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National Electrical Code Articles and Information

Based on the 2011 NEC

by Mark Lamendola

National Electrical Code Tips: Article 690 -- Solar Photovoltaic Systems, Part 4

Only about 15% to 20% of the work of installing a Solar Photovoltaic (PV) System is electrical. But that electrical portion can easily result in disaster if not done correctly. Thus, Article 690 provides requirements for that portion.

  1. If you need to know the circuit requirements for PV systems, turn to Part II of Article 690. That's where they all are.
     
  2. In a dc PV source or output circuit, the maximum PV system voltage is something you calculate. It's the sum of the rated open-circuit voltage of the series connected PV modules (corrected for the lowest expected ambient temperature) [690.7(A)].
     
  3. For crystalline (and multicrystalline) silicon modules, you must multiply the rated circuit voltage by the correction factor in Table 690.7 [690.7(A)]. Use the result to determine the voltage of equipmetn such as cables and disconnects.




  4. DC utilization circuits must follow the branch circuit voltage requirements of 210.6 [690.7(B)].
     
  5. In one and two family dwellings, PV circuits (other than those that contain lampholders, fixtures, or receptacles) can have a maximum PV system voltage up to 600V [690.7(C)].
     
  6. In one and two family dwellings, live parts of PV circuits over 150V to ground can't be accessible to anyone other than qualified persons [690.7(D)].
     
  7. For 2-wire circuits connected to bipolar systems, the maximum voltage is the highest voltage between the conductors, if the three conditions of 690.7(E) apply. This means that if you can measure 150V between conductors you can't have one conductor measuring 180V to ground and the other measuring 30V to ground. Since one of the three conditions is that one conductor of each circuit be solidly grounded, any failure to comply means you have a grounding problem to troubleshoot.
     
  8. In addition to determining the maximum PV system voltage [690.7], you need to calculate the maximum current for each of four specific types of circuit [690.8(A)].
     
  9. A prerequisite to determining conductor ampacity and overcurrent protection size is that you must characterize the load. This may involve any of several engineering decisions, but it always involves determining if the load is continuous or noncontinuous. PV system currents are always considered continuous [690.8(B)].
     
  10. You must size overcurrent devices for PV systems to carry at least 125% of the maximum calculated current [690.8(B)(1)(a)].

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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.

 

 

 

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