Modules: S-MOD

The NASG S-MOD Standards were developed and approved in July 1987. This standard allows S-scale modelers to gather from anywhere and easily join their modules into functioning, hassle-free layouts. These standards have been accepted by the NMRA Engineering Committee as the basis for the NMRA's S-scale module standards. They accommodate standard-gauge, narrow-gauge, and/or hi-rail. Track and wheel dimensional standards match those described on our dedicated Standards page.

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Official Documentation

The first document describes the physical construction requirements for a module to meet the NASG's S-MOD standard. Note that this standard's requirements are kept to an absolute minimum, so as to allow for maximum flexibility and freedom of implementation, yet still allow for random modules' integration into functional layouts. This standard allows for closed-loop as well as point-to-point layouts, or a combination of both.

NASG S-MOD Physical Module Standards (PDF).

After the physical construction, the next most important aspect of getting modules to work together is the electrical sub-system. The document below describes the accepted recommended practice for creating the electrical sub-system for S-MOD modules.

Important: the electrical design was created in the late 1980s. At that time Digital Command Control (DCC) wasn't as common as it is now. The NASG BOT is currently (2020) working on a revised design that will allow for DCC. Also note that the interconnecting plugs referenced in the document below, the famous Cinch plugs, are no longer available, and neither is the company through which everyone bought these plugs, Radio Shack.

NASG S-MOD Layout Electrical System (PDF).

Below is a follow-up article written by Don DeWitt describing how to check and verify the wiring of your module.

NASG S-MOD Layout Electrical System (PDF).

NMRA Reference Documents

As a source reference, the following NMRA documents cover the standards for modules in all scales, including S.

Probably the largest gathering of S-MOD modules ever, the 1990 NASG Convention in Pittsburgh, PA (click for large version)
(see August 1990 NASG Dispatch)

Example Implementation

The key drivers behind the S-MOD standard, Don Thompson and Don DeWitt, wrote a four-part article for the S Gauge Herald magazine on how to construct S-MOD modules following the above-referenced standard. These have been made separately available below. The first article covers various designs that are possible with the S-MOD system.

  1. Planning the Module (PDF)
  2. Building the Benchwork (PDF)
  3. Laying the Track (PDF)
  4. Installing the Electrical System (PDF)
The over 30 modules of the Houston S Gaugers at 2014 World's Greatest Hobby show in Houston, TX (click for large version)
(copyright © Peter Vanvliet; used by permission)



Houston S Gaugers

The Houston S Gaugers' club founder, the late Jack Troxell, built a set of three modules that make up a double-track wye. He did the benchwork and the track work. Club member Peter Vanvliet took over the set of modules several years later to complete the electrical work, the ballasting, and the scenery. The "Henderson Tower" controlling the traffic through the wye is a kit donated to the club by former club member Tom Henderson. The kit was manufactured by American Model Builders and built by Peter Vanvliet. The structure in the foreground was built by Ria Vanvliet, of a kit manufactured by River Dam Model Works. The trees were scratchbuilt by Peter.

(copyright © Peter Vanvliet; used by permission)

The photo below is a close-up of Jack's fantastic track work. The Houston S Gaugers' club layout's track standard is code 100 rail. There are a total of 6 crossing frogs on the entire set of modules. To make the electronics work with DCC, the club has a dedicated Digitrax Booster to run the wye and the third leg coming off of the wye. It uses one Tam Valley Depot "Hex Frog Juicer", which has 6 outputs. To control the six turnouts on the module set, the club uses the Fast Tracks "Bullfrog Manual Turnout Control", which includes a built-in switch to control the polarity of the turnout's frog.

(copyright © Peter Vanvliet; used by permission)

North Penn S Gaugers

This is the scene of a module on the North Penn S Gaugers club layout.

(copyright © Hugh Sinn; used by permission)

We would love to show one or two photos of your club's layout here. Contact the webmaster (see at the top of this page).

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