With DCC control systems so prevalent, the art of wiring a model railroad for multiple train operations with conventional DC power supplies isn't spoken about very often. DC block control remains a viable means of powering a layout, and you can always convert it to DCC in the future. Whether you are using DC or DCC, there are still applications where having separate track blocks can be an advantage.
Blocks refer to the process of dividing the railroad into sections, allowing you to control one train independently of another in a neighboring block. Real railroads also often divide their mainlines into blocks, designated by signals, to keep traffic at a safe distance and on the right track. On DCC systems, blocks are often used to operate signal systems and also to isolate problems.
How Many Trains Can I Run?
With DC controls, you will still be limited to running trains based on the number of power packs—or cabs—you provide. If you use rotary switches, you can add many more cabs later.
The number of blocks you need depends on your track plan. Generally, mainline blocks should be as long as the longest trains you run, or a little longer. Isolate passing sidings and places where you are likely to store trains like stations, staging yards, and engine facilities.
Avoid going overboard when adding blocks. The more you add, the more you have to manage.
Common Rail vs. Two-rail Wiring
When wiring blocks, you can either cut gaps in both rails or wire one rail constantly and only cut a single rail. This is called common rail wiring, which works well for wiring signals with most blocks. With reverse loops, you will have to cut both rails. You can use various types of model train switches for this project.
Model trains get their power from the rails, so to isolate the trains with DC control, you need to isolate the tracks. You need a small break in the rails to accomplish this. You can cut one rail -- called common rail wiring -- or both. Locate the gaps carefully.
An easy way to cut gaps anywhere you'd like on the layout is to use a cut-off disk in a motor tool. This way you can lay all of your track and add blocks later. Wear eye protection when using this tool. Alternatively, use insulated joiners to separate tracks. These plastic rail joiners will help keep rails in line without carrying current. A plastic joiner is not necessary to block the current -- a gap alone is sufficient.
Hooking up the Wires
With the blocks cut, it's time to hook up the wires. For two-rail blocks, run at least one pair of wires from each track block to the center poles on a DPDT toggle switch or rotary switch if you are using more than two cabs.
Bus wires connecting all of the upper and lower poles of the DPDT switches will distribute power from the two cabs. To control the power by cab A, turn the toggle switch up. For cab B, turn the switch down. If you use a DPDT-center off switch, the block can also be turned off completely so neither cab has control.
You'll need at least one pair of wires (one for each rail) per block. For shorter blocks, a single pair may do. For longer blocks, multiple feeders attached to a common bus will provide better current. You may also want to use this combination of smaller gauge feeders and heavier bus wires on the short blocks too if you have a long run between the track and the toggle switch. It is much easier to attach the smaller gauge wire to the rails themselves, but the light wire may not be able to deliver adequate voltage over a run longer than a foot or two.
Toggle or rotary switches can be located on a central panel, or along the fascia of the layout. The latter will allow you to walk along with your train if you have a walk around throttle control. This option will also shorten the wiring runs from the track to the cab busses. On smaller layouts, a centralized panel is often an easier option. Panels can also be used on larger layouts where a dedicated operator or dispatcher aligns the power for the different engineers.
Either way, the wiring on the back of the switches is the same. Choose switches that are rated for the voltage and amperage of the trains you are using. Some switches use screw terminals, others have tabs for soldering wire connections or using crimp connectors. Any will work.
Attach the two block wires from the track to the center poles on the back of the switch. Keep the wires consistent throughout all of the blocks. Do not cross wires. Color coding the wiring will help.
Run a pair of wires from the first power supply -- cab A -- to the lower pair of poles on the switch. Run a second pair from another power supply -- cab B -- to the upper pair of poles. The physical position of the toggle switch will be opposite of the "live" wire connection, So lifting the switch up will connect the track wires to the lower bus, cab A.
As with the block wires, use a heavy enough wire gauge for these cab busses. No. 14 or No. 12 should work for most applications. Color coding the different busses is also a good idea. Note the color codes for all of your wiring. Label the toggle switches with the block name/number and the cab assignments. Do this on the panel for operators and on the back at the switch for maintenance.
Here are a few links to some additional track-wiring applications you may encounter:
- Reverse Loops: These track sections that turn a locomotive or train, such as a loop, wye or turntable, require special wiring to avoid a short. This is easy to do for both DC and DCC.
- Signals: This basic directional signal adds a little operational flavor to a basic DC block system.
- Block Detection: For more elaborate signaling systems, or to track trains in hidden areas, you can add block detection to your block wiring.