
I just had an inspection today by an inspector that has obviously been studying
NEC article 690,which was a refreshing difference from what I usually encounter.
However, he had  some very different interpretations of the code than any I've
heard so far, so I thought it would be a good thing to get some second opinions. 
On this installation I have #10 USE-2 wire coming down off of a roof mounted
array from 18 Sharp modules, through a weather head, and then junctioning to #10
thhn in a conduit body, then to a Sunny Boy inverter. The inspector wants me to
replace the thhn with a 90 deg. rated conductor all the way to the inverter, even
though the conductors are not in a high temperature location. He says because it
is part of the original circuit it has to be the same insulation rating through
out the whole circuit. Anybody know where I can find THAT in the NEC code?
The other issue that I have is most of the inspectors I'm working with want me to
install an additional grounding electrode with a #6 grounding electrode conductor
coming straight down from the array. It was my understanding that there should be
only one grounding electrode in a system. It states in the notes in the NEC
handbook in article 690.47 that "The ac and dc grounding electrode conductors
where both are present should connect to a common grounding electrode or
grounding electrode system.  
I remember back to some of the first Trace inverter manuals when the engineers
at Trace encouraged installers to ground to only one grounding electrode because
of the  of a potential voltage difference between two grounding
electrodes in the event that lightning strikes closer to one grounding electrode.
Their observation was that the voltage potential between two electrodes would of
course cause current flow through the system damaging sensitive electronics such
as inverters.
Anyone care to comment on any of this.

Vince McClellan
Energy Design 

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