Ever-increasing code complexity red tags some installations.

The first residential PV projects were installed in locations far from the long arm of the building code establishment. As a consequence, many of the early PV installers were not familiar with or held to the standards set by the National Electrical Code, the International Building Code (IBC) and local jurisdictions. As the PV industry has grown, so has the need for strict compliance with these codes. Today's PV installations often require multiple permits and inspections. Installation techniques and practices have evolved accordingly. In addition, many traditional ac electricians are entering the PV field and implementing electrical trade practices during installations.

The PV, building and electrical industries are constantly evolving as new equipment and methodologies are developed and released. Consequently, the governing codes are also constantly being updated to meet the requirements of their respective industries. This requires contractors to stay abreast of new information and requirements as they are released. Many new and sometimes some old issues about code compliance surface during PV system installation and inspection. To add to that difficulty, depending on the jurisdiction you work in, you may be held to current code cycles or sometimes to previous versions. This ultimately leads to confusion among contractors, PV installers, and enforcement and inspection officials, especially as these groups communicate with peers in other states and jurisdictions.

GENERAL CODE VIOLATIONS
The NEC is the guiding document for the electrical portion of PV installations. Some jurisdictions have specialty code requirements, but most are based on the NEC. While the NEC is considered the premier document guiding electrical installations, its acceptance and interpretation is determined by the AHJ, as outlined in Article 90.4.

Sloppy workmanship. One of the first requirements in the NEC appears in Article 110.12, which states, Electrical equipment shall be installed in a neat and workmanlike manner. While the Code does not and inspectors cannot define neat and workmanlike, they will know it when they see it. When work is neither neat nor workmanlike, it is a cue to inspectors to look even harder for additional Code violations. A National Electrical Installation Standard Standard for Good Workmanship in Electrical Contracting published by the National Electrical Contractors Association defines this requirement. (See Resources.)

Wire management is one critical issue to consider during installation. Since most PV modules come with factory installed quick connect plugs, it is not easy to use conduit to protect and manage the array wiring. The installer must properly support the wiring to prevent it from being damaged, especially where it could be exposed to physical harm. Jim Dunlop of Jim Dunlop Solar, and author of Photovoltaic Systems says, One of the areas that I think can use some improvement is in the management of the PV source circuit conductors. Most installers protect wiring from damage caused by roofing and racking. While rodents are not a widespread problem, some installers in the northeastern US also install guards along the array edges to discourage varmints from chewing on the wires and causing failures.

Not installed to listing. Another general NEC requirement is found in Article 110.3(B), which reads: ?Listed or labeled equipment shall be installed and used in accordance with any instructions included in the listing or labeling.? This covers a large number of considerations, from mechanical to electrical.

A common electrical mistake is to install an overcurrent protection device (OCPD), such as a circuit breaker or fuse, in a manner that violates the ampere rating specified by the inverter manufacturer. This can result in the conductors being inadequately protected or in nuisance tripping, which ultimately reduces energy production. While this problem may have been more prevalent in the early days of grid-direct installations, it still comes up today.

Improperly sized fuses or circuit breakers for PV source circuits present another issue. All PV modules come with a series fuse rating that should be used to determine the overcurrent protection size for the PV source circuits. It may be possible to use smaller fuses, but this generally does not benefit the installer. The bottom line is that the OCPD used to protect PV power circuits needs to be sized based on NEC Article 690.8, not based on what is on the truck that day.

Typically, most of the components used in a PV installation will be installed outdoors. This requires that individual components be listed for outdoor use and exposure to the elements. Many of the enclosures used, for example, will carry a National Electrical Manufacturers Association (NEMA) rating of at least 3R. This indicates that an enclosure is weather resistant when mounted in a vertical orientation. Most of these boxes are not considered weather resistant when mounted at any other angle. Therefore, using a NEMA 3R junction box or disconnect mounted parallel to a roof surface is a direct violation of Code, unless additional testing was performed by a Nationally Recognized Testing Laboratory (NRTL). It is possible to use a NEMA 4 enclosure where the location requires mounting the box on an incline or even on its back. Although several combiner box manufacturers use NEMA 4 enclosures, most disconnects must be mounted on a vertical surface.

Article 690.4(D), an addition to the 2008 NEC, requires that equipment used in PV systems, including sourcecircuit combiner boxes, shall be identified and listed for the application. This addition to Code restricts the use of on-site manufactured combiner boxes. While it is possible to individually purchase the components used in a listed combiner box, if these are assembled in the field the final product is not identified and listed for the application. This requires that a NRTL evaluate the product and components used. The NRTL verifies proper construction and checks that the accompanying documentation is sufficient for field personnel to properly install the unit.

PV combiner boxes now need to be listed to UL 1741. Installers can choose among several types of combiner boxes, from simple junction boxes to large multiple string combiners, that incorporate fusing. (See Pulling It All Together, April/May 2009, SolarPro magazine.) Article 690.4(D) should eliminate the use of non-listed combiners, but John Hardwick, training manager for Sharp Solar, notes: ?I am still seeing installations where the installer has used indoor-rated wire nuts inside a NEMA 3R junction box on the rooftop. We encourage installers in our trainings to use listed junction boxes that are properly flashed at the roof penetration to ensure a proper electrical connection and a weather-tight junction on the roof.

