Cross-mating, which refers to the plugging of connectors from different manufacturers (between modules to optimizers/microinverters, modules to field-connectors, optimizers to field connectors or field connectors to the BOS system) is one of the most common PV wiring mistakes. In fact, the EU-funded Solar Bankability Project’s Failure Modes and Effects Analysis (FMEA), which sourced data from over 1 million documented insurance claims, showed that “different kinds of connectors” (cross-mating) had the highest risk potential in PV installations, and it wasn’t even close.
The reason for the risk here is connectors from different manufacturers have different dimensions, materials and engineering tolerance. The slight variation between different manufacturers can result in higher contact resistance (heat), water intrusion or unexpected deterioration of contact or plastic parts.
“Each connector has different critical dimensions and even using the most precise calipers to copy connectors still doesn’t guarantee a secure connection,” says Dean Solon, CEO and founder of Shoals. “Secondly, these connector manufacturers do not always utilize the same metals or procure their contact terminals from the same vendor. As a result, mixing dissimilar metals will unquestionably lead to thermal events [read: fires]. Pre-fabricators or field installers should use the opposite polarity from the same connector manufacturer used on the module datasheet. If it is not explicitly stated what type of connectors are being used on the module datasheet, reach out to the module manufacturer to identify.”
UL1703/6703, IEC 62548 and IEC 62852 (EN50521) testing does not allow for cross-mating. The good news is this is an easy problem to avoid during project planning. When designing or purchasing modules, field-connectors, inverter and optimizers and BOS systems, one needs to make sure that all connectors are coming from the same manufacturer. If you are using connectors labeled “MC4 compatible,” be sure to obtain a written statement from both manufacturers.
One of the most common issues in solar installations occurs when wire management is seen as an optional expense or somewhere to save on installation costs.
“The long-term system and maintenance costs that result from poor wire management practices far outweigh the effort required to implement a proper solution,” notes Sarah Parsons, Wiley product manager at Burndy. “Supporting PV wires at required intervals with listed solutions made from environmentally rated materials [such as stainless steel or UV-rated polymer] is the only way to align the lifetime of the wires with the intended system lifespan.”
This goes for the cables too. Jeff Wang, business development alternative energies – North America for Stäubli Electrical Connectors, recommends using only black XLPE cables and tin-plated copper cables.
“Color cables don’t survive the UV for the lifetime of PV system,” he says. “Incorporating carbon black in polyolefines greatly increases the UV resistance, and carbon black acts as UV absorbent and screens the polyolefine from the damage of UV lights. Bare copper starts to react violently with oxygen when temperatures reache 90 degrees. It forms copper oxide and greatly reduces the current carrying capacity of the wire. In outdoor environments where there is humidity and high temperature, tin-plated wire is the sure choice.”
3. Misapplication of components
Similar to No. 1, but more specifically: Understand the details of securing wire safely or choose a fastener that is tolerant of a wide variety of installation methods. For example, when putting metal-coated or plastic ties through sharp module mounting holes. With low-cost plastic ties, you should know exactly what you are getting as a system designer, which is a solution that could last as little as a few months. A metal coated product can lead to far greater damage than just product failure, like wire damage.
“In choosing a particular material or type of wire management component, metal tends to be more forgiving to install but less forgiving to the cable if installed improperly,” says Nick Korth with HellermannTyton. “Plastic wire management runs the opposite, requiring more care to design and install but is ultimately kinder on cable insulation. These considerations are an important part of your wire management strategy to ensure a long-term solar installation.”
Heyco sees a lot of installations where side-to-side cable retention cannot be achieved simply because of the mechanics of the part being used. For example, a standard cable tie is only going to provide so much side-to-side cable retention before it begins to sag throughout the array. Most PV module clips come with a unique spring retention tab that accommodates a variety of wire diameters while still providing side-to-side retention on the cable.
In large-scale applications, trends of higher voltages and the use of more string inverters out in the field call for a complementary update in wire management.
“Solar installations are now carrying energy as high as 1,500 volts with current approaching 1,000 amps, and it is critical for life safety issues to properly house the power cables to ensure a safe working environment for the solar technicians,” says Roger Jette, president of Snake Tray. “With more inverters in use, AC and DC cables need to be carried through a cable management infrastructure versus using hooks.”
4. Not planning for landscape
Module manufacturers are designing positive and negative leads anticipating they will be installed in portrait, though most rooftop installations are in landscape. Some 72-cell modules are manufactured with leads that do not reach adjacent modules in landscape, making it impossible to string a row together.
“These short leads force installers to wire in columns on a landscape rooftop system,” says Jonah Coles, product solutions manager with Ecolibrium Solar. “In this situation, choose a racking system with built-in features to secure wires across the inter-row space. This will make stringing columns as easy as stringing rows.”
Another challenge is that dual junction boxes with a short lead on each side of the module are becoming more prevalent. This makes wiring especially challenging when using optimizers and microinverters because both leads need to be brought to the optimizer or microinverter, which also makes wiring in landscape more difficult.
“Consider these factors when choosing modules. Make a string map to organize the wiring path based on the module you are using,” Coles says. “Then choose a racking system with flexible wiring options and have your racking solution quoted to include wire clips. These planning tips will avoid delays by providing installers with a solid plan and the appropriate material to get the job done.”
— Solar Builder magazine