Section 318-4 Uses Not Permitted states that “Cable tray systems shall not be used in environmental air spaces except as permitted in Section 300-22 to support wiring methods recognized for use in such spaces. The wiring methods allowed under Section 300-22 that utilize cable tray must follow the. Many modern buildings rely on cable trays to carry a lot of power and data lines. This isn't just about cables not lasting as long; it can also start fires. Unlike conduit systems, cable trays allow cables to be laid in bundles, improving accessibility, heat. The placement of cables, ducts, and conduits can be done using cable trays – for both outside plant (OSP) and interior spaces (ISP).