John Wiles works at the Southwest Technology Development Institute (SWTDI) at New Mexico State University. SWTDI provides engineering support to the PV industry and provides that industry, electrical contractors, electricians, and electrical inspectors with a focal point for Code issues related to PV systems. He serves as the secretary of the PV Industry Forum that submitted 55 proposals for the 2014 NEC. As an old solar pioneer, he lived for 16 years in a stand-alone PV-power home in suburbia with his wife, two dogs, and two cats—permitted and inspected, of course. The PV system on his retirement home is a 9 kW (ac) utility-interactive system with a full-house battery backup.
This work was supported by the United States Department of Energy under Contract DE-FC 36-05-G015149
Gray Areas in PV and the Code
The National Electrical Code, even though it is now almost 900 pages long, cannot specifically define every particular piece of equipment and every installation requirement for that equipment. There are always going to be areas that are left to the interpretation of the local inspector (the AHJ). This article will cover four gray areas that I get calls on and, perhaps, generate some discussion that may lead to clarifications.
Batteries in PV Systems
Electrical power outages are becoming more common in recent times with man-made and natural disasters, and the aging utility infrastructure. With natural disasters such as Hurricane Sandy, tornadoes, and other severe weather conditions, many people who are already using photovoltaic (PV) systems and many that do not have PV systems are going to be interested in utilizing PV systems in the event of electrical power outages. The electrical inspector can expect to see increasing numbers of battery-backed-up, utility-interactive photovoltaic power systems.
Unraveling the Mysterious 705.12(D) Load Side PV Connections
The requirements pertaining to the connection of utility-interactive photovoltaic (PV) power systems to the load side of the main service disconnecting means have been with us for years. In the earlier codes, the driver was 690.64(B) and now those requirements are found in 705.12(D).
PV Systems in Unusual Locations, To Inspect or Not?
In the normal workday, inspectors may drive pass numerous PV systems that are not located on a dwelling or a commercial building and are in somewhat obscure, out-of-the-way locations. When these systems are noticed, the question arises, Should they be permitted and inspected? Here are some examples of such systems.
Inspectors Rejoice! At Last — Significant Progress in a PV Standard
Most inspectors don’t have or have not read the UL Standards related to PV systems, because the standards are expensive and do not relate directly to the job of ensuring that listed PV modules and inverters are installed in a manner that meets the requirements of the National Electrical Code (NEC–NFPA 70). However, the requirements in the standards affect what the instruction manuals must say and those instructions guide the PV installer because NEC Section 110.3(B) requires that the instructions and labels on listed products must be followed.
The Conductors, Getting Solar Energy to the Inverter for 40–50 Years
PV modules may be generating energy for 40–50 years after installation. While power production may not be what it was when the PV system was new, hazardous amounts of voltage and current will be still available from the PV array. The rooftop, outdoor environment is harsh. Unlike HVAC equipment, which requires periodic inspections and maintenance, PV modules and the rooftop wiring and equipment may not be examined for the life of the system.
Microinverters and AC PV Modules Are Different Beasts
Microinverters and AC PV modules are becoming very common in residential and small commercial PV systems. They have even been used in PV systems rated at 60 kW and above. They have some common features. For example, microinverters and AC PV modules have similar ac output characteristics, connections and code requirements.
More Questions from Inspectors Numerous PV Systems Pose Issues
Photovoltaic (PV) systems prices continue to drop and inspectors are getting numerous requests for inspections. The questions that I receive indicate that this is new territory for many inspectors. These questions also indicate a few "holes” in the National Electrical Code, which we hope to plug in the 2014 NEC.
Questions from Inspectors — Inquiring Minds Need to Know
The following questions and answers result from some of the more common situations that many inspectors face throughout their working day when seeing a new PV installation or reviewing a set of plans for a PV system. The questions are simplified versions of questions I receive in e-mails and from questioned plan sets as well as sometimes long, involved phone calls.
