Understanding NEC Article 840: Premises-Powered Broadband Communications Systems

NEC Article 840 addresses premises-powered broadband communications systems, which integrate voice, video, data, and interactive services into a unified infrastructure. These systems typically use premises-based power supplies, ensuring operational continuity even during power interruptions with battery backups or uninterruptible power supplies (UPS).

Scope of Article 840

This article applies to:

• Premises-powered broadband systems using optical fibers, twisted pairs, or coaxial cables.
• Network terminals that convert broadband signals into component signals such as telephone, video, and internet services​.

Informational Notes:

• Systems must ensure compliance with related articles like 725, 760, 770, 800, and 820 for wiring derived from the optical network terminal (ONT) into the premises.

Key Requirements for Premises-Powered Broadband Systems

1. Cables Entering and Exiting Buildings (840.47, 840.94)
   • Underground cables must have a minimum cover of 6 inches.
   • Circuits exiting a building must comply with lightning protection standards from NFPA 780 and grounding requirements in 805.93​.
2. Grounding and Bonding (840.93, 840.101)
   • Metallic components of optical fiber, coaxial, and communications cables must follow grounding methods outlined in related NEC articles.
   • Network terminals must be grounded unless explicitly exempted by product listings​.
3. Premises Circuits Leaving Buildings (840.102)
   • Such circuits must follow additional requirements for grounding and protection due to their exposure to external elements​.

Powering Circuits and Cabling

1. Power Over Communications Cables (840.160)
   • Communications cables may carry both communication signals and power, such as in Power over Ethernet (PoE) systems.
   • PoE installations must comply with 725.144 to prevent overheating from bundled cables​.
2. Rated Current Limits
   • Systems operating with conductors of 24 AWG or larger are exempt from 725.144 if current per conductor is limited to 0.3 amperes​.

Equipment and Listing Requirements (840.170)

1. Network Terminal
   • Terminals and grounding means must be listed for compatibility with premises-powered systems.
   • Listings include ANSI/UL 60950-1, ANSI/UL 467, and ANSI/UL 62368-1​.
2. Cables and Accessories
   • Wires and cables must be marked per 800.179, while accessory equipment must comply with ANSI/UL 1863.
3. Power Sources
   • Power sources must be listed as per 725.60(A) and meet limitations for voltage up to 60 V DC​.

Applications

NEC Article 840 ensures safe and efficient integration of premises-powered broadband systems in:

• Residential Areas: Providing TV, phone, and internet through network terminals.
• Commercial Properties: Supporting unified communications in offices and retail spaces.
• Industrial Facilities: Enhancing remote equipment operations and monitoring.

Conclusion

NEC Article 840 ensures the safety and functionality of premises-powered broadband communications systems. By emphasizing grounding, protection, and PoE compliance, it allows for robust and reliable integration of modern communication technologies.