Based on the 2008 NEC
National Electrical Code Articles and Information
National Electrical Code Top Ten Tips: Article 503 -- Class III Hazardous Locations
- The definitions of Class I, Class II, and Class III locations are
in Article 500.5. That's easy enough to remember.
- The general requirements (NEC Chapters 1 through 4) still apply to
Hazardous locations--except as specifically modified in Chapter 5.
- Equipment installed in Class III locations must be able to function
without getting hot enough to cause spontaneous
- The requirements for wiring methods are in 503.10. These differ
from Class I and Class II methods.
- The definition of "dusttight" is in Article 100.
- Per 503.4, you must use dustight enclosures for circuit breakers,
fuses, motor controllers, pushbuttons, relays, switches, and other devices intended to
interrupt current during normal operation.
- Ditto for control transformers.
- The special requirements for motors and generators are in
- Luminaires have special requirements, as outlined in 503.9. Other
devices, such as flexible cords, plugs, and receptacles also have
special requirements. Refer to the appropriate part of 503.
- Per 503.16, wiring and equipment in Class III locations must be grounded and
bonded as specified in Article 250, but with additional
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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.