Dave,
To add to your point, the typical way to wire an ungrounded PV system is to use modules with PV Wire-connect them to homeruns of PV Wire-then transition at some point to standard wire in raceways. This means that the only change from a wiring method point of view is to use PV Wire wherever you used to use USE-2 (like my multiple uses of USE in a sentence?-I think we have the basis for a new Dr. Seuss book). Now for my real bombshell-There are no ungrounded PV systems being installed in the U.S. today that I am aware of. But what about all those non-isolated "TL" inverter systems? The array cannot be grounded with a "TL" inverter because the system becomes grounded the moment it connects to the grid. So is it an ungrounded system or a grounded system. I could easily argue this both ways and be wrong and right at the same time. So what is an ungrounded PV system. A truly ungrounded PV system is one where neither the positive, nor the negative are referenced directly to earth. This is common in Europe for large inverters. The ground-fault detection is done by putting an insulation monitor on the array that runs 24/7. You can't put an insulation monitor on a non-isolated inverter system because it will trip the moment it connects to the grid. Last bombshell-All grid-connected PV systems currently being installed in the U.S. are not ungrounded and they are not solidly grounded. They are all actually employing an alternative to both grounded and ungrounded from 690.41-"shall use other methods that accomplish equivalent system protection in accordance with 250.4(A) and that utilize equipment listed and identified for the use " I really love the irony that my friends like John Wiles and others have been tooting the horn of grounded systems for so long, but our systems are not solidly grounded (because of the ground-fault fuse). The more-correct term for our systems is "functionally grounded", but even that does not fully cover it. I'm writing a document on this presently-I've never had so much fun with grounded in my life. Bill. From: [email protected] [mailto:[email protected]] On Behalf Of Dave Click Sent: Friday, June 28, 2013 11:04 AM To: [email protected] Subject: Re: [RE-wrenches] double insulated wire 690.35(D) does not require PV WIRE be used for the whole dc circuit. You can use either: (quoting directly from 2008) 1) Nonmetallic jacketed multiconductor cables 2) Conductors installed in raceways, or 3) Conductors listed and identified as PV WIRE installed as exposed, single conductors Similarly, I don't believe that the NEC requires red and black color coding, either, though it makes the most sense given convention. Note Brian Teitelbaum's 6/3 email about PV WIRE noting that "double-insulated" is a bit of a misnomer. Some PV WIRE is single-insulated. DKC On 2013/6/28 13:47, [email protected] wrote: In ungrounded systems the PV wire requirement is to be used the whole DC circuit, so that is all the way to the inverter. 690.35 (D) is pretty clear . Because it is ungrounded the protection is the PV wire's fire rating and you don't get that with thhn/thwn. And of course Red for positive and black for negative. Most building departments have not pick up on this yet. But they will. Aram
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