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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 5

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. One of the first steps when sizing conductors and overcurrent devices is to characterize the load. You must determine if it's continuous or noncontinuous. All PV system currents are continuous [690.8(B)].
     
  2. Overcurrent devices for PV systems must carry 125% of the calculated maximum currents [690.8(B)(1)(a)].
     
  3. When sizing overcurrent devices for PV systems, apply the temperature limits of 110.3(B) and 110.10(C). This requirement is in [690.8(B)(1)(b)].
     
  4. Conductors for PV systems must be sized to carry 125% of the calculated maximum currents, without any additional correction factors for the conditions of use. But if applying the correction factors results in a bigger number then you must size the conductors for that bigger number [690.8(B)(2)].
     
  5. If you have a common-return conductor for a PV power source with multiple output circuit voltages, the ampacity of the common-return conductor must be at least the sum of the ampere ratings of the overcurrent devices of the individual circuits [690.8(C)].
     
  6. If you use a single overcurrent device to protect parallel-connected module circuits, the module interconnection conductors must have an ampacity at least that of the rating fuse plus 125% of the short-circuit current from the connected modules [690.8(D)].
     
  7. Apply Article 240 when providing overcurrent protection to PV source circuits, PV output circuits, inverter output circuits, and storage battery conductors [690.9(A)].
     
  8. If a power transformer has a source on each side, you must treat each side as the primary when sizing the overcurrrent protection for each side [690.8(B)].
     
  9. If you have a utility connection, then obviously the premises wiring must meet the requirements of the NEC. Absence of such a connection doesn't waive this requirement. If the PV system is the stand-alone power source, the premises wiring must still meet Code [690.10]. It's not about pleasing the utility; it's about preventing fire.
     
  10. As with (for example) a standard, utility-connected residential service (or other occupancy), the supply can be less than the calculated load. The ac output from a standalone inverter (or inverter array) can supply power to the structure at less than the calculated load connected to that disconnect [690.10(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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