Based on the 2008 NEC
National Electrical Code Articles and Information
National Electrical Code Top Ten Tips: Article 505 -- Class I, Zone 0, 1, and 2 Locations
- Article 505 covers the requirements for the zone classification
system as an alternative to the division classification system
covered in Article 500 for Class I, Zone 0, 1, and 2.
- Flameproof refers to keeping flames contained within the
enclosure, not whether something is flammable [505.2].
- If you use the zone system, you must generate and maintain
specific documentation [505.4]. The documentation requirements are
far from casual.
- Exactly how you may classify a location depends on the
properties of the flammable substances that may be present and on
their concentration [505.5].
- Class 1, Zone 0 basically means ignitible concentrations of
vapors or gases are consistently present [505.5(B)(1)].
- Class 1, Zone 1 basically means ignitible concentrations of
vapors or gases are likely to exist under normal operations
- Class 1, Zone 2 basically means ignitible concentrations of
vapors or gases are not likely to exist under normal
- Note that we have oversimplified the definitions of 0, 1, and 2
so that you can easily see how they differ. Read the references
thoroughly to understand the implications for a given location.
- Material Groups provide another twist. Which Material Group you
have depends on which specific gases you are dealing with.
- Once you know the exact classification and Material Group, you
must apply the applicable protection techniques from 505.8.
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Learn more about:
How the NEC is arranged
- The first four Chapters of the NEC apply to all installations.
- Article 90 precedes Chapter One, and establishes the authority of the NEC.
- Article 80 follows the body of the NEC; it exists as Annex H. It provides the requirements for administration.
- Chapters 5, 6, and 7 are the "special" chapters, covering special: occupancies, equipment, and conditions (in that order).
- Chapter 8 provides the requirements for communications systems.
- Chapter 9 provides tables.
- The appendices provide mostly reference information.
- Appendix D contains examples that every NEC user should study.
Try your NEC moxy:
- Do you know the difference between bonding and grounding? Hint: Look in the NEC, Article 100.
- Does the NEC refer to grounding incorrectly in any of its articles? Yes! So be careful to apply the Article 100 definitions. Don't ground where you should bond.
- When doing motor load calculations, which Article covers hermetic motors? Answer: While Article 440 covers the application of hermetic motors, it does so only by amending Article 430 because hermetic motors are a special case of motors. For motor load calculations, refer to Article 430.
- Does the NEC provide a voltage drop requirement? Yes! It does so in a special case, which is Article 648 Sensitive Electronic Equipment. But for general applications, it does not provide a requirement; it merely provides a recommendation in a couple of FPNs.
- Take our Code Quizzes.
Remember other applicable codes, rules, standards, and references:
- OSHA's electrical worker safety rules.
- IEEE standards.
- NETA standards.
- NFPA standards.
- International Codes (if applicable to the installation).
- State Codes (if the state has them).
- Local ordinances and permit requirements.
- Local fire codes.
- Manufacturer requirements or guidelines.
- Customer security requirements.
- Industry standards.
- Your company's own internal standards, practices, and procedures.
- Engineering drawing notes.