PV connectors play a crucial role in the wiring of solar arrays. As designed and if correctly installed, they provide a high-voltage, high-current, low-resistance DC connection in a housing that is water-tight, temperature-resilient, UV and wire-pull-resistive over the 25-year-plus life of the solar installation. In addition, their snap- together connection technology speeds installation of solar arrays. They are, however, often a source of array failures.
A study by the Fraunhofer Institute for Solar Energy Systems ISE of Freiburg, Germany, examined the causes of thermal failures of PV arrays and found that PV connectors and crimps were the largest single cause of DC wiring failures. Most of these failures occurred during the first five years of installation, leading researchers to suspect poor installation practices as a primary cause.
Discussions here in the United States with electrical inspectors have also yielded the following insights into PV connector failures:
- Poor contact crimps or crimps that have grabbed some of the wire insulation
- Contacts that were not installed correctly into the connector, causing high-resistance connections
- Water intrusion due to improperly assembled connectors
Several inspectors have also observed field installers crimping PV connectors’ contacts with pliers. Additional comments highlighted the “loose” fit of PV connectors of different manufacturers.
Compounding the array failures of PV connectors is that it can be difficult to see improper assembly and poor contact crimps. Connection failures are often hidden within a seemingly acceptable connector. Outside of a complete failure, such as a distorted or melted connector, visual detection is nearly impossible. Thermal imaging is often the only way to detect these problems. The energy loss, diagnostics and repair costs associated with hidden failures can be significant.
Sources of PV connector failures
PV connector failures can be categorized into two areas: incompatibility issues and connector wiring problems. Most of these failures are associated with field wiring. Factory-installed connectors found on the back of PV modules are usually not a significant source of problems. However, field-installed connectors such as those for home-run string end cabling used with string and other central inverters can be problematic.
Incompatibility issues are often caused by the mating of PV connectors from different manufacturers. While many connectors are considered “compatible,” there is no industry standard for a uniform connector design. Due to the differences in design tolerances, crimp tool requirements and contact and housing materials, optimal electrical connection cannot be guaranteed. In addition, while all PV connectors should be tested to UL 6703, this standard does not cover the mating of connectors from different manufacturers unless specifically tested — something rarely done. Some manufacturers caution against the mating of different connector brands, and the recommended practices should be followed.
Most PV connectors use crimp-style contacts. Whether factory- or field-installed, these connectors require the manufacturer-recommended crimp tool and proper assembly for a trouble-free installation. Crimp tool calibration requirements and crimp die limits must be adhered to for trouble-free installation over the lifetime of the array. New tool-less PV connectors are now available as well. These connectors eliminate the tooling and assembly requirement, but they use a temperature- and vibration-resistant spring contact for wire connections.
Best practices for PV connector installation
The solution to the challenges of PV connector failures is to ensure the correct installation during the initial wiring of the array. Some best practices that can be used to accomplish this are:
- Proper training of installers on PV connector assembly
- Use of the proper crimp tools, calibration and methods recommended by the PV connector manufacturer
- The use of tool-less spring contact PV connectors, eliminating the crimping requirements
Beyond the challenge of correct PV connector assembly is the issue of incompatible PV connector mating. Best practices in this area include always specifying the same brand of field connector as that supplied by the PV module manufacturer. This includes the use of microinverters and optimizers. Some of these manufacturers are making this easier in some cases by offering a choice of PV connector brands on their equipment.
The use of PV connectors from the same manufacturer, proper training, recommended crimp tools or the use of a tool-less spring contact PV connectors can help minimize the impact of connector failures.
Dan Sylawa is senior business development manager for Phoenix Contact.
— Solar Builder magazine