John Wiles, Southwest Technology Development Institute

Increasing PV System Safety and Code Compliance

John Wiles has been on the forefront of National Electrical Code–related PV training for more than two decades. He began writing Code sections specific to PV systems in 1990. In the last two Code cycles, Wiles, as secretary of the PV Industry Forum, has provided more than 60 proposals that have been accepted for inclusion in the NEC and the draft commentary that accompanies Article 690 of the NEC Handbook. Wiles is senior research engineer for the Southwest Technology Development Institute (SWTDI), a nonprofit organization located on the campus of New Mexico State University that provides applied research and development services for private and public sector clients. For decades, Wiles’ codes and standards development efforts, as well as the training he provides for PV system integrators, electrical contractors and inspectors, have had a fundamental and far-reaching impact on PV system safety and on Code compliance in North America.

SP: When did you first become involved with PV technology? What was the state of the industry at that time, and what drove your interest and involvement?
JW: I installed my first PV system in 1984 using some of the first listed PV modules manufactured by ARCO Solar and Solarex (ARCO eventually became SolarWorld USA, and Solarex was purchased by the recently deceased BP Solar). At that time, the PV industry was largely a group of long-haired off-grid solar hippies. The early editions of Home Power magazine provide a timely snapshot of the industry. After retiring from the US Air Force in 1989, I started my present career in the PV industry as a short-haired off-grid solar hippie. As a closet environmentalist, I could see the handwriting on the wall concerning limited global water, energy and food resources. As an electrical engineer, I decided to see how I could best help address these issues.

SP: How has the PV-specific content in the NEC changed over the last several cycles?
JW: The Code has changed incrementally over that time—hopefully for the better. The Code’s primary impact is that PV systems integrators, installers and electrical inspectors are becoming more aware of, and are more consistently applying, the numerous requirements described not only in Article 690, but also in the rest of the Code. New technologies like dc-to-dc converters, ac PV modules, dc PV arc-fault circuit interrupters and module level disconnects (coming in 2014) will continue to challenge code writers, PV installers and inspectors in the coming years.

SP: What are some of the persistent problems you see with PV installations?
JW: Improper grounding of modules and racks, and poor application of the utility-interface requirements. Workmanship issues revolving around conductor damage during installation are also showing up. In addition, I frequently see a lack of consistency among the electrical diagrams included in a project’s plan set, the requirements of the NEC and what the electrician actually installs.

SP: Presumably, a large proportion of your training attendees are electrical inspectors. With the understanding that some solar markets are more advanced than others and inspectors have varying levels of experience with PV, do you see the level of inspector knowledge keeping up with the PV industry?
JW: In the past, AHJs usually knew more about electrical installations than the electricians doing the installations. With all of the new technologies coming to market, this is no longer true. Advanced electrical technologies including PV, fuel cells and EVs require large numbers of expert plan reviewers looking at the designs and well-trained electrical inspectors. Current and expected budget restrictions indicate that these well-qualified people will be in short supply. Many jurisdictions with funding restrictions are hiring combination inspectors who may not have had the advanced training that PV technology requires. Electrical inspectors tend to be very busy, and only a small percentage of them actually attend PV trainings. More need to. In some jurisdictions with a high number of PV installations, the chief inspector or the building official may decide that their entire staff should devote a day to PV training. However, funding limitations are affecting the training of the inspector community.

SP: What is your level of involvement with Underwriters Laboratories (UL)?
JW: I am on the Underwriters Laboratories Standards Technical Panels for PV modules (1703), inverters (1741), racks (2703) and dc PV AFCIs (1699B). These standards, along with the requirements found in the NEC, have a direct impact on the design and development of PV equipment.

SP: What is your level of involvement with the Solar America Board for Codes and Standards (Solar ABCs)?
JW: Under the Solar ABCs program, I provide current information on the activities of the PV Industry Forum, chaired by Ward Bower, as we develop, coordinate and submit proposals to the National Fire Protection Association (NFPA) for the NEC. We follow these proposals, and the proposals of others, through the 3-year code cycle. In addition, I recently authored a white paper for the Solar ABCs that clarifies how the NEC addresses the grounding of PV systems. This paper is titled “Photovoltaic System Grounding” and will be published on the Solar ABCs website this summer.

In the testing arena, I recently worked with other Solar ABCs members to verify that a “ground fault blind spot” exists on most of the current generation central inverters listed to UL 1741, which can result in fire hazards. [For more information on this topic, see “The Bakersfield Fire,” February/ March 2011, SolarPro magazine, and “The Ground-Fault Protection Blind Spot: A Safety Concern for Larger Photovoltaic Systems in the United States,” authored by Bill Brooks and available online at]

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