The main bus feeder wires for DCC distribution should be run close together rather than two widely separated wires. Many will argue about the size of the wire and/or evidence that it works OK some other way. Best practice:
1. Select a wire size to reduce the overall voltage drop at rated booster current. This usually means 12-14 AWG. Obviously Scale and layout size dependent.
2. Use twisted pair with 3-4 twists per foot. This reduces the effects of wiring inductance and radiated electrical interference to other circuits. It also requires them to be close together where 16 AWG 'zip cord' or speaker wire automatically does that. Fancy labeled speaker wire might be available in a larger gauge but will cost more that 12 AWG building wire.
3. Add an R-C snubber/filter at the far end of each bus run away from the booster.
4. Position the booster near the middle with bus runs out in 2 or more opposite directions rather than at one end. This minimizes the booster to load distance of the wiring.
I have just strung a 14 gauge DCC buss under the layout. The two wires are separated by about 6 inches at the closest. Do I need to re string the wires with a twist periodically? How close together should the twists be? What if I ran the wires close together, as in zip cord or speaker wire? I've read various things and am a little confused.