Also required is a listing for the “maximum rated output current of the charge controller (if installed).” Where applicable, this value is can be found in the charge controller manufacturer’s specifications.
Articles 690 and 705 require additional labels, such as the one required in Section 690.56(B), which specifies “a permanent plaque or directory providing the location of the service disconnecting means and the photovoltaic system disconnecting means, if not located at the same location.” This isn’t so much a label as it is a map. Two directory labels may be needed to identify the locations of the disconnecting means for both the PV system and the service.
Label material and attachment. The 2008 and 2011 NEC require permanent labels—many installers use plastic or metal engraved signs. When plastic is used, it should not be placed in direct sunlight, unless the plastic is specifically manufactured as sunlight-resistant. Where a label is installed in direct sunlight, a metallic engraved sign is generally more appropriate.
The most accepted practice is to install labels with an adhesive that is rated for outdoor locations and high temperatures. These labels generally meet Code requirements and are often acceptable for residential applications, depending on the AHJ’s Code interpretations.
Grounding PV systems is a complex problem for installers and inspectors alike. The difference in grounding requirements imposed from one jurisdiction to the next can make it difficult for installers to keep their methods consistent. In addition, the requirements for equipment grounding and system grounding are separate and need to be evaluated separately.
Equipment grounding. PV modules and associated racks aside, equipment grounding is generally the least divisive of all of the grounding subjects. The NEC is very clear: “Exposed non–current-carrying metal parts of module frames, equipment, and conductor enclosures shall be grounded…regardless of voltage.” For equipment and conductor enclosures, this is straightforward: A grounding conductor is used to bond all pieces of equipment to keep them all at the same electrical potential.
Unfortunately, using an equipment-grounding conductor (EGC) to bond PV modules and racks has never been simple or straightforward. While module manufacturers provide a location on their frames for the bonding hardware, that location is generally midway along the bottom of the frame’s long edge. This is not the most convenient place, especially if the modules are mounted parallel to a roof with minimal clearance. Additionally, the approved method of attaching the bonding hardware is not always well documented, and the appropriate hardware is not always included.
For bonding the racks to the EGC, installers have had to develop techniques without much guidance from manufacturers, and some poor choices were made in the past. One method used short lengths of THHN wire with ring terminals attached to each end. The ring terminals were then attached to the module frames via a self-tapping screw, which did not provide the proper electrical contact with the PV frame. The grounding method subsequently accepted industry-wide is to attach a tinned copper lay-in lug to each module and rack member, with an appropriately sized conductor bonding each of the modules and racks together. When installed correctly, this method is undoubtedly superior to many of the methods outlined in some manufacturer installation instructions.
Recently, some PV manufacturers have specifically mentioned this method of grounding in their installation instructions, which is good news for the PV installation community. The tinned copper lay-in lugs used for this purpose eliminate the deteriorating effect of dissimilar metals (copper and aluminum) in contact with each other. These lugs come standard with a stainless-steel set screw and are rated for direct burial. There is a similar-looking lug on the market that is made from aluminum and is not outdoor-rated; this product does not include a stainless-steel set screw and is not appropriate for bonding PV modules.