Code Red: Notable Changes in the 2011 NEC
Inside this Article
Few articles are as subject to change from one Code cycle to the next as those applying to PV systems and interconnected power sources. Here is what is new and relevant to you in the 2011 edition of the NEC.
While the design and installation of PV systems requires knowledge that lies outside of the scope of the National Electrical Code, its requirements must be integrated into overall design practices. PV system design and installation are therefore affected by the many changes in the 2011 NEC.
While we focus mainly on PV-specific changes in the NEC, the Code also provides minimum standards for all electrical system installations that PV systems must meet, primarily relating to safety. However, merely meeting these minimum standards does not ensure that a PV system is efficient, easily expandable [90.1(B)] or aesthetically pleasing [110.12]. Designers and installers should consider these and other parameters in addition to safety. For example, the 2008 NEC required additional grounding electrodes at all ground- and pole-mounted PV arrays [690.47(D)]; this requirement has been removed from the 2011 Code. While no longer mandated, in many cases it is still a best practice because of the additional level of protection grounding electrodes provide to sensitive electronics.
The Code also includes Informational Notes (previously called Fine Print Notes), which are explanatory and nonmandatory, such as the recommendation that voltage drop in branch and feeder circuits not exceed 5% [210.19(A)(1) Informational Note No. 4 and 215.2(A)(4) Informational Note No. 2]. This is not a safety issue, but rather deals with system efficiency; therefore it is not mandated by Code. However, voltage drop is a critical design parameter for PV systems and in nearly all cases should not exceed 3% overall.
Other citations, such as 110.12, “Mechanical Execution of Work,” provide the AHJ with latitude to decide what qualifies as “neat and workmanlike.” One of the most overlooked but fundamental sections of the Code is 110.3(B), “Installation and Use,” which states, “Listed or labeled equipment shall be installed and used in accordance with any instructions included in the listing or labeling.” The use of lay-in lugs that are not rated for direct burial for module grounding is one common example of misusing a listed product. When an indoor-rated lug is improperly used outdoors, it invariably results in galvanic corrosion and poor grounding continuity.
PV-Specific Code Changes
While we strive to explain sometimes oblique Code changes, the final arbiter is always your local AHJ. The NEC is intended to be used by AHJs as a source of safety mandates for electrical installations. Ultimately, the local AHJ has the final authority in interpreting the Code, and for deciding which equipment and methods meet its requirements as per 90.4, “Enforcement.”
The majority of 690.4 pertains to mechanical specifics for PV installations. Noted Code experts Bill Brooks and Mike Holt agree that the changes in 690.4 are among the most important for PV system designers and installers to be aware of. (Brooks is principal at Brooks Engineering, and Holt is president and CEO of Mike Holt Enterprises.)
Identification and grouping. PV source and output circuits have historically been allowed to be contained in raceways, junction boxes and so on with other non-PV system conductors— if the conductors for different systems are separated by a partition. While this remains true, additions in 690.4(B) mandate identification and grouping of PV system conductors in all installations for added clarity.
As explained by Brooks: “The added identification and grouping requirements found in 690.4(B)(1) through (4) take requirements found elsewhere in the NEC and bring them specifically into 690. These are important changes due to the general lack of identification and grouping in existing systems. These deficiencies have resulted in several fires during system commissioning due to mispolarized wiring and poor identification practices.”