What type of cable tray should be used for the main runs of a cable tray wiring system?
The cable tray types to choose from are ladder, ventilated trough, or solid bottom. What are the reasons for selecting a specific type of cable tray?

The engineer or designer should select the type of cable tray that has the features which best serve the project’s requirements.

For a few types of installations, the National Electrical Code (NEC) specifies the cable tray type to be used:

Single conductor cables and Type MV cables must be installed in ladder or ventilated trough cable trays. Single conductor cables and Type MV cables are not allowed to be installed in solid bottom cable trays [1993 NEC Section 318-3(b)]

In Class II, Division 2 Hazardous (Classified) Locations (Dust), the types of cables that are allowed to be installed in cable trays must be in ladder or ventilated trough cable trays. Solid bottom cable trays are not allowed to be installed in Class II, Division 2 locations [1993 NEC Section 02-(b)].