The National Electrical Code (NEC) requires grounding—bonding to an earth ground through a continuous electrical path—for any piece of exposed metal that could become energized from an electrical fault. PV array racks can include many metal parts, ranging from module frames and rails to conduit, that need to be bonded. (The terms bonding and grounding are used interchangeably to mean joining metal parts to form an electrically conductive path.)
Traditionally, modules and racks have been grounded with lugs, screws, bolts, or clips attached to every module frame and to each piece of rack that might come into contact with an energized conductor—which are then connected to ground via a copper conductor. Dissimilar metals in contact with each other, such as copper conductors and aluminum module frames, will result in galvanic corrosion, reducing the effective path to ground—so stainless steel and tinned copper hardware are used for grounding. Copper conductors are costly, as is grounding hardware, and together they are time-consuming to install properly. PV system equipment grounding has been a source of much frustration, sometimes resulting in improper installation and ineffective grounding.
A new standard, Underwriters Laboratories UL2703, is sweeping through the rack industry. NEC 690.43(E) states that PV mounting systems used to ground modules must be identified for that purpose. A rack listed to UL2703 standards could meet this Code requirement. UL2703-listed racks either use piercing teeth embedded in the module clips or other module mounting hardware (like serrated nuts) to cut through the module frame’s anodized coating, bonding the modules to the rack. The rack itself is electrically bonded through the hardware used to connect the individual rack pieces, so no extra grounding hardware is required. However, if a specific module hasn’t been identified and listed for bonding with a specific rack, then additional module bonding may be required.
PanelClaw, S-5!’s PV Kit, Schletter, SunLink, Unirac, and Zep Solar (along with others) have mounting systems that carry the UL2703 listing. To determine if a rack is listed to UL2703, and if that listing covers a specific module’s bonding, contact the rack manufacturer and the listing agency, and consult with the local authority having jurisdiction. If both modules and rack are listed, the installer needs to attach only one equipment grounding conductor to one point on each set of racks to provide a path to ground, and can forego other grounding hardware. Modules without metal frames do not need to be grounded, and neither do nonmetallic rack components such as plastic ballast trays.
The International Code Council (ICC)’s Acceptance Criteria 428 standard for PV systems provides an alternative to stamped engineered diagrams that jurisdictions can use to verify that a particular rack meets structural design requirements. ICC certification can help accelerate and lower the cost of the permitting process, as well as provide installers with a third–party verification that the rack is engineered to the standard. Unirac’s SolarMount (E)volution is the first ICC-certified PV rack on the market.