I am looking for a memory refresh here. What is the "summary of events" of the classification of the EGC of a transformerless inverter's output circuit. A couple years ago, we were installing some sunny tripowers, and the EGC terminal was labeled "EGC/GEC". Then I have memories of some authority or entity (UL?) clarifying that transformerless inverters do not have/require a GEC.
UL standards say that unless you have a grounded DC conductor, you don't need a grounding electrode conductor. Transformerless inverters can't have a grounded DC conductor so by UL they don't need a GEC. The same goes for other ungrounded inverters that might actually have a transformer (e.g. Enphase); strictly speaking what matters is whether you have a grounded DC conductor.
Despite UL, the 2014 NEC still has language requiring a GEC. (690.47) But the 2014 NEC allows this conductor to be sized to 250.122 (rather than 250.66 or 250.166). This basically makes it an EGC, size-wise, except that your AHJ might still enforce installation requirements like it being continuous (or irreversibly spliced), bonding bushings, etc. (i.e. 250.64 stuff).
The 2017 Code will dispense with
all that GEC stuff for all systems except those that actually have a
solidly grounded conductor. This will strip away any type of GEC requirement for all typical grid-tied systems and just require bonding (EGC). Systems with truly solidly grounded conductors would probably only be really basic old-school off-grid stuff with DC utilization. Everything else with modern inverters will just require an EGC to a (usually already existing) premises grounding electrode system.
Finally, could the requirements/lack of requirements for a GEC for transformerless systems be different or interpreted differently in the 2008 vs 2014?
Strictly speaking, the size of the GEC is the only clear difference in 2014 for ungrounded systems. There's also language about an AC equipment grounding system being permitted for inverter bonding and GDFI reference. This essentially means you don't have to run a GEC from/to the
inverter. But your AHJ could possibly still require a GEC from somewhere, such as from the array, especially if your AHJ wants to enforce the godawful 690.47(D).
If you're on the 2011 code or earlier you can be required to do the whole GEC shebang from pretty much wherever the AHJ wants. At any rate the inverter type doesn't matter one wit as far as those NEC cycles are concerned.
With that said, around here (2011 code) almost none of the AHJs I work with enforce the GEC requirements for transformerless inverters. (There's one who wants it from the array, but doesn't care about the inverter.) I think the reason this isn't enforced anymore is largely because Enphase put out a white paper arguing very strongly from the UL point of view, and most AHJs didn't want to argue with installers about such a large chunk of projects, so they went along with that view, and did so generally. Your mileage may vary widely in different parts of the country, but the biggest changes should come when your location gets on the 2017 NEC or equivalent.
