Requirements for laying optical cables on cable trays

Optical fiber cables can be installed in cable trays if they are listed for use, with attention to bend radius, mechanical protection, and separation from power cables.

Regulatory Compliance

According to the National Electric Code (NEC), any listed optical fiber cable is acceptable for installation in a cable tray, as there is no specific tray rating required for fiber optics.

NE

C sections 300-8 and 318-5 provide guidance on cable separation: instrumentation, signal, and telecommunications cables should be separated from power cables to prevent electromagnetic interference and cross-talk. For cables rated over 600 volts, additional separation criteria apply.

Cable Tray Types and Installation

Cable trays come in several types: ladder, trough, channel, and solid-bottom trays. Ladder trays are common for industrial applications, providing good ventilation and easy access, while solid-bottom trays are used where heat buildup is minimal. Rung spacing of 150–230 mm (6–9 inches) is recommended to support cables and maintain proper bend radius.

Cable trays can be installed horizontally or vertically, with no difference in fill requirements, but cables must be securely fastened.

Mechanical Handling and Protection

During installation, optical fiber cables must be handled carefully to avoid damage: Bend radius: Minimum bend radius under tension is typically 20 times the cable diameter, and after installation, 10 times the diameter. Pulling and routing: Avoid sharp turns, kinks, and pulling over edges. Use smooth curves and figure-8 loops for long pulls to prevent twisting.

Environmental protection: If cables are exposed outdoors during installation for more than 24 hours, protective material should be used to prevent damage. Mechanical pressure: Minimize pressure at crossing points, especially for armored or LSZH cables, to prevent sheath cracking.

Separation and Segregation

To reduce noise and interference, power and communication cables should be separated either by using separate trays or dividers within a tray. Multiconductor cables rated 600 volts or less may share a tray, but separation from high-voltage or motor power circuits is recommended.

Additional Considerations

Follow the manufacturer's installation guidelines for pulling tension, temperature limits, and storage conditions. Ensure the tray material and finish are suitable for the environment, considering corrosion resistance and mechanical strength. Complete the installation in a single pull when possible to avoid splicing and additional stress on fibers.

By adhering to these requirements, optical fiber cables can be safely and efficiently installed on cable trays, ensuring long-term performance and compliance with industry standards.