Optical Fiber Cables

Article 770 covers optical fiber cables and their raceways within premises. Fiber itself is dielectric — it moves data as light and carries no electrical current — so the shock and fire-from-current concerns are minimal. But the article exists because the physical cable still matters: its jacket contributes to a building's fire load, and fiber cables come in types that include conductive members.

It classifies fiber cable as nonconductive, conductive (containing non-current-carrying metal like strength members or armor), or composite (containing current-carrying electrical conductors bundled with the fiber). Each type has listing and installation rules, plenum/riser/general ratings mirroring the copper cable world, and separation requirements — especially keeping conductive and composite cables from creating a path to energized parts. Like 725 and 800, it requires removing abandoned cable to cut fire load. It set the template that Chapter 8's communications articles now largely reference for fiber.

When it applies

Article 770 covers optical fiber cables and their raceways inside buildings. Fiber itself carries light, not current, but the article still matters because some cables are conductive, they include a metal strength member or armor, and because plenum, riser, and general-use flame ratings govern where a given jacket may run.

Common mistakes

• Treating conductive fiber, the kind with a metal member, like nonconductive, conductive fiber has to be bonded and kept away from power conductors just like other metal.
• Running a general-purpose-rated fiber jacket in a plenum or riser that demands the higher flame rating.
• Abandoning old cable in ceilings, accessible unused cable is supposed to be removed.

In the field

The first thing I check on a fiber pull is whether the cable is conductive or all-dielectric. All-dielectric gives me the most freedom near power, but the moment there is a metal member in the jacket, it needs bonding and separation like any other metallic run.