Applying NEC Article 300

Article 300 requirements of the National Electrical Code (NEC) apply to all wiring installations, except as modified by articles in Chapter 5 [300.1]. How do you know what applies and what does not?

If you have a Chapter 5 installation, for example a motor fuel dispensing facility [514], what you want to do is apply Art. 300 but refer to Art. 514 as you go to see what’s modified. You’ll also be applying the requirements of Chapters 1 through 4 because they apply generally to all installations. Chapters 5 through 8 modify those requirements as applicable.

Article 300 is divided into two parts:

• Part I: For installations with a nominal voltage of 1,000V or less.
• Part II: For installations with a nominal voltage over 1,000V

These installations usually must be separate. Conductors with a nominal voltage over 1,000V cannot occupy the same equipment wiring enclosure, cable, or raceway with conductors that have a nominal voltage of 1,000V or less. However, in four situations this is permitted [303.3(C)(2)(a) through (d)].

For example, conductors of different voltage ratings are permitted in motors, transformers, switchgear, switchboards, control assemblies, and similar equipment [303.3(C)(2)(c)].