I've seen different manufactures use different methods. Without recalling aircraft types, I've seen trays, conduit, and tubes.
On commercial aircraft, the norm is to not have the wire bundle enclosed in anything. Tie-wraps and tie-cord to hold the wires together, clamps to hold the whole bundle to structure.
As I have been finding lately, older wires break down. After isolating problem locations with the TDR and Fox/Hound, bundles have to be split open to find a specific wire. If the cable runs were in a tube or enclosed conduit, the job would be much more difficult.
