Codes, Standards, and Referenced Documents
The document stack
NFPA 72, the National Fire Alarm and Signaling Code, governs design, installation, performance, and inspection/testing/maintenance of fire alarm systems. NFPA 70 (NEC) Article 760 governs the wiring method; Article 725 covers Class 2 and 3 circuits, and Articles 300, 310, and Chapter 9 tables supply general installation and conductor data. The occupancy code - NFPA 101 or the locally adopted building code - is what typically creates the requirement for a system. NFPA 90A and NFPA 92 address duct detectors and smoke control; NFPA 25 covers sprinkler system ITM, which is where supervisory device testing originates.
Where things live in NFPA 72
Fundamentals and power supplies, circuits and pathways, initiating devices, notification appliances, emergency control functions, protected-premises systems, documentation, and the inspection/testing/maintenance chapter. Chapter numbering was reorganized in recent editions, so always cite the edition.
Traps
Quoting "the code" without an edition. Assuming NFPA 72 mandates a fire alarm system - it does not; it tells you how to design and install one once another code requires it. Assuming the NEC controls coverage or audibility - it does not. Confusing power-limited fire alarm (PLFA) with non-power-limited fire alarm (NPLFA) circuit rules, which live in different parts of Article 760 and carry different wiring-method allowances.
Worked rule of thumb
NEC answers "how is it wired"; NFPA 72 answers "what is installed, where, and how must it perform." When two documents appear to conflict, check each scope article first; where a genuine conflict remains, the authority having jurisdiction resolves it, and the more restrictive requirement usually prevails.
Cable substitution
Listed cable substitution runs one direction only: a plenum-rated cable may replace a riser-rated or general-purpose cable, and a riser-rated cable may replace a general-purpose cable - never downward. A job specifying FPLR cable in a plenum return ceiling is noncompliant no matter how neatly it is installed.