Overview of Chapter 8
Chapter 8 stands apart from the rest of the NEC in an important way: it is self-contained and independent of the preceding chapters unless a specific article within Chapter 8 references them. This means the general rules of Chapters 1 through 7 do not automatically apply to communications systems. Only the rules specifically referenced within Chapter 8 articles, plus Article 100 definitions and certain grounding requirements, carry over.
Exam Tip: The self-contained nature of Chapter 8 is itself a frequently tested concept. Remember that Chapter 8 rules apply independently, and only the sections of Chapters 1-7 that are specifically referenced within Chapter 8 are applicable.
Communications Circuits (Article 800)
Article 800 covers telephone, data, and other communications circuits that extend beyond one building or are connected to a central office or similar network.
Listing and Installation
- Communications cables must be listed for their intended use and location.
- Cable types are designated by their fire-resistance properties and permitted installation locations:
- CMP (Plenum): Suitable for use in ducts, plenums, and other spaces used for environmental air. Highest fire-resistance rating.
- CMR (Riser): Suitable for vertical runs between floors. Adequate fire resistance to prevent floor-to-floor fire spread.
- CMG/CM (General purpose): Suitable for general use within a building.
- CMX: Limited use, suitable for dwellings and raceways.
Separation from Power Conductors
- Communications conductors must not be placed in the same raceway, cable, or enclosure with power or Class 1 circuit conductors unless separated by a permanent barrier or where the power conductors operate at less than specified voltage limits.
- A minimum separation of 50mm (2 inches) is generally required between communications cables and power conductors in open installations.
Grounding Requirements
- The metallic sheath of communications cables entering a building must be grounded as close as practicable to the point of entrance.
- The primary protector (where required) must be listed and must be connected to a grounding electrode through a grounding conductor.
- The grounding electrode conductor for communications must be copper or other corrosion-resistant conductive material, not smaller than 14 AWG and not required to be larger than 6 AWG.
Intersystem Bonding
An intersystem bonding termination must be provided external to enclosures at the service equipment or metering equipment. This termination must be accessible and must accommodate the connection of grounding conductors from communications, CATV, and other systems. It ensures that all system grounds are bonded together to prevent dangerous potential differences.
Radio and Television Equipment (Article 810)
Article 810 covers receiving and amateur radio transmitting equipment, including antenna systems.
- Outdoor antennas and lead-in conductors must be kept away from power conductors and must maintain specific clearances from buildings and other structures.
- Antenna discharge units (lightning arrestors) must be installed on each lead-in conductor and must be grounded.
- The grounding conductor for antenna systems must be copper, aluminum, copper-clad steel, bronze, or similar corrosion-resistant material, and must be run in as straight a line as practicable to the grounding electrode.
- Amateur radio transmitting stations have additional requirements for conductor sizing and antenna support structures based on the power levels involved.
CATV Systems (Article 820)
Article 820 governs community antenna television (CATV) and radio distribution systems using coaxial cable.
- The outer conductive shield of coaxial cable must be grounded as close as practicable to the point of entrance to the building.
- CATV cables use a listing hierarchy similar to communications cables: CATVP (Plenum), CATVR (Riser), and CATV (General purpose).
- Coaxial cables must maintain the same separation requirements from power conductors as communications cables.
- The grounding electrode and bonding requirements mirror those of Article 800, ensuring all low-voltage systems share a common grounding reference.
Network-Powered Broadband (Article 830)
Article 830 covers systems that deliver both power and broadband signals over the same cable, typically provided by a utility or service provider.
- Circuits are classified based on voltage and power levels, which determine the applicable installation rules.
- Network-powered broadband cables must be listed and are classified as BLP (Plenum), BLR (Riser), or BL (General purpose) based on fire-resistance requirements.
- Primary protectors and grounding requirements apply similarly to those in Article 800.
Premises-Powered Broadband (Article 840)
Article 840 addresses broadband communications systems powered from the premises rather than the network. This includes fiber-to-the-premises installations where the optical network terminal is powered locally.
- Optical fiber cables are classified by their fire-resistance rating: OFNP/OFCP (Plenum), OFNR/OFCR (Riser), and OFN/OFC (General purpose).
- While optical fiber itself does not conduct electricity, composite cables containing both fiber and metallic conductors must meet grounding and bonding requirements.
- The metallic members of optical fiber cables entering a building must be grounded as close as practicable to the point of entrance.
Key Concept: The cable hierarchy system (plenum, riser, general purpose) is consistent across all Chapter 8 articles. A cable rated for a more demanding application (e.g., plenum) is always permitted to substitute for a less demanding application (e.g., general purpose), but not vice versa.
