Fiber Optic and Network Cabling Installation Requirements (NEC Articles 770 and 800)
What this domain tests
Article 770 covers optical fiber cables; Article 800 covers communications circuits, which often include network cabling. The exam tests fiber cable markings, conductive versus nonconductive fiber, separation, support, bend radius, and the interface between fiber and copper network cabling.
Core rules
- Optical fiber cable markings: OFN general, OFNR riser, OFNP plenum. Use the rating that matches the space.
- Nonconductive fiber does not carry current, but it is not exempt from physical protection, support, bend radius, and firestopping rules.
- Conductive fiber, such as armored fiber or fiber with metallic members, may require grounding and bonding; follow the listing and Article 770.
- Network copper cabling is generally Article 800; keep it separated from power and use CM, CMR, or CMP correctly.
- Support cables at required intervals and do not exceed the manufacturer's bend radius; tight bends cause attenuation.
Worked example
A 12-strand fiber backbone runs through a plenum and then a riser. The plenum portion needs OFNP; the riser portion needs OFNR. If the cable has an armored metallic sheath, bond it as required by the listing and Article 770. The installer must also firestop the penetration and support the cable without cinching it.
Traps
- Assuming fiber has no rules because it is nonmetallic.
- Using OFNR in a plenum.
- Ignoring conductive fiber grounding.
- Overbending or over-tightening cable ties.