Everyone recognises that DCC does not deliver the "two wires are all you need" utopia. In this railway, the power has to be fed separately to a lot of track sections simply for train occupancy. That already implies a lot of wires. 

So what do you do? Early on I wrote a comprehensive "wiring rules" document. Having wired much of the railway and looked back, much of that was rubbish so it's been discarded.

Wiring falls into several classes; I've used a different approach to each.

Mains Wiring

A consistent rule from the start has been no mains wiring on the railway. That is an absolute. The mains wiring is limited to things that plug into distribution boards attached to the wall; these are fed from a single switch. There are no circumstances where a mains wire runs around under the baseboards; it just doesn't happen.

Structural Wiring

Structural wiring refers to DCC power feeds from the boosters, power feeds to the distributed electronics. These wires go to the panels around the layout with the distributed electronics, and I established a common connector wiring scheme for a 12 pin plug-on "chocolate block" connector. This allows power to be isolated if required. The structural wiring is generally made with brown/blue figure 8 mains cable. I'm satisfied this implies no safety risk; other may disagree in which case they are free to do differently!

Track Feeds

The power is zoned and block detected. This means there are over 100 power feeds, and 16 returns.

The returns are all lettered, and fed with a black wire. The feeds are numbered, and fed with an orange wire. (I had planned to use red, but the supplier was out of stock. I figured as long as it was consistent it didn't matter). All wires are labelled with their number or letter; I found some label sheets that could be laser printed then folded around the wire to provide an enduring record.

Points & Signals 

These are all controlled by 6 core 7/0.2mm stranded alarm wire. This is used either to power two adjacent points, or one signal. The wires are labelled with an indelible marker, but that may on reflection not be very reliable. For signals, the wire colour is matched to aspect with black being the common 0v return. Where two points are powered by one wire, I established the following colour convention:

red THROWN for lower numbered point
black common return
green CLOSED for lower numbered point
blue THROWN for higher numbered point
white common return
yellow CLOSED for higher numbered point