What to do about fiber optic cable trays entering low-voltage electrical shafts

Fiber optic cables can be run in cable trays in low-voltage electrical shafts, provided NEC requirements for separation, tray fill, and cable support are followed.NEC Compliance and Tray Use

According to NEC Article 392, cable trays are permitted for communications, control, and signaling circuits, including fiber optic cables, in any type of building if installation requirements are met . Fiber optic cables are nonconductive, so they do not carry electrical current, which allows them to share trays with other low-voltage circuits rated 600 volts or less without additional separation . Tray-rated fiber optic cables are preferred to ensure mechanical protection and long-term durability .

Separation and Signal Integrity

Even in low-voltage shafts, care must be taken to avoid interference from nearby power or limited-energy circuits. NEC 2026 and TIA-569-E recommend maintaining physical separation or using metallic barriers when power and communication cables share a tray . For low-voltage circuits (Class 2/3), fiber optic cables can typically share the same tray without a barrier, but divider brackets or compartmentalized trays are recommended in congested or mixed-voltage installations to protect signal integrity .

Tray Fill and Support

Cable trays must not be overfilled, as this can cause mechanical stress, heat buildup, or damage to the fiber jacket . Fiber optic cables should be secured at intervals according to manufacturer instructions, and the tray should provide adequate support along its length . Ladder, trough, or solid-bottom trays are all acceptable, but the choice depends on cable density and accessibility .

Best Practices

• Use tray-rated fiber optic cables for mechanical protection.
• Maintain proper separation from high-voltage circuits or use barriers if necessary.
• Ensure tray fill limits are not exceeded to prevent damage.
• Secure cables at recommended intervals to avoid sagging or stress.
• Metallic trays must be grounded and bonded to comply with NEC requirements . By following these guidelines, fiber optic cables can be safely and effectively installed in cable trays within low-voltage electrical shafts, ensuring both code compliance and long-term performance.