Cables cannot be placed in cable trays
Not all cables or utilities can be installed in cable trays; only approved tray-rated electrical cables are permitted, while pipes, tubing, and non-electrical services are prohibited.
Prohibited Installations
Cable trays are designed specifically to support electrical conductors, including power, control, signal, and communication cables. According to NEC Section 300-8, mechanical utility piping or tubing containing water, compressed air, gas, drainage, or steam cannot be installed in cable trays that contain electrical conductors . This ensures safety by preventing potential hazards such as electrical shorts, corrosion, or interference.
Cable Restrictions
Only approved tray-rated cables should be installed in cable trays. These include:
- Tray-rated power cables (Type TC)
- Metal-clad cables (Type MC)
- Control and communication cables designed for open-air environments Cables that are not rated for open-air or tray use, such as standard non-metallic sheathed cables or single-conductor cables smaller than 1/0 AWG (except under specific industrial conditions), are generally not allowed in cable trays . Using unapproved cables can lead to overheating, fire hazards, or code violations.
Environmental and Design Considerations
Certain areas are also prohibited for cable tray installation, including:
- Hoistways or enclosed spaces
- Locations where trays would be inaccessible for maintenance Additionally, cable trays must maintain proper fill limits (typically 40% for power cables and 50% for control cables) and separation between high-power and low-power cables to prevent electromagnetic interference . Solid-bottom trays, while providing protection, have stricter fill limits due to reduced heat dissipation.
Summary
In short, cable trays are exclusively for electrical conductors that are rated for tray use. Non-electrical utilities, unapproved cables, and certain small single-conductor cables cannot be installed in cable trays. Adhering to these restrictions ensures compliance with NEC standards, prevents hazards, and maintains the integrity of the electrical system .
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