On30 Modules Mid Atlantic Division

Standard Version 2.01

Revised May 16, 2010

Contents Page

Introduction 2 1. Module Construction 3 2. Track 5 3. Control and Wiring 8 4. Scenery 9 5. Definitions 10 6. Websites 11 7. Revision History 12 8. DCC Universal Bus Construction 13

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Introduction The Mid Atlantic On30 module standard is based in part on the simple Free-Mo Standard posted at www.Free-mo.org. In addition, various parts of this standard evolved over time through the various conversations (and heated arguments) on the On30 Modules Yahoo group. The primary purpose is to provide a set of guidelines that would allow members to independently construct modules that could be joined together at shows and give the appearance of having been built as a sectional layout. The NBR&N (modular) and the Yosemite Short Line (sectional) are two groups that have provided a great deal on inspiration for this work. The modular assembly has been conceived of as a point to point railroad for greater operational possibilities. Continuous running, as such, is not integral to the design of any module. Return loops, Wyes and Turntables will be employed to turn trains. Free Mo does not specify the actual methods of module construction. This is left up to the individual builder. Only the module ends, track placement, track connection, module height, electrical requirements and basic scenery suggestions for uniformity are specified. David Michailof assembled the original standard. The standard borrows from many sources from the web, and this document could not have been created without using (plagiarizing) their information. Their website locations are included under the website listings. In addition, the majority of the DCC Electrical Standards were developed by Geren W. Mortensen Jr., (the Universal DCC Bus especially!) and Chris Abbott. Without their work this document would not be possible. The group experience of five years, and the designs and discoveries of Kevin Hunter and Berrett Hill Trains has contributed to the development of Version 1.2.0 and the inclusion of the Acceptable Variations in an attempt to create a more inclusive standard. The Basic Standard establishes the rules that apply to all modules. The Advanced Standard can be used to increase creativity and covers mainline grades and free form design. Recommended Practices should be employed for greater continuity, but are not mandatory. The Acceptable Variations allow more opportunities for innovative module design. The 2010 Revision These revisions are primarily intended to allow greater flexibility and ingenuity amongst our modelers, and to let more modelers get together and have more fun. Included are some basic guidelines for implementing these variations without strife. Stars ★ indicate minor updates to the Basic Standard. The Acceptable Variations were added in May 2010. These are a series of useful exceptions intended to allow a broader interpretation of the original standard. Under the Acceptable Variations almost any innovative modular concept or well-constructed module from any other standard can also be allowed to operate under the Mid-Atlantic standard. The only provision of implementing any acceptable variation is that resolving any difficulties caused by integrating a variant module in a setup is the responsibility of that modules owner. Under the basic standard Module builders are free to build modules, 2’ wide by whatever length is desired. Under the advanced standard and advanced variations, module dimensions and shape are left to the imagination and artistic license of the module builder. The original standard has shown over time to have the unfortunate side effect that designs for curves and certain other module layouts require larger bulkier modules than really required. In recognition of these limitations, variations in plate dimensions and off-center track placement are now allowed. (Hats off to the Texas Outlaws) The Basic standards assure universal compatibility.

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1. Module Construction 1.1 Basic (Mandatory) Standards 1.1.1 Interface Plates are to be 6 inches high by 24 inches wide (See Note on width) by 3/4” thick plywood (birch plywood works well). To allow room for C-clamps, keep the inner surface of endplate clear of obstructions (electrical terminal blocks, Loconet connectors, etc.). Recommended clearance area is 2” high by 4” wide, centered at bottom edge of endplate inner surface. Note on width: 24” is intended as the overall module width. If your fascia extends across the end plate, be sure to narrow the width of the plate accordingly.

Figure 1.1.1: Module End Plate

Alternate end plate widths and heights are covered under Variations 1.4.1 & 1.4.2

1.1.2 Module Length is left up to the discretion of the builder.

1.1.3 Module Frame and Surface should be constructed of dimensionally stable materials to ensure proper alignment with other modules under all possible environmental conditions. Avoid dimensional pine lumber. It has a tendency to warp and ‘cup’ throwing off track alignment. In its place, consider using materials such as plywood ripped into strips the equivalent size of dimensional lumber, other types of laminates, extruded foam sheets, etc See website listings for module construction suggestions.

