Communication Systems
What to master
Articles 800 through 840 cover the low-voltage wiring that shares buildings with power: communications circuits (800), radio and TV antennas (810), community antenna and cable TV systems (820), network-powered broadband (830), and premises-powered broadband (840). Focus on three themes. First, separation: communications cables must maintain at least 2 in of separation from power conductors unless a barrier is used, and they cannot be installed in the same raceway with power conductors unless listed for the purpose. Second, protection: a listed primary protector is required where the cable enters the building, and it must be grounded per 800.100 to a grounding electrode system. Third, markings: cable listings such as CM, CMR, CMP, and CMX describe rising fire resistance, and the location dictates which one is legal.
Traps
Using an unlisted cable in a plenum; forgetting separation from power feeders; confusing CATV grounding with the power system's grounded conductor; and assuming low-voltage means no permit or no inspection.
Worked example
A communications cable crosses a feeder in a commercial hallway. The installer leaves 1 in of clearance. That fails 800.130, which requires 2 in of separation unless a permanent barrier separates them - so the fix is either more clearance or a listed barrier.