Practical considerations and quick tips
For those who have a medium to large size layout, and wish to use a tested recommendation for new wiring, I offer the following:
1. The power bus and control bus need to be physically separate under the layout (recommend 12-18 inches or more if possible). When they need to cross, try to do so at right angles. Keep both away from any household AC (110VAC) wiring as well.
2. Use “Ethernet” network cable (termed “CAT3” or “CAT5” – Category 3 or Category 5) for the control bus runs instead of the flat “modular” phone cable. This has built-in twists that shields from interference.
3. Make power bus runs with 12AWG stranded wire. This is available from Home Depot, in a variety of insulation colors, as 500 foot spools that they label as “12AWG 19/W Type THHN or THWN.” Stranded wire bends, and pulls through holes, easier than solid. It is also harder to damage than solid wire. For those concerned about the “AC surface effect,” stranded wire has more surface area (because it is made up of multiple individual wires) than the same size solid wire. If you have an extra-large layout, you may want to use 10AWG stranded wire. You may want to loosely twist the power bus wires together (a twist every 1-2 feet).
4. Make feeder drops from the track as short as possible, 6-10 inches is a good standard. Use 22AWG or 20AWG solid pre-tinned wire. Solid wire, and especially pre-tinned solid wire, is easiest to solder to rail. As long as the length is kept this short, it will not cause a significant voltage drop. Use rosin-core solder to make the joints. 22AWG solid pre-tinned hookup wire is available in 100 foot spools, in a variety of insulation colors, from Wire Works, Box 443, Guilford CT 06437. Local electronics or hobby shops may carry it (Gateway Electronics in St. Louis does).
5. Connect a feeder to every piece of rail. If that seems like too much work, connect a feeder at least every 5-6 feet with code 83 or 100 rail, or every 3-4 feet with code 55 or 70 rail.
6. The most reliable connection between the power bus and feeder drops would be to solder them together. I have done a number of railroads this way, and recommend against it as there is a much (much) faster, safer (no more burned fingers or legs), and almost as reliable method available. This is by using “3M Scotchlok self-stripping electrical tap connectors.” These are available from electrical supply stores for $.19-$.24 each in boxes of 100.
Connect the 12AWG stranded power bus (run) to the rail feeder drops (tap) using the 3M Scotchlock 567 connector (p/n 054007-14887). This connector is specifically designed to connect a bus run (12 or 10AWG solid or stranded) to a feeder tap (18-14 AWG solid or stranded). I, and a number of my modeling friends, have had good success connecting a 12AWG stranded bus to the Wire Works 22AWG solid pre-tinned feeder with these connectors (your success may vary by the brand of 20-22AWG wire you use), but it’s not a guaranteed connection. A better approach would be to solder a short length of 18 AWG solid wire to the Wire Works 22AWG feeder before installing it on the layout – then you are using 18AWG wire in the Scotchlock connector. No stripping at the Scotchlock is necessary, the connector clips over the power bus wire, and the feeder slides into a hole. Crimping with a pair of heavy pliers makes the connection. A special crimp tool is available that make this even easier and quicker. Closing the connector cover insulates the connection.
If you need to connect two 12AWG bus wires together, use the 3M Scotchlok 562 (p/n 054007-11032). It is designed to connect two power runs, either 12AWG solid or stranded or 10AWG stranded only. Note that significantly more pressure is required to crimp this connector correctly.