1.1.4 Default Height to the Railhead from the floor is 50 inches. Each leg must include vertical adjustment of +/- 1 inch minimum to compensate for uneven floors. This should provide an adjustable rail top height from the floor between 49” and 51”. See website listings for leg suggestions. 50” is the standard height for the NBR&N. 48” is the standard for many other groups - members may wish to consider making legs adjustable from 47-51” This can easily be done with 4” cabinet levelers from Lee Valley tools.

1.1.5 Sub-Roadbed shall be constructed to prevent sag or flexing. 1/2 inch plywood, well braced ¼” plywood, thick or braced foam, and plywood/homasote combinations are all acceptable.

Each module shall be equipped with sufficient legs to be Freestanding and a module must stand secure and level, independent of other modules, through the use of proper cross and angle bracing. Modules must have finished fascias on each side because they may be used with spectators viewing from either side, or both sides at once.

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1.2 Advanced Standards 1.2.1 Module width between end plates is left to the discretion of the modeler. Consider 12 inches as the minimum width to allow sufficient scenery between the track and module edge to protect equipment during a derailment. Module end plates between permanently mated modules (module sets or sections) can be of a different width. Only the end plates designed to be interchangeable with other modules must meet the 24” standard.

1.2.2 Mainline Grades: Mainline grades are allowed on modules.

♦ Module grades must not exceed 4% (1” every 24”) on mainline trackage. ♦ Track must be level for the 6” prior to each interface. ♦ Suitable Easements are required between grade and level track. A recommended

minimum would be an 8” transition from level ground to a 4% grade. This imposes a practical limit of a <2” rise over a 4’ module, and a <3” rise over a six foot module (6” level on each end, 8” transition to grade (2 1/4 ft) + 1” rise per each additional foot of module length.

♦ Opposing Interfaces may be of different heights.

1.2.3 Module Legs must be adjustable from 40-60”. There are several plans for different types of legs in use. See website listings for leg suggestions.

1.3 Recommended Practices 1.3.1 Module Skirts can be used. Both sides of a module can be skirted. The ends of the skirts will extend two inches past the module end plate to allow overlap from the skirting on an adjacent module. The bottom edge of the skirt should be 1” off floor when the leg adjustments are set to the modules minimum height.

1.4 Acceptable Variations 1.4.1 Module Interface Plate widths other than 24” are acceptable.

30" width and 12" module end plates already exist. 8" width is a practical minimum.

1.4.2 Interface Plate heights other than 6” are acceptable. 4" is recommended as a minimum. Note: Appropriate clamping or attachment of modules varying from 6" height shall be the responsibility of the owner of the variant module.

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2. Track

2.1 Basic (Mandatory) Standards 2.1.1 Mainline Track Height shall be code 100 nickel-silver at each interface. Flex track or hand laid track is acceptable.

Alternate track height is discussed under Variations 2.4.1

2.1.2 Mainline Minimum Radius is 26 inches (32 inches is preferred) with at least 12 inches of straight track between reverse curves on mainline modules.

2.1.3 Track Shall Be Centered at the module ends (see fig. 1.1.1). Alternate track locations are allowed under Variations 2.4.2

2.1.4 Track Must Be Perpendicular to the endplate.

2.1.5 Track Must Be Straight and Level for 6 inches from each end of the module (see Fig 2.1). By ensuring 6” of straight track from each module, the 12” between reverse curves can be maintained. Note this track placement makes the ends of the module interchangeable.

Eliminating the 6” straight requirement is discussed under Variations 2.4.3

2.1.6 Setbacks and Fitter Rails: Rail shall be cut off 1 inch away from module end; ties and ballast shall be continued to the module end for good appearance and matching with the adjacent module. Appropriate lengths of rail should be carried with each module to provide the short fitter rails used to bridge the 2 inch gap across joined modules endplates.

Alternate rail terminations are discussed in Variations 2.3.5

Figure 2.1.6 – Fitter rail

2.1.7 Ties will be commercially available low profile ties or home made equivalent. Track with ties in the dirt (no roadbed profile), will be used at the interfaces. (see fig. 1.1.1)

Alternate tie placements are discussed in Variations 2.3.6

2.1.8 Mainline Turnouts where the main track travels through the curved portion of the turnout shall be ★ #5 or greater. A turnout in the mainline where the main track travels through the straight portion of the turnout may have a sharper curve, with a lower frog number. All frogs will be powered. This has proven very important for smooth operation.

