The Solar America Board for Codes and Standards (Solar ABCs) has released a final report, “Grounding Photovoltaic Modules: Issues and Recommendations,” which draws on feedback from solar industry experts as well as ongoing research at Underwriters Laboratories, Inc. (UL) and presents the issues with recommendations for changes to existing standards. The need for this study was identified through a gap analysis completed by the Solar ABCs following a survey of U.S. stakeholders.
There are two fundamental solar module grounding issues discussed in the report. The first issue is that there are limited numbers of approved (listed) grounding methods, despite a variety of installation methods and components available for grounding solar module frames. The report discusses the current development activities on three UL standards that will clarify the listing issue for dedicated photovoltaic system module frame grounding components.
The second issue discussed in the report is the lack of confidence in existing approved grounding methods due largely to failures observed in the field. These failures are often the result of loss of mechanical integrity, installation error, or damage from corrosion. The report includes results of a recent UL study on accelerated aging tests of solar module grounding connections in which different types of photovoltaic system grounding connectors were installed and tested in environmental chambers using both continuous damp heat and salt mist exposure.
“The Solar ABCs commissioned this work with the intent of providing the PV industry with practical guidelines and procedures for module grounding,” said Larry Sherwood, Solar ABCs Project Administrator, “The objective of the overall grounding PV module study is to make recommendations for an integrated set of tests and procedures that can be incorporated into the standards governing the grounding of photovoltaic system components.”
The results of the current tests described in this report reinforce the conclusions of a UL 1703 Standards Technical Panel (STP) subcommittee charged with developing new language for the Bonding and Grounding section. These tests combined existing low current tests with tests derived from UL 467 that are designed to ensure proper operation of overcurrent protection devices.
In addition, this report considers personnel safety and explores various fault scenarios in conjunction with International Electrotechnical Commission data describing body impedances and harmful levels of current to provide generalized methods of evaluating ground resistance limits. It also discusses more generalized design criteria using National Electrical Code principles. From a listing standpoint, the current test regimes recommended here should adequately address safety issues such as touch safe voltages and currents.
The standards are still undergoing significant change, so this report concludes with general recommendations for ensuring proper grounds based on field experience and feedback received throughout the course of this study. These recommendations include:
• Complete the proposed changes to the existing standards to improve the method and quality of ground connections.
• Elicit additional industry feedback from the accelerated aging test study to determine if and how these or similar tests might be incorporated into standard testing.
• Be aware of and make use of the new and expanded set of channels for listing module grounding equipment.
• Be aware of the principles of module frame grounding, the type of faults that may occur, and the implications for safety and ground system design.
• Follow the specific design and installation recommendations enumerated in this report, such as using proper materials and components, following manufacturer instructions, using torque wrenches to ensure proper tightening of connections, and avoiding connections of dissimilar metals that lead to corrosion, among others.
Download the full report: www.solarabcs.org/grounding