Cable trays are classified as mechanical support systems for wiring methods, not as raceways, and are governed by NEC Article 392.

Classification and Purpose

Cable trays are rigid structural systems used to support and route electrical cables, raceways, and boxes in commercial, industrial, and institutional buildings (NEC 392.2) . They provide a flexible alternative to conduit systems, allowing easy installation, maintenance, and future expansion of power, control, and communication wiring . Cable trays are not considered raceways, which are enclosed channels designed specifically to hold wires or busbars . Instead, they function as a support system for wiring methods.

Permitted Wiring Methods

According to NEC 392.10, cable trays can contain:

• Service, feeder, and branch-circuit conductors
• Control, signal, and communications cables
• Single insulated conductors (in industrial establishments under specific conditions) Control, signal, and communication cables must be separated from power conductors by a barrier or maintain a minimum 2-inch separation . Only cables and raceways listed and marked for use in cable trays are permitted, and hazardous locations require compliance with NEC cable type restrictions .

Types of Cable Trays

Cable trays come in various configurations, including:

• Ladder trays – support cables on rungs, allowing ventilation
• Ventilated troughs or channels – allow airflow and dust drainage
• Solid-bottom trays – provide maximum protection for cables
• Wire mesh trays – lightweight and flexible for smaller cables Materials include galvanized steel, stainless steel, aluminum, and fiber-reinforced plastic, chosen based on environmental conditions and electrical requirements .

Installation and Code Considerations

• Cable trays must be installed as a complete system with maintained electrical continuity and proper support .
• Fill limits are specified by NEC Sections 392.11 and 392.13 to prevent overloading and ensure safe ampacity .
• Cable trays are not permitted in hoistways or areas subject to severe physical damage .
• They are treated as a structural component of the electrical system, supporting cables similarly to how bridges support traffic .

Summary

Cable trays are mechanical support systems for wiring methods, not raceways, and are coded under NEC Article 392. They allow installation of various power, control, and communication cables while providing flexibility, accessibility, and compliance with safety and fill requirements. Their classification emphasizes support rather than enclosure, distinguishing them from conduit or other raceway systems.