2.1.9 Mainline Track will be placed no closer than 6” from the track centerline to the side edge of a module. Yard or industrial spur tracks will be placed no closer than 4” from the track centerline to the side edge of a module.

Placement of track within 4” of an edge is discussed in Variations 2.3.7

2.1.10 Easements will be used when making the transition between straight and curved tracks.

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Note: An easement is recommended at each end of all curves. Experience with many available models show that longer cars and engines have difficulty entering a 26” curve from a straight tangent track. Easements and vertical curves are a courtesy that will allow many more visiting trains navigate your module. See en.wikipedia.org/wiki/Track_transition_curve.

2.1.11 ★ Vertical curves will begin and end each grade.

2.1.12 NMRA On3 Clearances should be used for all track.

2.2 Advanced Standards 2.2.1 Mainline Track can be code 83 within the module, but must provide a transition to code 100 at the interface. Code 55 may be used on sidings if desired.

2.4 Acceptable Variations 2.4.1 Rail height may vary. The owner of the module with the variation from code 100 rail must ensure the accommodation of different sized rail. 2.4.2 Track may be placed off center. See 2.3.5 for a discussion of how far off center. Basic Standard Wide Module Texas Outlaw Layout Berrett Hill

Figure 2.4.2 :: Examples of various track placements:

Module builders placing tracks off center must carefully consider section 4.1.3 2.4.3 Track Must (still) Be Perpendicular at the endplate and Level at each end of the module. This rule will not change. ever.

Note that endplates are not required to be perpendicular to the rest of the module, and if an angled exit is desired the endplate may be constructed at an angle to the length of the module.

Figure 2.4.3 :: Examples of angled track exits:

2.4.4 Curves within the last 6" of a module are allowed. Note that this practice is generally not recommended. It should be understood that such a module might be excluded from universally mating with certain other modules, due to the creation of dreaded reverse curves. The stigma of a deformity, like a curve near the end, in any given module must be announced whenever plans are being drawn up for a joint display. The responsibility for proper planning and placement of such a module shall fall upon the modules owner, and shall be subject to whining and disgruntlement.

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In planning a "curves to the end" module, like any curved module, a spiral easement (en.wikipedia.org/wiki/Track_transition_curve) is suggested. A spiral curve will reduce the amount of curvature at the end plate, and better accommodate an attached straight track module. Note that the Berrett Hill Standard consistently runs curves to the endplate, but accommodates this problematic situation with the concept that each end is left or right handed. Examination of this arrangement shows that not every module can mate with every other; left mates with right, and right mates with left. The difference is made obvious under the Berrett Hill Standard in that each track is also 2" left or right of the modules centerline.

2.4.5 Rail Setback: Rails built flush to the endplate are now allowed. Modules without setbacks may be attached so that trains travel over an open gap as an alternative to the suggested fitter rails. Any module owner that varies from the 1" rail setback must make arrangements to link to modules using the original standard. Methods of compliance include:

a. Leaving about 1/4" of rail extending at the end to clip on a joiner. This will mate using only a 1" fitter rail and some joiners.

b. Use of adapter modules with 1" setbacks on one end. c. Any other clever method of connecting to other modules with 1" rail setbacks.

It should be noted that flush rail ends are not a recommended practice, and though good results have been achieved, great frustration awaits the unwary. Those who have only one or even several modules may find that carrying a few bits of rail and joiners is far more simple than planning to deal with expansion issues and alignment concerns. This method has been shown to work very well within a sectional group. See Geren Mortensen for advice on this point.

A discussion of this method appears at www.berretthill.com . 2.4.6 Ties: Ties on raised roadbed are allowed as an alternate to track "in the dirt" construction. (N scale cork slightly elevates the track, and allows tie ends to float out of the ballast). This construction may cause an unsightly scenery gap as different height modules mate. It is therefore the responsibility of anyone with raised roadbed to carry a pocket full of scenic grass, lichen, or scenery fluff to mask, hide, or otherwise accommodate an uneven joint between modules.

Following this line of thought, since there is no scenic color standard for the MADModules it would be really clever to carry some loose scenic material that matches your module. In this way a light sprinkling across the joint will blend two different scenic colors or textures and improve the total show appearance.

