NEC Articles 725, 760, and 800: Circuit Classification and Wiring
What the exam tests
Articles 725, 760, and 800 divide low-voltage work by purpose, not by voltage alone. Article 725 covers Class 1, Class 2, and Class 3 remote-control and signaling circuits that are not fire alarm. Article 760 covers fire alarm systems and splits them into non-power-limited fire alarm (NPLFA) and power-limited fire alarm (PLFA). Article 800 covers communications circuits such as telephone, data, and coax. The exam asks you to classify a circuit first, then apply the wiring, listing, and separation rules for that article.
Core rules
- Class 1 circuits may be power-limited or non-power-limited; Class 2 and Class 3 are limited-energy circuits supplied by listed Class 2/3 power sources.
- PLFA conductors must be listed for fire alarm, typically FPL, FPLR, or FPLP; NPLFA wiring uses Chapter 3 methods with conductors rated for the voltage.
- PLFA and NPLFA must be separated from power and Class 1 circuits unless a listed barrier or other permitted method maintains separation.
- Article 800 communications cable must not be substituted for fire alarm cable; CL2/CL3 cable is not a fire alarm listing.
- Fire alarm circuit classification follows the system, not the wire color or the fact that it is 24 VDC.
Worked example
A 24 VDC notification appliance circuit is fed by a listed fire alarm power supply and uses FPLP cable. It is PLFA, so Article 760 Part III applies. A 120 VAC branch circuit cannot share the same raceway without a permitted barrier. If the same 24 VDC circuit were a Class 2 security circuit, Article 725 would apply instead.
Traps
Calling every 24 V circuit "Class 2"; using CL2/CL3 cable on a fire alarm NAC; treating NPLFA as if it were power-limited; and forgetting that Article 760, not Article 725, governs fire alarm circuits.