Wiley Electronics’ Washer, Electrical Equipment Bond (WEEB) bonds modules to racks; the racks are then bonded together to create an EGC that is eventually bonded to the other pieces of equipment, generally via a rooftop combiner box. Additional language to Section 690.43 seems to support using WEEB grounding clips and the use of the racks as the EGC, and the PV community has accepted WEEB products, but not universally. This ambiguity is not surprising since the subject matter is grounding, but it is also based on concerns such as the appropriateness of the UL listing used to test WEEB products and the lack of testing by individual module manufacturers. Ultimately, the question is whether the WEEB grounding solution is acceptable to your AHJ.
System grounding. With the 2008 Code requirements, system grounding is one of the most discussed and debated topics within the installer community. When the first grid-tied inverters were introduced to the U.S. market, it was difficult to make a connection from the inverter to the system ground: Today, all grid-tied inverters have ground lugs large enough to run a grounding electrode conductor (GEC) to the existing grounding system.
Section 690.47 deals specifically with system grounding. This section was completely rewritten in the 2008 Code, and again in 2011 resulting in a number of differing opinions and methodologies. For example, a requirement in 690.47(C) is to size the DC GEC according to Section 250.166. This results in specifying an 8 AWG conductor or larger.
It is common to have grounding conductors serve as both the EGC and the GEC, allowable as long as the conductor is sized appropriately. For example, if a 7,000 W inverter is connected to a 40 A breaker within a main service panel, a minimum 10 AWG copper EGC is required per Section 250.122. However, according to Section 250.166, the GEC must not be smaller than 8 AWG. Therefore, for a single conductor to serve both purposes, it needs to be a continuous conductor no smaller than 8 AWG. Any EGCs connected to this conductor may not break the continuous GEC. In situations where this is not possible, it is necessary to run two separate conductors, one for the EGC and one for the GEC.
Electrical code violations receive the most attention when it comes to PV systems, but structural issues require examining the method of physically attaching PV arrays to roofs, poles, or the ground.
Most building departments use the IBC reference book, which, like the NEC, is published every three years with the 2009 IBC being most recent. The IBC requires compliance with attachment methods (modules to racks and racks to roof), as well as with equipment installation instructions. Properly flashing all roof penetrations, including structural attachments, is also required.
Although the IBC covers most of the structural issues that relate to PV installation, many local jurisdictions have specialty codes that go beyond these requirements. In areas with heavy snow loading, for example, a building department may require that installers evaluate the potential effects of snow drift and the additional dead load imposed by the PV array. In areas of high wind, the dynamic effect of wind needs to be evaluated and properly mitigated.
Attachment and placement. Correctly locating support rails as specified by the module manufacturer is also important. Many module warranties may be void if the manufacturer’s specified support and attachment methods are not followed.
Module-handling methods are another issue. It is not uncommon to see work crews grabbing a module by one side and carrying it to the final location. While this is not a Code violation, former PV module engineer Diana Buttz points out that “carrying the module in this fashion puts an enormous amount of pressure and torque on that edge and can lead to seal failure.” The correct way to carry modules, she explains, is to support both sides of the frame to minimize that stress.
Module placement and layout are critical, and often overlooked. For roof-mounted arrays, although not specified by the IBC, designing for adequate clearance is important. In its trainings, Sharp Solar recommends a minimum clear space of 12 inches around the array perimeter. When the modules are close to the roof eaves, 16 inches of clearance is recommended, which allows room for future service, and reduces wind uplift around the roof edges. To determine the exact requirements for your location, work with the racking manufacturer and local building and fire departments. They can verify clearances as well as dynamic load allowances like wind, snow, seismic activity, and so forth.
If installing a system that deviates from the roof plane, consult a structural engineer or the rack manufacturer’s engineers to evaluate the attachment method. However, the costs of engineering plus the additional racking materials may negate the value of the moderate increase in energy harvest.
As PV systems become common, AHJs will be further scrutinizing installations for compliance with national electrical and structural codes, as well as local codes.
Getting familiar with the codes can help your PV project get off to a good start. But you don’t necessarily have to wade through 840 pages of NEC technicalities to get there. Two great resources help sum up the most pertinent PV system code issues: First is the Solar America Board for Codes and Standards’ (Solar ABCs) “Expedited Permit Process for PV Systems,” which is available on the organization’s website. A concise 61 pages, the document walks through the most relevant issues, explaining the Articles that apply as well as the reasoning behind the standard. The document includes a fill-in-the-blanks schematic that you can tailor to your system and hand to your AHJ. Second, NEC expert John Wiles’ Photovoltaic Power Systems and the National Electrical Code: Suggested Practices can help you navigate the complicated world of the Code (see Access).
Ryan Mayfield is a NABCEP-certified PV installer and ISPQ Affiliated Master Trainer. When he isn’t trying to absorb all things solar, he is busy trying to influence the next generation by helping his kids solarize their backyard forts.
Burndy • www.burndy.com
ILSCO • www.ilsco.com
Tyco Electronics • www.tycoelectronics.com
Wiley Electronics • www.we-llc.com
National Fire Protection Association (NEC ) • www.nfpa.org
Solar America Board for Codes and Standards • www.solarabcs.org
Southwest Technology Development Institute • www.nmsu.edu/~tdi
Standard for Good Workmanship in Electrical Contracting (NECA 1-2006), National Electrical Contractors Association, 2006, paperback, 20 pages, $40 • www.necanet.org