National Electrical Code ExplanationsBased on the 2014 NECby Mark
Lamendola
National Electrical Code Tips: Article 725, Class 1, Class 2, and Class 3 Circuits. Part 2.
- Part II of Article 725 provides the requirements for Class 1 circuits. However, Part II provides the requirements for both Class 2 and Class 3 circuits. Why is Class 1 by itself, and the other two are together? It has to do with the power limitations. These make the requirements for Class 2 and Class 3 very similar to each other, but they make the requirements for Class 1 enough different from the other two that it Class 1 needs to be addressed separately.
- A Class 1 power-limited circuit is one supplied by a source with a rated output of not more than 30V and 1kVA [725.41(A)].
- A Class 1 remote-control or signaling circuit is a circuit that's used for remote-control or signaling and operates at 600V or less [725.41(B)].
- The requirements for Class 1 power sources are in 725.41(A).
- If the conductors are 14AWG or larger, provide overcurrent protection the normal way; except you don't apply the ampacity adjustment and correction factors of 310.15 to the ampacity calculation [725.43].
- Overcurrent protection can't exceed 7A for 18AWG conductors or 10A for 16AWG conductors [725.43]. Except as permitted by other Articles.
- Install OCPDs at the point where the conductors receives their supply [725.45(A).
- You can use branch and feeder taps, if you follow specific rules pertaining to them nt [725.45(B) and (C)].
- Install Class 1 circuits using the appropriate Articles from Chapter 3 [725.46].
- You can install Class 1 conductors with other circuits, if you meet the applicable requirements specified in 725.48.
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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.
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