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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 8

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. Connectors used in PV circuits must comply with 690.33. For the installer, this simply means you must use connectors listed for use with PV systems. The manufacturers of these connectors are the ones who must ensure the connectors comply with 690.33 so they can be listed for use in PV circuits.
     
  2. Be careful where and how you locate boxes. You can put junction, pull, and outlet boxes behind PV modules, but if you locate them there then you must make it so the wiring inside the box is directly accessible by dint of easily moving the PV module out of the way [690.34]. From an engineering and maintainability standpoint, you want to avoid this situation. But sometimes it may not be practical to due space considerations or other limitations.
     
  3. A PV system can have an ungrounded PV source and ungrounded output circuits. But only if you meet the conditions outlined in 690.35 (A) - (G). Note that "ungrounded" does not mean "metallic objects are not bonded." Systems not meeting the conditions of 690.35 (A) - (G) must be grounded and meet the requirements of Article 690, Part V (690.41 - 690.50) [690.41].
     




  4. Exposed non current-carrying equipment must be bonded, not "grounded" as stated in 690.43(A). See the Article 100 definitions of "bonding" and "grounding", Article 250 Part V, and the IEEE Green Book.
     
  5. You must install an equipment "grounding" (bonding) conductor between a PV array and other equipment [690.43(B)].
     
  6. Under specified conditions, you can use the structure as an equipment bonding conductor [690.43(C)].
     
  7. You have to run the equipment "grounding" (bonding) conductors in the same raceway (or cabling) where you run those conductors to a point outside the vicinity of the PV array [690.43(F)]. For example, if this is a supplemental power source for the building then you will need to bond the PV system's equipment "grounding" (bonding) system to the equipment "grounding" (bonding) system of the utility power or other bonding system. Do not drive a ground rod as a means of doing this; it does not electrically accomplish this purpose. Only the main equipment bonding jumper should connect to the grounding system; otherwise, you get ground loops that defeat the equipment bonding system.
     
  8. Size the equipment "grounding" (bonding) jumpers no smaller than what's specified in 690.45. You can size them larger, if you choose. But don't make the mistake of jamming oversized wires into the bonding lugs and assume that creates a better system. It actually creates differences in potential due to the poor connection. So don't oversize bonding conductors relative to the 690.45 requirements unless you can also upsize the connectors.
     
  9. Be careful when applying 690.47, "Grounding Electrode System." Remember, you cannot use the earth as a bonding jumper; attempts to do so create dangerous differences of potential. Grounding is mainly for lightning protection. All grounding electrodes (e.g., driven rods) must be bonded together. You cannot have "separate" grounding systems, because the "ground" (earth) is not at infinite resistance (permitting separation). Nor is it low resistance, permitting it to act as if it's a #4 copper wire.
     
  10. After misusing the term "grounding" in reference to bonding conductors, Article 690 finally uses the correct (per Article 100 and other references) terminology in 690.50. Don't let this confuse you into thinking there are equipment bonding jumpers to install in addition to equipment "grounding" conductors. What's happening here is the NEC is slowly correcting misuse of the word "grounding" with each revision. So you get these anomalies in terminology.

    To avoid confusion, always refer to the Article 100 definitions. And remember: You BOND equipment. You NEVER ground it. Even if grounding is a condition of warranty, don't do it. Such a requirement, because it violates the NEC, basic electrical engineering principles, and several authoritative references, is unenforceable.

    Just be sure to send the mfr a letter to this effect before there's a warranty claim. It will be helpful to draw out the circuit and show that, per the Law of Parallel Circuits, electricity takes all paths before it in inverse proportion to the impedance of each path to the total path impedance. It does not take "the path of least resistance," a myth that defies all we know about circuit design.

    Don't let the ignorance and incompetence of a manufacturer intimidate you into installing equipment in a manner that is certain to cause interruption in operations or even get people killed. Most manufacturers don't have this problem, but some do. It is ethically imperative that you install a safe installation.

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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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