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Applying NEC Article 300

Sept. 19, 2017
How do you know what applies and what does not?

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)].

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