Inspecting PV Systems
Photovoltaic (PV) power systems are becoming more numerous, larger and more complex. Inspectors and plan reviewers have limited time to deal with these new systems and still carry on the routine electrical system inspections that have been done for 100 years or more. I intend for this "Perspectives on PV” articles to provide you with information on the Code requirements for these systems and also give you information on how to make the plan reviews and inspections easier and faster.
Two Important Inspection Areas & One for the Plan Reviewers
Photovoltaic (PV) power systems have PV modules and PV arrays that will be producing dangerous amounts of voltage and current for the next 50 years or more. If the inverters in these systems do not fail or are maintained in operating condition, significant amounts of energy will be supplied to local loads and to the connected utility grid. There are two areas of PV systems that deserve the attention of inspectors to ensure the safety of the public over these very long periods of time. One is proper grounding of the PV array and the entire system and the other is ensuring that the ac output connections have been properly made to the existing premises wiring. Plan reviewers can look at conductor types with an eye to durability and longevity.A Critical Look at Load Side Utility-Interactive PV Inverter Connections 690.64(B) / 705.12(D)
The NEC in sections 705.12(D) / 690.64(B) allows utility-interactive photovoltaic inverters to be connected on the load side of the service disconnect. This requirement has been in theCodesince the late 1980s when PV Article 690 first appeared. Except for a slight change in 2008, the requirement has been largely unchanged. A critical examination of the requirement and how it can be applied as well as various proposals that have been rejected over the years may yield insights on what is needed in the future.Changes and Challenges
For nearly a century from about 1897 to 1997, premises wiring systems in residences and commercial buildings have largely been collections of passive conductors, disconnects and overcurrent devices. Certainly there have been incremental improvements in these systems and they can be quite complex with the addition of transformers, motor controllers, GFCIs and AFCIs, but much of that complexity is due to the connected loads that are not covered in inspections under the requirements of the National Electrical Code (NEC).What Hath the 2011 NEC Wrought for PV?
The 2011 National Electrical Code (NEC) has been published by the National Fire Protection Association (NFPA) and is now available from numerous sources. It was adopted by some jurisdictions automatically on 1 January 2011, and will be adopted throughout the country over the next three years or even longer in some areas that are slow to change.
MARCH-APRIL 2011Conductor Sizing and Overcurrent Device Ratings
Conductor sizes and overcurrent device ratings are critical to the safe, long-term operation of any electrical system, but are of particular importance in PV systems where the outdoor environment can be extreme and the PV modules will be sourcing current for 40 years or more.Utility Interconnections and Code Requirements
Inspectors and installers continue to puzzle over the requirements in Section 690.64 of the National Electrical Code (NEC) that apply to the connection of utility-interactive inverters to the premises wiring and finally to the utility. This article, using the simplified block diagram, will attempt to clarify some of those requirements. Please refer to previous Perspectives on PV articles over the last two years for more detailed information. Ungrounded Electrical Systems! Ungrounded photovoltaic (PV) systems? What is the world coming to?
Actually the United States is catching up to the rest of the world, which has, for the most part, been using ungrounded electrical systems for as long as the U. S. has been using grounded electrical systems. More than 100 years ago, the debate on grounded vs. ungrounded electrical systems began and the U. S. went grounded while many other countries went ungrounded. When we discuss grounded vs. ungrounded electrical systems, we are addressing whether one of the circuit conductors, like our ac neutral conductor, is grounded or not. Odds and Ends
In the course of daily business, I get some questions repeated many times. I try to address these areas of common and frequent interest in this series of articles, but there are always a few that need clarification or repeating. Connecting to Mother Earth
When buying real estate, conventional wisdom dictates the three most important elements are—Location, Location, and Location. Based on my twenty-six years of working with PV systems, including the school of hard knocks, I strongly feel that the three most important elements to long- and short-term PV safety are—Grounding, Grounding, and Grounding. The Microinverter and the AC PV Module
