Article 90 precedes Chapter 1 of the NEC. Is it just boilerplate fluff, or should you become familiar with it? The answer is self-evident once you begin reading it.
Article 90 explains important concepts, such as:
• The purpose of the NEC. Understanding why we have the NEC in the first place goes a long way toward being able to apply it properly. A misunderstanding of its purpose is at the heart of many “code conflicts” in real applications.
• Its scope. Do you really know what the NEC covers and doesn’t cover? This, like its purpose, is an area commonly misunderstood.
• How it’s arranged. Can you name the supplemental chapters? Do you know what the NEC means by this? Do you know which Chapter isn’t subject to Chapters 1 through 4 except where specifically noted?
• The differences between mandatory rules, permissive rules, and explanatory material. Can you explain these off the top of your head?