Solar equipment grounding

[Sledge319]

We have seen a significant increase in applications for roof mounted solar systems and have been diligently working on improving our review process. One item I keep seeing, and have spent a lot of time researching, is the sizing of the equipment grounding conductor. It is very common for the contractor to use a 6AWG EGC on the roof and then after the junction box or invertor they reduce the size to an 8 or 10. The 6 is oversized for what is required but I believe they use it because it is the minimum size that does not require protection so they can run it without conduit. My concern is that by reducing the size along the path to the grounding electrode, you are possibly creating a "choke" point or an impedance. The NEC identifies when or how you can increase the size of an EGC but I cannot find anything allowing the size to be reduced.

 

[ActionDave]

The only requirement is for a minimum size EGC.

 

[jaggedben]

See 690.46, which refers back to 250.120(C). The reason for the 6awg size on the array is purely out of concern for physical damage, where the larger size is considered mechanically stronger. FWIW, most AHJs in my area don't enforce the 6awg requirement, regarding EGCs under rooftop panels as not subject to physical damage.

There have been a lot of wrong ideas about solar panels needing special grounding electrode conductors. Thankfully, since the 2017 NEC, the code making panel has recognized that these ideas are wrong and removed such requirements. Only an EGC is required. See 690.47.

 

[electrofelon]

. My concern is that by reducing the size along the path to the grounding electrode, you are possibly creating a "choke" point or an impedance.

Think about it: why would that even matter when you have a good conductor like copper (even if it is "small") connected to dirt which is not even a conductor?