Interpretation of NEC code / can of worms [RE-wrenches]

Joel Davidson joeldavidson at earthlink.net
Wed Sep 3 20:23:13 PDT 2003


In Los Angeles, inspectors want XHHW-2 in conduit for the DC high voltage wire runs.

Vince McClellan wrote:

> 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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