In the early days of PV systems, modules had junction boxes to which conduit was attached. Module wiring was added by the installer and run in that conduit, which kept wires organized and protected. To reduce installation time, junction boxes have been replaced with pre-attached wire leads. The leads from one module plug into the connectors of the adjacent module. That change has brought with it the challenge of protecting and managing the wires dangling between the modules, as well as the exposed home-run wiring behind the array.
While the NEC does allow these conductors to be exposed, it is required that they be supported and secured for aesthetic and safety reasons. If the insulation on dangling wires comes into contact with sharp or abrasive edges of metallic racking or asphalt shingles, for example, it can become damaged over time.
Historically, wire ties have been used to keep conductors from laying on the roof, and organized and neatly secured to the rack. UV-resistant ties are durable and long-lasting, especially if kept out of direct sunlight. Even so, the ravages of weather and time will eventually take their toll on plastic UV-resistant wire ties, and they will need replacement.
Other bundling and securing solutions include metallic clamps with EDPM rubber collars; stainless steel cable clips, such as those from Wiley Electronics; and SunBundler vinyl-coated stainless steel cable ties from Heyco. Some rack manufacturers offer solutions with integrated wire management. Manufacturers offering integrated wire management for their pitched roof racking products include Legrand, Lumos Solar (see “Design with PV in Mind”), and SnapNrack.
Array wire management also should consider the potential for critters, such as squirrels that like to chew on these wires. Installers facing this problem have innovated with homebrew solutions to block critters but not airflow (such as wire mesh screens secured between the array edge and the roof), and a few companies now have developed products to address this issue as well, such as Heyco’s Sunscreen and Spiffy Solar’s galvanized steel screen and Spiffy clips.
While careful wire management can take some time, it is an important step in the installation process. Modern PV arrays can operate at up to 600 VDC and care must be taken to protect conductors from becoming damaged, since compromised conductors have the potential to create a ground fault, which can lead to rooftop fires.
While this article has focused on rooftop wire management, it is also important to understand the NEC 690.31(A) requirement for removing access to “PV circuits operating at maximum system voltages over 30 volts installed in readily accessible locations,” such as those on the back of ground-mounted (and shorter pole-mounted) arrays that either animals or humans can reach. This requirement is generally met by installing a fence around the back of the array or by routing wires through a wire chase attaching to the rack itself.