Low-Voltage, Communications, and Signaling Systems
Domain 8 covers Chapter 8 communications circuits, Article 725 Class 1, 2, and 3 circuits, Article 760 fire alarm systems, and Article 411 low-voltage lighting. The rules differ from power wiring, and the exam tests whether you recognize when that is true.
Chapter 8 independence
90.3 states that Chapter 8 installations need not comply with Chapters 1 through 7 except where Chapter 8 says so. A communications raceway is therefore not automatically required to satisfy Chapter 3, and cables need not follow Chapter 3 wiring methods - but the separation, listing, and grounding rules of Article 800 always apply.
Separation and cable ratings
800.133 requires at least 2 in of separation between communications cables and power conductors, or a barrier, and prohibits sharing a raceway or box with power conductors unless separated. Cables must carry the correct listing for the location: CMP in plenums, CMR in risers, CM for general use; Class 2 and 3 cables use CL3P, CL3R, and CL3 suffixes. 725.136 imposes similar separation rules for Class 2 and 3 circuits, and 760.130 governs fire alarm circuits.
Grounding and protection
800.100 sets the communications grounding electrode conductor at 10 AWG Cu minimum, run to the power grounding electrode system where available. 800.90 requires a listed primary protector for overhead drops. 820.100 applies the same bonding logic to coaxial cable.
Worked example
A cable TV coaxial cable enters through a basement wall. The shield must be bonded to the building's grounding electrode system with a conductor no smaller than 10 AWG Cu. A separate ground rod is acceptable only if it is bonded back to the power grounding electrode system with a conductor sized to 250.66, so the coax and the electrical service share one ground reference.
Traps
Assuming Chapter 8 must meet Chapter 3 raceway rules; running Class 2 thermostat wire through the same bored hole as NM cable without separation; using non-plenum cable above a return-air ceiling; grounding low-voltage equipment to a convenient water pipe without bonding; using an unlisted transformer for low-voltage lighting, where Article 411 requires a listed system.