(Berrett Hill Modules use Scenic Express "Adirondack Blend" near all endplates). 2.4.7 Track Placement: Tracks may be placed as close as 4" to an edge. Placement less than 6" from an edge should be planned with some "scenic restraints" such as bushes, fences, telephone poles, or elevated terrain to prevent unwarranted experiments testing the gravitational constant. (Trains on floor are much less fun than trains on tracks.) Any locomotive or rolling stock owner may ask owners of modules with insufficient protection of rolling stock:

a. to temporarily add such protection for a show b. to install their module in a non mainline or end of track location, so that running on hazardous

trackage may be easily avoided by any locomotive or piece of rolling stock. c. to be excluded from a show if no other option is workable

--This is a good area for the daring to think carefully, and consider a "good neighbor" policy...

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3. Control and Wiring DCC has been chosen as the standard for the Mid Atlantic Module group. The nearly limitless possibilities for multiple cabs combined with the option of onboard sound made this an overwhelming favorite. The universal DCC throttle bus designed by Geren W. Mortensen Jr. will work with NCE, Digitrax, Lenz DCC and certain other DCC systems utilizing a 4 or 6-wire bus architecture. See DCC Universal Bus Construction and Components.

3.1 Basic (Mandatory) Standards 3.1.1 Terminal Blocks 10 Amp Barrier Style shall be installed at each interface and shall accept #12 AWG wire with soldered spade tongue lugs. ★ EuroStyle terminal blocks with direct wire connections are also acceptable. Larger sized blocks with ratings of 35 amps or greater are recommended for their larger wire. 3.1.2 Two Conductor Wire Bus Of #12 Stranded shall extend full module length under mainline. 3.1.3 #18 AWG Feeders will connect individual rail lengths to the rail bus

Alternate use of #20 wire is discussed in Variations 3.4.2.

3.1.4 Inter-module Connector Wires shall be #12 AWG, 10" long with soldered spade lugs. Additional use of PowerPole connectors is discussed in Variations 3.4.3.

3.1.5 Accessories, except DCC controlled turnouts, shall not derive power from track power 3.1.6 A DCC Data Bus Cable, Male-Male, the length of each module plus 18” will accompany each module. At the minimum, one F-F Coupler shall be carried for interconnection with other modules. DCC cables shall be constructed in accordance with datasheet “DCC Universal Bus Constructions and Components”

3.4 Acceptable Variations 3.4.1 #20 AWG Feeders may be used when each rail section is powered separately. 3.4.2 Inter-module Connector Wires may include Anderson Powerpole connectors for quick connection. Many modular owners appreciate their speed and ease of setup and breakdown. For universal proper connections when using Andersen Powerpoles the Red connector should be connected to the Right hand rail as seen facing the end plate. This means that red will connect to different rails at opposite ends of each module, and connectors must always be connected red to black, and black to red.

It is recommended to carry additional pigtails or spare wire for quick attachment to other modules not equipped with Powerpole connectors. See the Berrett Hill Website for details

Figure 2.4.3 :: Anderson PowerPoles installed.

Note that colors will be cross-wired on one module end as shown here.

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4. Scenery 4.1 Basic (Mandatory) Standards 4.1.1 A Flat Scenic Profile should be used at the module standard end(s). A module should not only have universal ends in a physical and electrical sense, but also in a scenic sense as well. Having a scenic element that abruptly ends at one module end, like a mountain, river, or road, detract from the ‘one layout’ scenic ideal.

At an internal interface between two sections of one multi-section module, these requirements do not apply.

4.1.2 ★ No Official Fascia Color is suggested, since 4 out of 5 modules built so far are not painted with the color blessed in the original standard. The original specified module fascia color Glidden Evermore "Stoney Creek" paint is no longer available. Dark or muted colors are preferred. Avoid garish tints. Please no fluorescent colors.

Geren Mortensen has commented: “I personally think that the fascia color and skirting should be tartan plaid. Please take the time to research and procure the correct colors and pattern for your clan.”

4.1.3 ★ Module owners must take responsibility for general appearance. When building to any Acceptable Variation in this standard, owners must cover, paint, camouflage, or otherwise "make pretty" any jutting endplates or exposed unfinished module parts caused by their innovative designs. Failure to comply may provoke snide comments, name calling, and similar derision from your fellow moduleers.

4.3 Recommended Practices 4.3.1 Hand Throws are encouraged where practical to actuate turnouts.

It is strongly recommended that turnout actuators, whether manual or powered, be installed in such a way that each may be operated locally, and from either side of the module.

