National Electrical Code Tips: Article 725, Class 1, Class 2, and Class 3 Circuits. Part 2.

1. Part II of Article 725 provides the requirements for Class 1 circuits. However, Part III 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.
   
2. 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)].
   
3. 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)].
   
4. The requirements for Class 1 power sources are in 725.41(A).
   
   
   
   
   
5. 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].
   
6. Overcurrent protection can't exceed 7A for 18AWG conductors or 10A for 16AWG conductors [725.43]. Except as permitted by other Articles.
   
7. Install OCPDs at the point where the conductors receive their supply [725.45(A)]. This is generally true of all circuits and because of that the OCPD defines the circuit.
   
8. You can use branch and feeder taps, if you follow specific rules pertaining to them [725.45(B) and (C)].
   
9. Install Class 1 circuits using the appropriate Articles from Chapter 3 [725.46].
   
10. You can install Class 1 conductors with other circuits, if you meet the applicable requirements specified in 725.48.

How the NEC is arranged

1. The first four Chapters of the NEC apply to all installations.
2. Article 90 precedes Chapter One, and establishes the authority of the NEC.
3. Article 80 follows the body of the NEC; it exists as Annex H. It provides the requirements for administration.
4. Chapters 5, 6, and 7 are the "special" chapters, covering special: occupancies, equipment, and conditions (in that order).
5. Chapter 8 provides the requirements for communications systems.
6. Chapter 9 provides tables.
7. The appendices provide mostly reference information.
8. 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.