There doesn't seem to be a definitive and detailed consensus article/resource out there that addresses this topic. There are articles that dance around the subject, but little in terms of practical ways to accomplish grounding/binding with a supply side interconnection. AHJ's and engineers have all kinds of differing opinions. As an industry, it seems like we should have a definitive guide on the subject.
Let's take a simple/common ungrounded inverter (or microinverter) system that is interconnected using supply side taps inside an existing load center with main disconnect. From the roof to the PV AC Combiner you have an appropriately sized EGC, and no GEC because a GEC is not required in this ungrounded system other than the existing premises GEC (and GE system). Let's assume the AHJ agrees that no GEC is required from the roof, which is a whole other subject that drive me nuts). Coming from the PV AC Combiner panel (if present) or Inverter you have two current carrying conductors L1 and L2 that are tapped on the service conductors. The neutral from the PV AC Combiner or inverter is landed on the existing neutral bus of the same main load center where the tap is made. Now what happens with the EGC that comes from the roof to the PV AC Combiner (or inverter)? What I have run into, and there may be other opinions, are the following assertions by AHJs: - Land the EGC on the PV AC Combiner and stop there. Bond neutral to ground. The neutral carries the fault current to the system bonding point in the main service panel. - Land the EGC in the PV AC Combiner and continue the EGC to the ground bar in the main service panel. Do not bond neutral to ground in the PC AC Combiner. - From the PV AC Combiner, install a GEC directly to the existing grounding electrode, and do not run an EGC to the main service panel. - Some combination of the above. Can anyone point to a clear and concise 3-line diagram that explains the acceptable options? Hopefully something that and AHJ will consider, like an IAEI article or NEC Handbook graphic. Jason Szumlanski Florida Solar Desing Group
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