WIRING METHODS
PV systems present their own set of challenges when it comes to wiring. Source-circuit wiring is often exposed to sunlight and extreme temperatures, while output circuits are often run at very high dc voltages inside hot conduit. The inverter output circuit for utility interactive inverters sends electricity into the grid the wrong direction for current to flow, in the minds of many inspectors. Live dc circuits on the roof always cause inspectors grave concern, even though these are inherently current limited. These are all legitimate concerns that system designers and installers need to account for and be prepared to explain to permit and inspection officials.

Temperature correction. One of the first Code requirements that PV installers need to review is Article 110. This article specifically addresses temperature limitations associated with conductor ampacity. Since PV systems operate at excessive temperatures, this section can have major implications.

Article 310 in the 2008 NEC now includes Table 310.15(B) (2)(c), Ambient Temperature Adjustment for Conduits Exposed to Sunlight On or Above Rooftops. The adjustments in this table ?shall be added to the outdoor temperature to determine the applicable ambient temperature for application of the correction factors in Table 310.16 and Table 310.18. Such an adjustment can require significantly larger wire sizes, depending on the local temperatures and the height of the conduit off the roof.

According to Brian Crise, lead instructor at the Portland, Oregon, NECA/IBEW training facility: This is one of the areas that catches some traditional electricians. Many of them do not estimate rooftop temperatures as high as they can actually get.? Crise also sits on Code Making Panel number four, which includes purview of Article 690. One of [the panels big concerns, he explains, is equipment installed outside of its temperature range. This includes using properly rated conduit, wiring and enclosures. In addition to applying the new temperature adjustment table, installers also need to be aware of the temperature effects on the conduit. Both PVC and metallic conduit have large expansion coefficients when placed on rooftops. Therefore, the conduit runs need to be installed with expansion couplings and proper support.

Article 310.15(A)(2) includes an exception allowing for a less restrictive calculation. This exception applies where the conduit along the rooftop is less than 10 feet in length or less than 10% of the total circuit length, whichever is less. If the conduit is minimally exposed, the balance of the conduit length is able to dissipate the heat effectively, thereby reducing the heating impact. This exception may allow installers of residential PV to avoid upsizing conductors and conduit.

Color coding. A longstanding convention in PV installation is to mark the positive dc circuit conductor red and the negative conductor black. While this may be recognizable to PV professionals, it is not a correct method per the NEC nor is it safe. It may lead to confusion. Article 200.6(A) dictates that grounded current-carrying conductors smaller than 6 AWG ?shall be identified by a continuous white or gray outer finish or by three continuous white stripes on other than green insulation along its entire length. There is an exception to the size restraint in 200.6(A)(2). This allows PV source conductors to be installed and marked at their terminations. The use of white tape, for example, can identify a PV source conductor as grounded.

When describing and calling out conductors, it is more appropriate to refer to nongrounded current-carrying conductors and grounded current-carrying conductors. The former is typically the positive conductor, and the latter typically the negative. This is more descriptive and identifies the conductor?s role in the circuit to qualified personnel. Under this nomenclature, color coding is also clarified.

The nongrounded current-carrying conductor may be any color other than white, gray, green or green with yellow stripes. Typically, this conductor is red, which is acceptable per the NEC and stands out to a technician servicing the system. When a positively grounded PV system is employed, it may be in the installer?s best interest to use both proper color coding and additional labeling to identify the system as positively grounded.

Readily accessible conductors. NEC Article 690.31(B) allows for the installation of unprotected current-carrying conductors in PV systems. This is one of the only places in the NEC where such conductors are allowed. In the 2008 NEC, however, there is an addition to 690.31(A) that states: Where photovoltaic source and output circuits operating at maximum system voltages greater than 30 volts are installed in readily accessible locations, circuit conductors shall be installed in a raceway. This requirement is problematic for ground mounted or other PV arrays that are considered readily accessible per NEC Article 100 and use modules with the quick connect cables attached to the junction boxes. These modules do not have a method for conduit attachment and make it difficult to comply with this article.

The integrator is left with the dilemma of how to best install the system and comply with the NEC. The easy answer is to make the array not readily accessible, and this generally translates into build a fence. This is an additional expense, and it has a visual impact that the system owner may not want. Another method is to create a wiring chase that integrates with the racking system and renders the wires inaccessible. In this scenario, it is best to work closely with the AHJ to determine what it will accept.

Article 690.31(E) appeared in the 2005 NEC. This addition allows dc conductors from the PV array to run through a structure before being terminated at a readily accessible disconnect, as long as the conductors are located in metallic raceway. It is now generally accepted that metallic raceway includes conduits such as EMT and flexible metallic conduit but not metal clad cable, which is technically a cable assembly. The Article also includes language that refers specifically to utility interactive inverters, so depending on your AHJs interpretation, the method outlined in Article 690.31(E) may not be acceptable for off-grid installations.