Section 690.47: Grounding

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
NEC 690.47(D) has been a problem child since it was put in the NEC. There was never a reasonable reason for it and in 2017 it was made optional and is pretty much ignored now. But under the 2008 NEC it is mandatory.
Even when and where it was "mandatory" most PV integrators I knew ignored 690.47(D). I only encountered a single inspector who held our feet to the fire and made us install a ground rod for a roof mounted array. We appealed to his boss, who was much younger than him, and she told us that she agreed with us but she wasn't going to overrule him.
 

Carultch

Senior Member
Location
Massachusetts
The term "functionally grounded" was created because the PV industry is dead afraid of labeling DC PV conductors as ungrounded. If we pick it apart a functionally grounded system is an ungrounded DC system with a way to test the DC conductors to determine if any of them have become grounded and if they have then shut down the system. Remember the GFDI fuses in the neutral to ground bond that we said for years made a DC system solidly grounded? They are now considered a functionally grounded system.

That explains why they grouped two wildly different kinds of systems to both now classify as "functionally grounded".
 
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