Grounding requirements for main trunk optical cables

Trunk optical cables with metallic components must be grounded according to NEC Article 770, while fully dielectric cables require no grounding.

Key Principles

Fiber optic cables are primarily non-conductive, transmitting data as light rather than electrical signals. Dielectric (non-metallic) cables do not require grounding because they pose no electrical hazard and are naturally immune to electromagnetic interference (EMI) and lightning-induced currents . In contrast, armored or metallic fiber optic cables—which may include steel armoring, copper strength members, aluminum moisture barriers, or metallic messenger wires—must be grounded to prevent electric shock, equipment damage, and fire hazards .

Applicable Standards

• National Electrical Code (NEC) Article 770.93 and 770.100: Specifies grounding or interruption of non-current-carrying metallic members of optical fiber cables at building entry points or exterior terminations .
• NFPA 70: Provides binding requirements for safe installation.
• TIA and IEEE standards: Offer additional guidance for bonding and grounding practices in commercial and industrial installations .

NEC 770.93 Requirements

1. Entering Buildings (770.93 A): Metallic members exposed to contact with power conductors must be grounded at the point of entry or interrupted by an insulating joint. Grounding should be as close as practicable to the entrance.
2. Exterior Terminations (770.93 B): Metallic members terminating outside a building must be grounded or interrupted similarly, ensuring a low-resistance path to earth .

Practical Grounding Steps for Metallic Fiber Cables

1. Identify metallic components: Strip back 6–8 inches of the outer jacket to expose armor, strength members, or foil layers .
2. Clean the bonding surface: Remove oxidation or coatings using a wire brush or fine sandpaper to ensure low-resistance contact.
3. Attach a listed bonding clamp: Use a UL-listed clamp or manufacturer-supplied grounding kit to secure the metallic component.
4. Connect the grounding conductor: Run a minimum 14 AWG copper wire (or as specified by local code) from the clamp to the nearest grounding electrode or equipment grounding bus. Keep the path short and direct to minimize impedance .

Additional Considerations

• Metallic conduit or trays carrying fiber optic cables must also be grounded, independent of the cable type .
• Dielectric cables do not require grounding, but grounding practices may still be applied at the designer's discretion for safety or bonding continuity .
• Insulating joints can be used to interrupt metallic members, eliminating the need for grounding when exposure to power conductors is unavoidable .

Summary

• Dielectric fiber optic cables: No grounding required.
• Metallic or armored fiber optic cables: Ground at building entry points and exterior terminations according to NEC 770.93 and 770.100.
• Conduits and trays: Ground metallic pathways carrying fiber optic cables.
• Best practice: Always verify cable datasheets for metallic content and follow manufacturer-supplied grounding kits to ensure compliance and safety . This approach ensures both personnel safety and network reliability while meeting regulatory requirements.