Mark,
The ac side of the system is clearly NOT separately derived since the neutral ground reference is not derived at the inverter but at the service entrance. Your previous post is correct about the fact that, since we are not pulling dc loads off the dc side, it really is not being used as a separately derived system in the traditional sense of the word. We have no provision in article 690 for this specific arrangement. If you have a good suggestion for a provision in 690, with a good substantiation, we might be able to do something with it on the Code Making Panel. I think what we have in the 2011 NEC will work for most cases. You are correct that an ungrounded dc PV system does not require a GEC. It does require an EGC for the metal parts, of course. The reason I'm not that interested in fixing stuff on the grounded side is because I don't believe in grounded dc systems operating above 100V anyway. We need to get manufacturers to move to inverters and equipment that is setup for ungrounded systems sooner than later. Bill. From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Mark Frye Sent: Saturday, March 05, 2011 12:08 PM To: 'RE-wrenches' Subject: Re: [RE-wrenches] grounding the Enphase inverter I guess the thinking is that DC side of the Enphase is grounded and therefore a separately derived system requiring it's own system grounding. This is achieved by connecting the GEC to the chassis of the inverter. If the DC side of the inverter were ungrounded, then it would not be a separately derived system and would not require it's own system ground. At that point, would the AC side of the inverter still be considered a separately derived system or would the need for system grounding go away? Mark Frye Berkeley Solar Electric Systems 303 Redbud Way Nevada City, CA 95959 (530) 401-8024 <http://www.berkeleysolar.com/> www.berkeleysolar.com _____ From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Bill Brooks Sent: Friday, March 04, 2011 5:51 PM To: 'RE-wrenches' Subject: Re: [RE-wrenches] grounding the Enphase inverter The better question is why is there a solid ground in the inverter. As I stated before-we are talking about system grounding-with 100+ years of electrical history and precedent to back it up. System grounding rules are not open to a lot of discussion. That is why my recommendation since before they released their first product was to go ungrounded. Just because it is a pain, and we think there is no technical reason, does not mean we can ignore the rules. As I said in my post, this is not really a safety issue, but it is very much a compliance issue. System grounding is so much a part of our electrical culture, that tiny electrical supplies like PV microinverters were never really considered. Any installer can use the "don't ask, don't tell" method of installation, but once we start down that path, the ability of the human mind to justify actions is limitless. We have to go back to why we ground systems in the first place. It is to prevent the voltage on the system conductors from wondering too far from ground potential. There are other ways to prevent this, but in the U.S. we mostly use conductors (not a variety of conductive materials without clear ratings). The advent of the WEEB, with all its great benefits, does not fundamentally change system grounding. The sooner we get PV systems ungrounded, or resistively grounded, the better the whole U.S. PV industry will be. To that end, everyone should move to PV Cable/Wire and modules with PV Cable/Wire so we are using better products than USE-2 and we can easily transition to ungrounded inverters as they become more available. We already have several so now is not a bad time to start thinking about it. Bill.
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