No discussion of PV systems would be complete without a look at the newest inverter technologies that the installer and inspector will face. These new technologies include the microinverter and the AC PV module. Supply-side PV Utility Connections
Many larger PV systems cannot meet the requirements for a load-side (of the service disconnect) connection to the premises wiring system and a supply-side connection must be considered. Making the AC Utility Connection
Connecting the utility-interactive inverter to the utility grid properly is critical to the safe, long-term, and reliable operation of the entire system. The ac output circuit requirements and the circuits that carry the inverter current in the premises wiring are somewhat complex. However, meetingCoderequirements can and should be accomplished to ensure a safe and durable system.Connecting the Inverter
Connecting the utility-interactive inverter properly is critical to the safe, long-term and reliable operation of the entire system. Proper grounding of the inverter will minimize the possibility of electrical shocks and damage from surge currents. Understanding and applying the requirements of NEC 690.47 to the inverter grounding connections is somewhat complex but ensures that the user will be safe and that the inverter and other equipment will suffer minimum damage under surge conditions. Transfer Equipment Used in Optional Standby Systems for Commercial Applications, Part II – Transfer Equipment Options
The primary purpose of transfer equipment is to allow power transfer from a normal (Utility) source to an alternate (Generator) source while preventing the inadvertent interconnection of the normal and alternate source of supply during operation of the transfer equipment. During Part I of this series, we covered the fundamentals of transfer equipment used in optional standby systems and the use of key interlocks to provide a safe, simple, and reliable means of transfer. This article will explore transfer equipment options and provide additional guidance, questions to ask, and considerations for those systems.Approaching the Inverter
In our top-to-bottom perspective of a photovoltaic (PV) system, we are still on the dc circuits from the PV array and are approaching the inverter. There are always a few details that get overlooked in designing, installing and inspecting these systems. Still on the Roof
In our top-to-bottom perspective of a PV system, we need to look at one more component usually located on the roof. This is the PV source-circuit combiner and it will be followed in the dc circuit by the PV dc disconnecting means. PV Math
As we look at the PV array in a PV system, we find that many installers and inspectors are confused by the new system voltage calculations that may be required by the Code specific to PV systems. Code fine print notes (FPN) also address voltage drop that may be applied to the dc wiring from the array to the inverter. This article will cover both of those subjects.A Top to Bottom Perspective on a PV System
Photovoltaic power systems can be examined in a number of different ways as we have done in the last few years in the "Perspectives on PV” series of articles. In this article and the next few articles in the series, let’s start at the modules at the "top” of the system and progress through the system to the grid interconnection at the "bottom.” A utility-interactive PV system is a series-connected system, so where we start is not important and if you are in a hurry for information on some part of the system that we have not gotten to, you can review past articles in the series that are archived on my web site. Are We Grounded Yet?
Photovoltaic (PV) systems will be producing hazardous voltages and currents for 50 years or more. Over that period of time, they may or may not be operational and they may or may not be maintained. Proper grounding of all exposed metal surfaces in the system that may be energized by internal faults, poor terminations or failing conductor insulation is one of the most important requirements in a code-compliant system. Even in a failing or failed system, maintaining all metal surfaces at ground (or earth) potential will minimize the possibility of electrical shocks. Those grounding connections must be maintained in a harsh outdoor environment where they are exposed to heat and cold, solar radiation (ultraviolet radiation and added heat), dirt, rain, wind, ice, sleet, and snow. Grid Interconnections – Then  and Now 
The final connection between the photovoltaic (PV) power system and the electrical utility grid is always an area of high interest to both inspectors and to the utility, because both agencies are responsible for safety. These connections vary significantly from PV system to system due to the size of the PV system and to the configuration of the existing service-entrance equipment. These variations are made more complex because of differences in Section 690.64 in the National Electrical Code (NEC) between the 2005 and 2008 editions.Questions from the AHJ – To Fuse or Not to Fuse?
