Wiring methods for service conductors must be one of the 19 enumerated in Section 230.43 of the 2014 NEC. Interestingly, this list does not include cable trays. This would appear to mean they are excluded. But are they implied because cable bus is in that list?
The answer to this question is no. Cable bus (Art. 370) and Cable Tray (Art. 392) are two very different wiring methods. Unfortunately, there’s nothing in 230.43 to tell you to keep reading. If you do, you find the answer in the next subsection.
You can use cable trays to support service entrance conductors [230.44]. But there are limitations. These limitations don’t apply to the wiring methods enumerated in 230.43, so simply adding cable tray to that list would be confusing.
The solution currently in the NEC may be confusing if your approach to the NEC doesn’t include taking the time to read through the applicable Part (in this case, Part IV). It helps that the subsections tend to be grouped topically. So, for example, this cable bus requirement immediately follows the requirement pertaining to permitted wiring methods. Because Part IV ends on the page facing the one where you find 230.44, this isn’t a big time drain.
The NEC has remained quite well-organized despite big changes in materials and methods over the last dozen revision cycles.
