The first four Chapters of the NEC apply to all installations, except as modified by Chapters 5, 6, 7, and 8. Chapter 7 modifies other Chapters when the installation is one of the “Special Conditions” covered in this Chapter.
So what’s a “condition" and what are the criteria that make it “special?” The answer emerges when you look at the Articles and how they are grouped.
- Group 1 — Special Power Systems (Articles 700 – 708): These are emergency systems (lighting and/or power supplied when the normal power is interrupted), legally required standby systems (as the name implies, a standby system that is required by law), optional standby systems (not required by law), interconnected power sources (in parallel with the primary source), and critical operations power systems (supply power to an area that a government entity has classed as “designated critical operations area”).
- Group 2 — Low-Voltage Systems (Articles 720 -727): These include circuits and equipment operating at less than 50V, circuits using a power-limited supply (Class 1, 2, and 3), and instrumentation cable tray. This grouping does not include lighting systems operating at 30V or less ; those systems are grouped close to the lighting-related requirements of Chapter 4.
- Group 3 — Certain fire-related systems (Articles 728 and 760): These are fire-resistive cable systems and fire alarm systems. This grouping does not include fire pumps , which are covered in Chapter 6 (Special Equipment).
Two types of equipment aren’t grouped with any other equipment: energy management systems  and optical fiber (cables and raceways) .