Nearly everyone agrees that the National Electrical Code gets better with every edition. However, new technologies like photovoltaic (PV) power systems and fuel cells are still evolving with new equipment, new wiring procedures, and new installation requirements being developed every week. With new inspectors and new installers coming into the field every day, questions are bound to arise. The question addressed below is very common and is frequently posed by both oldtimers and newcomers. The answer is not directly found in the Code but must be evaluated on a case-by-case basis by examining the system. Common PV Code Violations
As we move into 2008, the PV industry continues to grow by leaps and bounds. New module and inverter manufacturers are entering the industry, and the number of individuals and organizations installing PV systems is growing right along with the demand. Numerous small 2 kW residential and large megawatt commercial PV systems are being installed in many states, and all need to be inspected for code-compliance. With new people entering the industry every day, the common code violations we have seen in the past will continue. Here are some of the most prominent ones that have been repeatedly observed throughout the country. Ground-Fault Protection for PV Systems
Once upon a time (the 1987 Code cycle) in the land of Quincy, a group of alchemists from a national laboratory was elaborating on the excellence of their photovoltaic (PV) test facility in the distant Land of Enchantment. They showed some senior firefighters a picture of a burned PV module that had been subject to a ground fault and had subsequently melted down. The alchemists failed to mention at the time that this was a prototype, unlisted PV module, that the module was on a concrete pad, and that ground faults in PV systems were somewhat rare. These firefighting pros said to themselves, "PV ground faults lead to fires. Fires on the roofs and in the attics of dwellings are very hard to fight.” They then told the PV industry to propose Section 690.5 for the 1987 NEC to require a ground-fault protection device (GFPD). The proposal was accepted and the requirement was established, but no hardware existed.Why Inspect PV Systems?
Photovoltaic power systems are a rapidly growing (30+ percent/year) segment of the residential and commercial electrical systems market. These systems operate up to 600 volts and, in the larger commercial systems, the dc and ac currents can range up to 1000 amps. These levels of voltage and current, if not properly managed, pose both shock and fire hazards. The electrical inspection is a key element to minimizing these potential hazards. The Nature of the PV Module: Limited Currents Have Benefits and Drawbacks
The currents in a PV system are somewhat different from the currents traveling through a typical alternating current (ac) electrical system. Yes, the PV system has ac circuits and they are somewhat like a typical ac load circuit, but the direct current (dc) circuits are a little unusual. This article will address the unique aspects of these dc currents and how the Code handles them. Continuous Currents through Curious Cables
When inspectors see a photovoltaic (PV) power system for the first time, they will usually be faced with a type of wiring method not normally seen in residential or commercial electrical systems. That wiring method is the use of single-conductor exposed cables to connect the individual PV modules together in the PV array and is permitted by NEC 690.31. Exposed, single-conductor wiring is usually seen only in older neighborhoods as aerial feeders between buildings and in obsolete (but still with us) knob-and-tube wiring systems.Disconnect, Disconnect, Where For Art Thou?
The requirements and necessity for, and the location of disconnects in a photovoltaic (PV) power system are always of great interest. While PV equipment manufacturers, designers, installers, and electrical inspectors are all interested in getting safe PV systems, there are usually some "friendly” discussions on the whys and hows of disconnects needed to achieve those ends. The following information may shed a little light on those sometimes elusive disconnect requirements and how they can be addressed. The Development of Codes, Standards, and PV Equipment. How are they related?