4.3.2 Standard Ballast Techniques are encouraged. A mix of (2) parts grey number 75 to one part cinder number 76 is preferred. These are Woodland Scenics products and the fine grade should be used.

4.3.3 Ground Foam Grass and Soil in the ballast is recommended as an occasional scenic event - especially on less used trackage.

4.3.4 Rails may be painted rail brown with occasional rust streaks.

4.4 Acceptable Variations 4.4.1 Additional variations in appearance or construction that do not cause injury, threat to property, or broad gross embarrassment will be acceptable. The test for such embarrassment shall be the statement by any compliant module owner that "I can't connect to THAT!” Such a statement, if held to, after persuasive argument and negotiated accommodation, may not be contested and will hold for the duration of that show. Modules considered unacceptable may be excluded from operation, and in extreme conditions made to hide under a sheet or equivalent.

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Definitions These definitions are provided to establish a common basis of understanding of the following standards.

Accessory Power Bus: The continuous two wire bus powering electrical accessories such as turnout motors, structure lighting, animation, etc. DC: Direct Control through convention throttle/power pack. DCC: Digital command control DCC Control Bus DCC Control Panel Endplate: The specified end surface of a module that joins with an adjacent module. Fitter rails: The 2” long removable rails and joiners used to bridge the joints between adjacent modules or sections. LocoNet Bus: The continuous six-wire bus carrying DCC information among the DigiTrax brand DCC system components such as throttles, boosters, radio receivers, etc. Mainline Track: On every module there is at least one route that connects the middle of the first interface with the middle of the second interface. One of these routes should be designated as the mainline route and must obey mainline track restrictions- all the other trackage does not. Module: A section of a portable layout that has a common endplate, track connections and electrical connections to mate to other units and features a single track mainline. Portable layout is constructed to provide a point-to-point, point to loop or loop-to-loop meandering main line. A module may consist of multiple subsections. Module (Basic): Unit of a portable layout that is level and of a fixed dimension, typically 2X4, 6 or 8, Module (Advanced): Unit of a portable layout that may feature grades. Dimensions are not fixed and allow for a unit of any interior width, length or geometric shape. Pigtail: Connector/wire assemblies used to connect any of the electrical busses together between modules. Passing Siding: Parallel track that allows one train to overtake and pass a second train. Length is sufficient to hold entire train. Located along single-track main lines to facilitate passing. Run-around Siding: Parallel track that allows motive power to run-around a cut of cars to switch a facing point spur. Length is not sufficient to hold an entire train. Located in industrial areas to facilitate switching operations. Single Track: Single track that allows continuous operation of trains in one direction. Combined with multiple passing sidings, intermittent operation of trains in opposing directions is possible. Section: A part of a larger Module. Used in conjunction with other sections and assembled in the same configuration to create that module. Conforms to end profile, track and electrical connections only on the ends that mate with other independent modules. Typical examples include a long yard, passing siding or turn back loop constructed of multiple sections that only mate together in one configuration. Standard end: A location where a module will connect to other modules; also contains an external interface that must meet all mandatory standards. Track (Power) Bus: two wire bus feeding power to the track,

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Websites Free-Mo resources Free- Mo Yahoo group Free-Mo resource site by Chris Palomarez

Guidelines to different groups Free-Mo standards

Slaughter guide Northern Cal guidelines Calgary Free-mo module specs

Module designs

Free-Mo site Free-Mo 1Design/Construction More Module Plans 45 degrees Module Set-up Benefits 45 degrees Free-Mo Bench work Track termination plate Mini-mo & double sided Easement Design on Shandin loop N California San Luis Obispo Central Arizona Bob Schrempp's loop

Leg construction

Troughton Not another module article folding ABS legs (scroll down for legs) Free-Mo site article on folding legs 1x2 using LeeValley leg brackets by the Arizona RR Society Free-Mo site article on ABS legs by Robert Moore Northern Cal leg design 2x2 using Lee Valley leg brackets Calgary Free-Mo using 2x2 leg pockets (Scroll down)

Track work

creating easements for curves mounting of recessed switches easy flush mounted switches

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Revision History Version 1.1.00 Revised September 6, 2005

Announced Imminent Update February 2, 2009

Version 1.2.00 Revised May 16, 2010

Added the Acceptable Variations sections Changed turnout requirement from #6 to #5 since almost all pre-manufactured turnouts are #5. Clarified mainline turnout wording.

Clarified curve easement wording.

Eliminated requirement that all spur tracks be electrically isolated.

