Communication, Data, and Security Systems
Articles and cable markings
Article 800 covers communications circuits; Article 820 covers community antenna and cable TV; Article 830 covers network-powered broadband; Article 840 covers premises-powered broadband, including Power over Ethernet. Article 770 covers optical fiber. Copper cable is marked CM, CMR, or CMP with a voltage rating. Substitution runs downward only: CMP may replace CMR or CM, and CMR may replace CM, but not the reverse. Fiber follows the same logic with OFNP, OFNR, and OFN.
Installation rules
- 800.133 requires at least 2 in. of separation from power conductors, or a permanent barrier, in boxes and raceways.
- 300.22(C) requires CMP or OFNP cable in environmental air spaces.
- Channel length is 100 m total, typically 90 m permanent link plus patch cords, per TIA-568.
- Follow manufacturer bend radius and TIA-569 support practices; do not staple Category cable.
- Bundled PoE cables can overheat; 725.144 and its table address ampacity in bundles.
Worked example
A designer routes 60 Category 6A cables through a return-air ceiling and proposes CM cable to cut cost. Reasoning: the ceiling is an environmental air space under 300.22(C), so the minimum is CMP. CM is not a permitted substitute there; CMP is permitted anywhere CM or CMR is allowed, so the correct specification is CMP.
Traps
- Substituting CM for CMP in a plenum.
- Running communications cable with power and no barrier.
- Ignoring the 100 m channel limit.
- Forgetting that security devices often use Class 2 or 3 circuits with Article 725 separation rules.