PV equipment, safety standards, and electrical codes are not developed in a vacuum. How are PV equipment, PV standards, and PV codes related and how are they developed? Yes, there is a little "chicken or egg” in the process since the development of all three is an interactive process. Inspectors Demand More Answers
Electrical inspectors and other inspectors are curious people and when faced with reviewing plans for a PV system or inspecting such a system, there are many new features that are worth questioning. Here are some of the questions that inspectors have raised via e-mail, telephone calls, and during my PV/NEC presentations over the last four months. PV Systems and Workmanship
With electrical systems lifetimes exceeding forty years, PV systems must be installed using the best available workmanship to ensure public safety over the life of the system. Article 110, Requirements for Electrical Installations, and particularly Section 110.12, Mechanical Execution of Work, of the National Electrical Code (NEC) establish some general requirements for the installation of electrical equipment. A fine print note (FPN) to Section 110.12 references the National Electrical Contractors Association standard ANSI/NECA 1-2000 (latest edition is 2006) as describing accepted industry practices for electrical installations. This article will illustrate some areas that need attention when the workmanship of PV installations is being inspected. Of course, the local authority having jurisdiction (AHJ) determines what is acceptable. Penetrating PV Questions from Inspectors
Based on this series of articles and presentations that I make to groups of inspectors around the country, I get several calls and e-mails a week and sometimes several calls a day from inspectors looking at PV plans or inspecting PV systems. The questions that they pose are always challenging because most of the inspectors have done their homework and found the Code lacking in clear concise answers. I usually gain new insights on the Code from these calls. Here are some of the more common questions and the best answers that I have. I encourage these calls so that everyone involved can help to ensure that the numerous PV systems being installed are as safe as possible.Achieving The Art of The Possible
Those who have been following this series of articles for the last year or so may wonder what is involved in designing and installing a code-compliant, durable, reliable, and cost-effective PV system. Utility-interactive photovoltaic (PV) power systems are a mature technology. PV modules have warranties to 25 years and are predicted to produce significant amounts of power for 30 years or more. Inverters have warranties to 10 years and estimated life spans of 15 years or more with even greater longevity predicted in the future. PV systems can be designed and installed following existing guidelines and codes that will achieve long life, durable service, excellent safety, and cost effective power production. However, it is evident that great numbers of systems being installed today will not achieve the art of the possible because of poor design and installation practices. This article will address some of the steps that the PV systems vendor/designer/installer must accomplish to achieve a safe, durable, reliable, and cost-effective system. The 15-minute PV System Inspection. Can You? Should You?
As I make presentations on photovoltaic power systems and the National Electrical Code around the country, I frequently talk to inspectors who have as little as 15 minutes to make a residential electrical inspection. A common question is, "Can I inspect a residential PV system in 15 minutes?” This article will examine that question and also take up the question, "Should only 15 minutes be allocated for inspecting a residential PV system?”PV Plan Check
Electrical inspectors and electrical permitting personnel are seeing increasing numbers of photovoltaic (PV) power systems, both at the permitting stage and at the initial inspection. Both processes go much more smoothly for all concerned when the electrical system is properly documented. Since the typical PV installer has not installed hundreds of the same PV system, and the inspector has not seen hundreds of these systems, the documentation for these systems must, by necessity, be somewhat more detailed than the documentation associated with a typical residential electrical system. This article will examine a typical residential, utility-interactive PV system in terms of a package that should be submitted by the installer when applying for a permit or discussing the system with the inspector prior to installation. Installers can use this material to develop the package.Back to the Grid, Designing PV Systems for Code Compliance
In the September/October 2005 issue of IAEI News, the "Perspectives on PV” article discussed making the utility connection for utility-interactive PV systems. In some of the larger residential PV systems and in many commercial PV systems, the grid connection must be made on the supply side of the service disconnect to comply with the requirements of NEC 690.64. In designing PV systems for code compliance, knowledge of all of the various Code requirements is a must. This article will cover some of these requirements as they apply to a supply-side tap of the service-entrance conductors. PV systems employing supply-side connections should be inspected with these requirements in mind. Neither Sleet nor Snow nor Rain nor the Dark of Night…
Well, not exactly. Yes, all of those things will usually keep a system uses sunlight for fuel. However, these and other weather conditions also affect how a PV system is designed and installed to comply with the requirements of the National Electrical Code. With a PV power system lifetime exceeding 40 years, Mother Nature is going to use every trick in the book to make that system fail before its time. PV designers, installers, and inspectors need to devote significant attention to the weather-related safety requirements for PV systems to help ensure long-lived, hazard-free electrical installations.Making the Utility Connection
More than 90 percent of the new PV systems being installed throughout the United States are connected to the local utility with utility-interactive inverters (figure 1). These inverters range in size from about 250 watts (rated ac output) to about 250 kW. Multiple inverters may be used at a single location to provide even higher outputs. The connection requirements to the utility are established in various sections of the Code. Unfortunately, in many cases, these requirements are not fully understood or complied with. This article will concentrate on the requirements of the 2005 National Electrical Code Section 690.64, Point of Connection.Updates: Grounding PV Systems and Fine Stranded Conductors
In the "Perspectives on PV” article in the September-October 2004 issue of the IAEI News, the subject of grounding PV systems was covered in some detail. In the March-April 2005, IAEI News, we discussed the changes to Article 690 that appear in the 2005 National Electrical Code. As normally happens over the three-year code development cycle, new thoughts and ideas come to the forefront about how things should be done. Here are some of those thoughts as they apply to grounding smaller PV systems with single inverters sized below about 10 kW. Figure 1 shows the dc grounding for a PV system as spelled out in Section 690.47 of NEC-2005 and as described in the above-mentioned article. Permitting or Inspecting a PV System?