Updated Facia Color.

Added "Responsibility for Appearance" clause.

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DCC Universal Bus Construction and Components The Components in Figure 2 are used to construct a Cab, XpressNet or Loconet throttle network for standard modules. If followed, these wiring diagrams will allow creation of a DCC throttle network that is completely compatible with the most popular DCC systems - The universal DCC throttle bus designed by Geren W. Mortensen Jr. will work with NCE, Digitrax, Lenz DCC and certain other DCC systems utilizing a 6-wire bus architecture. This specification calls for readily available, inexpensive parts. While callouts are indicated for Tony’s Train Exchange part numbers, an equivalent part from another source may be substituted, as long as it meets the same specifications as the listed part. Each Module shall carry at the minimum a single Pass-thru cable equal to the length of the module plus 18” (to allow for interconnection) and one F-F coupler. These can be obtained through the group. It should be noted that the wiring for each cable is identical - a relationship of Pin1-to-Pin1 is maintained throughout the bus. This allows any cable to be substituted for any other cable as needed. This same cable is also used for the throttle cables on NCE/SystemOne Cab Bus- and Lenz ExpressNet-based systems. Digitrax throttles use this connector as a default. The following wiring diagram, Figure 1, illustrates the basic cable used in all instances. It is a simple 6-wire data cable using 6P6C RJ11 connectors and 6-conductor flat telco/network cable. These cables can be ordered custom made to any length, or may be made by the modeler with relative ease. The cable is inexpensive, at approximately 12 cents per foot, and the connectors can be obtained for approximately 30 cents each (or less, in quantities). This cable, along with a Female-to-Female coupler fulfills the minimum DCC “pass-thru” requirement for a module.

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Throttle Bus Components

Six conductor Flat Phone Cable - Tony’s Train Exchange P/N M6C or equivalent RJ11/12 six position Plugs - Tony’s Train Exchange P/N M PG or equivalent Female-to-Female Coupler - Tony’s Train Exchange P/N M FF or equivalent Two way Splitter Tony’s Train Exchange P/N M SP2 or equivalent (1 RJ11 Plug-to-2 RJ11 Jack) Universal Throttle Connector Panel – Tony’s Train Exchange P/N UTP/TTX or equivalent 12V DC 1 amp filtered power supply – Tony’s Train Exchange P/N TTX-XNCE or equivalent

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The next diagram illustrates the connection of a throttle connection point onto the DCC bus. The connection point, referred to as a Universal Throttle Panel (UTP) can be inserted anywhere on the layout it is needed. It is simply connected between two Pass-thru Throttle Bus cables. Some modelers may wish to include a UTP permanently on their module, especially if their module provides a point where operators may wish to stop to operate trains (e.g. A switching module or yard). Alternately, these may be placed between modules as needed in place of a Female-to-Female coupler to provide additional plug-in capability. The UTP is truly universal, and is compatible with throttles from the previously mentioned manufacturers. In some cases, the manufacturer’s cable has been replaced with a Pass-thru-type cable.

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On large layouts using NCE or SystemOne DCC systems, it is necessary to “inject” power to operate the throttles at intervals around the layout. This is due in part to the power supply voltage drop over long runs of small-gauge wire typically found in telephone network cable. For NCE and SystemOne DCC systems, this distance is between 30 and 40 feet. The specified power supply is of the “wall wart” variety, and simply plugs into the small jack on the rear of the UTP. It is important to observe the “direction” of data flow when inserting the power supply to avoid feeding the 12VDC back into the command station. The UTP circuit board is marked to indicate which connector should be fed from the command station. When properly installed, the UTP, the UTP will open the appropriate circuit to prevent 12V from feeding back to the command station. This additional power supply is not necessary when using a Digitrax or Lenz DCC system.

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In situations where there are branching modules, the DCC bus should branch as well. This illustrates how a two-way splitter plug can be used to accomplish this branching. Notice that power insertion is indicated on the branch. This may or may not be necessary, depending on system type and the length of the branch. It is theoretically possible to branch as often as desired, up to the cumulative limits of the total system bus length. The maximum bus length for Digitrax Loconet and NCE/SystemOne Cab Bus is approximately 1,000 feet. Systems using eXpressNet may reach up to 3000 feet. In all cases, the DCC Throttle Bus must NEVER form a closed loop. While there is little chance of component damage, operational problems may occur if a loop is formed.