Module Grounding Clips and the NEC

Language in Article 690.43 of the 2008 NEC allows the use of new array grounding methods and hardware typically referred to as module grounding clips. The article states, “Devices identified and listed for bonding the metallic frames of PV modules shall be permitted to bond the exposed metallic frames of PV modules to the metallic frames of adjacent PV modules.” In addition, several module and rack manufacturers and system integrators have developed system kits that utilize grounding clips as well as lug sets to bond between mounting rails. What’s your take on this new language in the 2008 NEC? What are the implications for these grounding methods with regard to safety and the longterm integrity of these electrical bonding methods?

IEC 61730 Will Test and Document Module Grounding

John Wiles / Southwest Technology Development Institute / Las Cruses, NM / nmsu.edu/~tdi/

Article 110.3(B) of the National Electrical Code requires that the instructions and labels provided with a listed product be followed. PV modules are marked for grounding at specific points. Installation instructions specify grounding at the marked points and do not generally address grounding the module at mounting holes or at other locations.

A few manufacturers have published technical bulletins that show other grounding methods. These bulletins may or may not have been reviewed by UL where they differ from the listed grounding points. Also, even if reviewed, they may not be in compliance with all NEC requirements or might describe grounding techniques that have not withstood the test of time.

I have been making formal and informal inputs to UL for several years concerning module grounding and requiring manufacturers to tighten up documentation and procedures. In addition, I have been encouraging manufacturers to have their modules tested with new grounding products and to include this information in their instruction manuals. This way, the AHJs will not have any questions, and the installation will be code compliant.

The PV team at UL has stated that it is not sure that the UL grounding standard, UL 467, is suitable for evaluating devices and methods used for grounding PV modules. A UL task group, of which I am a member, is developing a change to the module standard UL 1703 (soon to be IEC 61730) that will test and evaluate new grounding devices with actual PV modules during the module listing process.

UL issued an interpretation of UL 1703 in August 2007 that says that manufacturers must specify, in the module instruction manual, the grounding method(s) and materials that must be used to establish the external field-made grounding connections. These methods and materials will be evaluated as part of the module listing process and will apply to all existing listed modules and their instructions as they come up for review. For example, any threaded connection used for grounding must be capable of being torqued and loosened 10 times without damage to the connecting parts. This requirement will probably end the practice of driving a thread cutting/thread forming screw into the module frame for grounding.

Finally, when using a new grounding method that does not result in an electrically continuous wire to each PV module, grounding continuity must be addressed. One of the oldest requirements in the Code is to make a grounding connection first and break it last (250.124(A)). Consider a module with an internal ground fault to the frame. If the circuit conductors are left connected, and the module is unbolted from the grounded rack—disconnecting the frame grounding first rather than last—the module frame may be energized with up to 600 volts to the grounded rack.

For the grounding method we currently use at the Southwest Technology Development Institute, see Appendix G in the latest version (1.6) of the PV/NEC Suggested Practices manual, available here: nmsu.edu/~tdi/Photovoltaics/Codes-Stds/Codes-Stds.html

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