Inspectors are more and more frequently faced with permitting or inspecting PV systems as these systems proliferate throughout the country due to increasing regional financial incentive programs. Photovoltaic power is a relatively young technology and industry. While well-qualified people are installing many excellent, code-compliant PV systems, others are designing and installing these systems with little or no prior experience with electrical systems. Unfortunately, as financial incentives continue and even increase, more unqualified people are installing these systems. The electrical inspector, through the permitting and inspection process, can help the PV industry focus on the design and installation of safe, code-compliant PV systems. Inspector involvement early in the process often proves beneficial to all. Photovoltaic Power Systems and 2005 NEC
The 2005 NEC has been published and Article 690 has some changes that will benefit the Photovoltaic (PV) Power Industry and electrical inspectors by making the Code easier to understand and by allowing modified installation procedures. As jurisdictions adopt the Code (some as early as January 1, 2005—others possibly not for years), the new requirements may be applied. These requirements and other significant changes will be covered in this article.Do You Know Where Your Cables Are Tonight?
The use of fine stranded, flexible cables appears to be increasing each year. This is particularly true with relatively "young” industries like the photovoltaic (PV) industry, the fuel cell industry, and the uninterruptible power supply (UPS) industries. In many cases, technicians and installers in these fields prefer to use fine-stranded flexible cables in the larger sizes (1/0 AWG and up) due to the perceived easier installation of these cables.Stalking the Elusive and Somewhat Strange PV System
Even as PV sales and installations are booming (especially in states or regions providing financial incentives), PV systems are still relatively rare. While many inspectors have neither seen nor inspected one, some inspectors are inundated with inspection requests for these systems. Some inspectors never want to see or inspect a PV system. The rarity of PV systems does not prepare the typical inspector when he or she comes upon one for the first time. These systems and the equipment used in them are unlike other common electrical power systems. Should They Be Grounded?
At first glance, the obvious answer is: Photovoltaic (PV) systems are no different from other electrical power systems, and of course they should be grounded as required by the National Electrical Code. The real question is: How critical is grounding PV systems? Single Conductor Exposed Cables! Not In My Jurisdiction!
So sayeth the inspector when faced with inspecting his or her first rooftop residential or commercial PV installation. Yes, PV systems have some unusual wiring methods allowed by the Code. However, since all of the usual wiring methods found in chapter 3 of the Code also apply, the inspector must sort through what is allowed and what has been installed by the typical do-it-yourselfer or other uninformed installer of electrical equipment. Business will be as usual, with only a few small twists to learn.What Changed in Article 690?
Article 690, Solar Photovoltaic Power Systems, has been in the National Electrical Code (NEC) since 1984. An NFPA-appointed Task Group for Article 690 proposed changes to Article 690 for both the 1996 and 1999 codes. The Task Group, supported by more than 50 professionals from throughout the photovoltaic (PV) industry, met seven times during the 1999 code cycle to integrate the needs of the industry with the needs of electrical inspectors, and end users to ensure the safety of PV systems. The Task Group proposed 57 changes to Article 690 and all the changes were accepted in the review process. Photovoltaic Power Systems and the NEC
Photovoltaic (PV) systems that generate electricity from sunlight are being installed in ever increasing numbers throughout the United States and the rest of the world. Over 150 megawatts of PV modules are being produced worldwide annually and these PV modules, when exposed to sunlight, will be generating electricity for the next thirty years and longer. Utility-interactive PV systems (that can feed power to the electrical utility grid) and stand-alone PV systems are being installed in both rural and urban locations on residential dwellings and commercial buildings.