power on your layout, digital accessory decoders should always be powered by a separate booster from digital train operations. This prevents a redundancy in the power allocated to accessories within multiple train circuits, and utilizes the power capacity of each digital circuit more effectively. Additional digital power can be conserved by operating lights and accessory motors from a separate AC power source, instead of from digital decoders or directly from the digital power present in the track.

Within each of these power circuits, a network of distribution points connects everything together. The distribution network is organized in a way that allows each circuit and each item to be isolated from the rest of the layout if necessary. The connections within a circuit must use suitable wiring for each application, and should always follow an established color-code for easy identification. All of the wiring and cables within the various circuits should be carefully routed and secured to prevent electrical interference with one another and to ease future modifications.

Choosing your layout's circuit divisions properly and following an organized wiring flow greatly improves the overall operation and safety of your layout, while making it easier to troubleshoot and facilitating its future expansion.

When planning the power circuit divisions of your layout, it is important to consider not only how much power, but also how power is used by each item on the layout. Locomotives and accessories use power in very different ways. While the power consumption of locomotives is relatively steady and continuous, accessories (turnouts, signals, relays, etc.) typically demand large impulses of power that place a significant strain on their power source. When several trains are operating in the same circuit and there is little power reserve remaining, the activation of turnouts and signals can become sluggish or may fail altogether.

The best solution to this problem is to create a "Digital Accessory" circuit that contains a dedicated booster and transformer to power all of your digital accessory decoders. This is possible since accessory commands can only be generated serially, one at a time, by the control system regardless of how many power circuits exist. By grouping your accessories into one circuit, it eliminates the need to allocate power within each digital circuit on the layout to reliably switch them. This allows the remaining circuits to power train operations exclusively, which results in a much more efficient usage of the power capacity of those boosters. The Digital Accessory circuit should be able to supply a minimum current of 1.5A to the accessory decoders, which can be provided by a smaller booster such as the Uhlenbrock Power 2 with its 2A output rating.

To further reduce digital power consumption, many accessories can be completely or partially powered by a standard 16VAC lighting/accessory transformer instead. These items include street lamps, turnout lanterns, signal lamps, and motorized accessories. Most modern turnouts and signals are equipped with separate lighting connections for this purpose, and older ones that do not can be easily modified. Connecting your accessories in this way relieves the internal power supply (the yellow output terminal) of the accessory decoders and the digital power circuit.

In summary, there are three major circuit divisions: Digital Accessory, Digital Track, and 16VAC Lighting. Within each of these major divisions, several individual circuit blocks may be required to supply the necessary power, for example: Digital Track1, Digital Track2, ..., Lighting1, Lighting2, etc. Each circuit block requires its own transformer, such as the high-output Märklin 60055 60VA model or the previous model 6001 (40VA). To achieve maximum capacity in the Digital Track booster circuits, the Uhlenbrock Power 3 3A booster is recommended along with the Märklin 60055 transformer. The following diagram illustrates these circuit divisions on a typical medium-to-large layout:

A well-organized wiring plan makes it easier to build your layout and to add to it in the future. The plan should include a way to electrically separate each circuit from the rest of the layout, as well as a way to easily isolate each item within a circuit. This can be done using individual send and return leads for each circuit along with a set of distribution points to connect the items within them. It also reduces wiring clutter and allows you to troubleshoot and resolve electrical problems more quickly and safely.

When connected to the control center with its own send and return pair, each circuit will form a "closed loop" that is electrically independent of all of the other circuits. In the event of a problem, any circuit can be easily isolated from the layout for troubleshooting. This also provides a clean low-resistance path for each circuit directly back to its own power supply. The return leads of each circuit are then commoned together directly at their power transformers. Important: If any of your equipment contains an internal "bridge" rectifier power supply, such as the Märklin Systems Central Station, Mobile Station, 60172 Booster or the Uhlenbrock Switch-Control, it is extremely important that their power transformers remain isolated from the common ground. To avoid permanent damage to this equipment, only their output return terminals may be connected to the common ground.

