Wiring Large Layouts for Digital Command Control

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Summary: Wiring a large layout for DCC requires planning, but is not difficult.

This article deals with large permanent layouts, for other types of layouts refer to:
Main article: Wiring Your Layout

Analyze Your Needs

Before you can start on a large layout you need to spend a considerable amount of time planning it. At the end of the requirements phase you should know all of the following with a high degree of confidence:

  1. Your track plans
  2. Your baseboard construction plan
  3. Your projected locomotive roster
  4. The intended number of operators
  5. Your turnout types
  6. Your turnout remote operating system
  7. Your signaling system

All of these factor into how you will wire your layout.

Plan Your Wiring

At the end of the wiring plan phase, you will know:

  1. Number of power districts
  2. Booster and command station locations
  3. Sub-districts for occupancy detection
  4. Power bus wiring type and size
  5. Throttle network cable type and access locations
  6. Accessory bus wiring type and size
  7. Control panel locations
  8. Turnout status wiring strategy
  9. AC power wiring strategy, do you need additional outlets and/or overhead lighting?

Organize Your Approach

Once you have a wiring plan in place, you need to start organizing how you will approach this substantial undertaking:

  1. Plan to hire electrician to wire additional AC outlets and lighting
  2. Document how your wiring plan overlays your timberwork plan
  3. Pre-drill wiring holes in timberwork before or during construction
  4. Decide whether to wire before or after track laying
  5. Choose and document wiring color codes
  6. Acquire the necessary wiring tools, equipment and supplies
  7. Mount stationary DCC equipment in desired locations (or at least make placeholders) so you know where to bring wires to
  8. If you lack experience, practice soldering before you start wiring for real
  9. Label and document wires as they are installed

Test Your Wiring

In this phase you will ensure that all of your wiring is working correctly. We will break this down into two parts, before and after turning the power on! First, the dry-run tests without the boosters connected to the DCC power buses:

  1. Use a DMM or multimeter to check the resistance between each pair of bus wires, it should be "infinite" or in the megaohm range.
  2. Repeat this test for the accessory decoder buses.
  3. Check the resistance across each rail gap at the power district boundaries, again it should be very high. The power districts are supposed to be isolated from one another.

A simple trick is to use a continuity tester, be it a lamp, buzzer or a DMM with an audible alert. Connect the device across the two rails, and when it makes noise (or the lamp lights) you have a short somewhere. When the alarm stops, you have eliminated the problem.

After you have completed the dry-run tests you can start powering up individual boosters and testing them:

  1. Use a DMM, set to AC voltage, to test the voltage between the rails at various locations in the district.
  2. Test booster cuts out when the track is shorted (e.g., using the Quarter Test).
  3. Test voltage drop under full load.
  4. Test live frogs are working.
  5. Test rolling stock does not cause short circuits.
  6. Test rolling stock crossing between power districts.