NEC 2017 Updates for PV Systems

The 2017 edition of NFPA 70: National Electrical Code dramatically changes the practical safeguards for PV systems. It introduces more changes to Article 690, “Solar Photovoltaic (PV) Systems,” than any revision cycle since 1984, when the NEC first adopted Article 690.

Since the number of PV installations is booming, my colleagues and I on Code-Making Panel (CMP) 4—which oversees NEC Articles 225, 230, 690, 692, 694 and 705—understood that this was a critical revision cycle for NFPA 70. Thanks to the dedicated efforts of dozens of solar industry stakeholders who proposed a solid set of Code changes, the development process for NEC 2017 was very productive.

From a purely statistical perspective, for example, CMP 4 reduced the word count in Article 690 by more than 20%, from nearly 11,000 words in NEC 2014 to just over 8,000 words in NEC 2017. This streamlining is even more impressive when you consider that rapid-shutdown requirements in Section 690.12 actually increased ninefold, from 133 words in the 2014 edition to more than 1,100 words in 2017. Excluding 690.12, CMP 4 actually managed to reduce the length of Article 690 by nearly 30%.

In this article, I explain how it was possible to simplify Article 690 so dramatically. I also preview the Code revisions that are most relevant to PV system designers and installers, and explore how some of these changes will expedite permitting, inspection and O&M activities. Though the National Fire Protection Association (NFPA) will not formally adopt NEC 2017 until its technical meeting in June 2016, the development process is substantially complete. Therefore, the excerpts I present here are unlikely to vary substantially from the published standard. Based on previous revision cycles, the NFPA will start shipping NEC 2017 to customers around October 2016.

Narrowed Scope and Definition

For more than 30 years, Article 690 has covered numerous topics that are beyond the scope of the PV generating system. These items include dc loads, ac loads in stand-alone systems and battery storage systems. As part of the 2017 revision cycle, the DC Task Group of the NEC Correlating Committee proposed adding new articles to the Code. These new articles appear in Chapter 7, “Special Conditions,” and deal specifically with energy storage systems (Article 706), stand-alone systems (Article 710) and dc microgrids (Article 712). With the advent of the new articles, CMP 4 was able to strip out extraneous materials from Article 690. It also eliminated redundant sections in 690 that duplicated language from Article 692, “Fuel Cell Systems,” and Article 694, “Wind Electric Systems.”

As members of CMP 4 worked to narrow the scope of Article 690, we realized it was imperative that we define the term PV system much more clearly. If you ask different industry professionals to identify where a PV system starts and stops, you will get different answers—which is a problem. To deal with this inconsistency, CMP 4 introduced a new set of figures to Section 690.1 and a new definition in 690.13.

PV system disconnect. In NEC 2017, Section 690.13 clarifies that the PV system disconnect is the disconnecting means that separates the PV system conductors from all other conductors associated with all other electrical systems. In this context, other electrical systems include energy storage systems, multimode inverters, wind systems, load distribution wiring and so forth. The diagrams in Figure 1 and Figure 2 indicate where the PV system disconnect is located in a variety of system configurations and architectures. 

Note that the PV system disconnect in these diagrams is not always located at the end of what we traditionally think of as the PV system. On one hand, the PV system disconnect location is relatively self-evident in interactive and ac module systems. The PV system disconnect locations in Figure 1, for example, correspond with what we think of as the end of the PV system. On the other hand, the PV system disconnect location is more obscure in multi-module and stand-alone systems. As the complexity of the electrical power system increases, the PV system disconnect may not be located at what we think of as the end of the electrical system, as shown in Figure 2.

To identify the PV system disconnect in these complex electrical systems, you need to differentiate between conductors associated with different power sources. In dc-coupled multimode and stand-alone systems, for instance, we have traditionally considered the inverter and energy storage components as part of the PV system. Now, separate Code articles cover energy storage systems and PV power systems. This change means that the PV system disconnect is necessarily located upstream from energy storage conductors and equipment, perhaps at a charge-controller circuit breaker or similar. In an ac-coupled multimode system, meanwhile, the PV system disconnect is necessarily located upstream from any utilization load circuits. Here again, the energy storage and multimode inverter components are no longer defined as part of the PV power system.

By more narrowly defining the scope and definition of a PV power system, CMP 4 was able to eliminate the source of much confusion in Article 690 and remove language duplicated in other articles. While the new figures in Section 690.1(B) by no means present an exhaustive treatment of the many possible system permutations, they provide good guidance regarding the PV system disconnect location. Simply put, if you open what you think is the PV system disconnecting means and look toward the PV array, there should be no other conductors or equipment from other electrical systems on the PV side of that disconnect. If conductors and equipment associated with other power sources and electrical systems are upstream, then you are not at the PV system disconnect. Keep moving toward the array until you are at a location where there are clearly no other electrical systems on the array side of the switch.

Pages

Article Discussion