Within individual circuit blocks, a set of distribution points is used to connect to each item. The general distribution flow should follow a "fan-out" or branch approach, with a main distribution point located close to the power source (1-2ft) that connects several sub-points around the layout together. Each item on the layout then connects to the nearest sub-point. The distribution network can be made from commonly available screw-type terminal strips or the Märklin 72090 distribution strips along with their appropriate plugs (i.e. 71400). This allows for troubleshooting efforts to extend beyond the circuit-level, to specific items on the layout. A faulty item can be quickly disconnected from its circuit, tested, repaired, and reinstalled without cutting any wires.

The diagram below shows an example wiring plan using separate send and return pairs with a common ground, and a network of distribution points:

The type of wire that should be used in each application depends mainly on the distance and the amount of current that the wire will have to carry. This is due to the electrical resistance of the wire, which causes it to lose power as heat when current passes through it. As a general rule, greater distances and/or higher currents will require the use of heavier wire. It is also important that your wiring adheres to a basic color-coding system, which will enable you to quickly identify the general purpose of each wire.

Most items on your layout can be connected to nearby distribution points using 24- or 26-AWG wire, up to about 6 to 8 feet away. Low power signals, such as track occupation feedback, can use this thinner wire for longer distances if necessary. For connecting power to distribution points, 20-AWG or larger wire is recommended. The Märklin 71400 plugs and sockets will accommodate wire up to 16-AWG, appropriate screw-type terminal strips or other custom connectors must be used with heavier gauge wire.

Since many of the items on your layout will have wires pre-attached by Marklin, your color-coding system should follow theirs. The Marklin system is based on only 5 wire colors, to which you can add your own special-purpose colors if necessary.

Color	Name	Purpose
	"B"	Digital Voltage or Variable AC Voltage (0-17Vrms)
	"O"	Return / Ground
	"L"	Fixed Accessory Voltage (16VAC)
	Switched Ground	Activate Turnouts and Signals, Track Occupation Feedback
	Switched Power	Track or Accessory Power

There are some guidelines that should be followed when routing wires and equipment cables. Most important, every attempt should be made to keep the wiring of dissimilar circuits at least 1" apart to reduce electrical interference. In particular, the unshielded flat ribbon cables used with s88-style feedback modules, boosters, and the 6038 & 6039 interconnect cables are very susceptible to interference from the rapidly switching digital output signal of control units and boosters. To reduce potential interference caused by pure AC circuits, the send and return wires of each circuit may be twisted together, which will partially cancel the field generated around them. For all of these reasons, wiring should never be bundled together into conduits or channels.

To secure your wiring, small amounts of hot-glue every foot or two works very well. The hot-glue does not affect the wire insulation in any way, since the glue temperature is well below the melting point of the insulation. Unlike staples, the glue eliminates the risk of damage to the wire, and also does not generate any mechanical shock that can break delicate lamp filaments or disturb scenery material as is the case with hammering or staple guns. The glue is also easily removed if you need to change your wiring later. You can find a small low power hot-glue gun at most local hardware and craft stores.

When planning, building, and maintaining your layout, it is always important to keep safety in mind, both for your one sake as well as that of your trains and equipment.

Always use UL-, TUV-, or similar US or European safety commission, approved model railroad power transformers that are well-suited to the gauge of your layout and compatible with the power in your home. While it might seem inefficient to use five smaller 50VA HO gauge transformers instead of one large 250VA "industrial-strength" transformer, it is much safer in the event of a short-circuit. An over-rated transformer can melt wiring, track, and train wheels if a sustained electrical fault occurs. For these reasons, the power output of model railroad transformers is purposely limited by manufacturers based on their intended application (gauge Z, N, HO, O, 1, G, etc.).

When building your layout, always use the correct type of wire, connectors, and insulation. Thin wire and loose connections cause excessive power loss that can lead to poor or intermittent layout performance. Using wire of ample gauge and making clean, solid connections is the key to good wiring. Also, avoid unnecessary connections wherever possible by using long continuous sections of wire, instead of multiple shorter sections with splices. When splices are required, use suitable screw- or crimp-type connectors or directly solder and insulate the wiring with heat-shrink tubing or electrical tape.

Most importantly, always make sure that all power to your layout has been turned off before you work on or maintain your layout. If a failure occurs during operation, turn everything off as quickly as possible before attempting to resolve the problem. Most transformers, and some digital power units, will require that their power be cycled after an overload event to reset their thermal fuse and resume normal operation any way.

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