If not designed and installed properly, wiring inside cable trays may pose hazards such as fire, electric shock, and arc-flash blast events. 305(a)(3), or comparable standards promulgated by States. The primary rulebook used in the safe use of cable trays is NEC Article 392. This is a description of how to select, install, and support these metal or plastic frames, on which electrical wires are installed. NEC section 300-8 does not permit any tube, pipe, or equal for water, air gas, drainage, steam, or any service other than electrical in raceways or cable trays containing. Cable tray is the preferred wiring method for industrial facilities, data centers, and large commercial buildings where routing dozens or hundreds of cables through individual conduits would be impractical and expensive.