Wrenches – I am no code expert, but wanted to chime in to this important discussion.
Rapid shutdown (690.12) does not deal (directly) with arc faults at all. The initiation of rapid shutdown is generally a manual process that a first responder triggers to reduce shock hazard. The RS system is not required to monitor the system for any faults on the DC side. 690.11 (DC arc faults) requires a system to “detect and interrupt arcing faults resulting from a failure in the intended continuity of a conductor, connection, module or other system component”(2017) (by definition a series arc) – and note that this has nothing necessarily to do with a ground fault. A PV module connector that is being pulled apart and the current is arcing across the gap between pins is exactly what this is for – a very good chance that arcs create high enough temperature – even at low current – to start a fire. A ground fault does not need to generate an arc (though likely will). A ground fault is the unintentional electrical connection of a conductor to the grounding system. Removal of insulation of a conductor that is resting on a grounded piece of metallic racking will do. The conductor does not need to be physically compromised, just exposed. Back to the original thread point - I agree that the sudden change in voltage state of the conductors is not optimal, but the delta between DC pos and DC neg will not change. And the intent is that the GFDI fuse will blow when part of that conductive path has been referenced to ground (by the fault) out in the array anyway. So nominal voltage would not be measured out in the array when the ground fault system is needed, right before and after the fuse blows. The Bakersfield fire was the result of many faults occurring due to improper installation techniques, but led to the acknowledgement that the fuse grounding method presents a “blind spot” – the inability to detect a ground fault on the grounded conductor itself. That fault will not necessarily present a hazard (no change in voltage and thus current of the already grounded conductor) but it also will NOT trigger the ground fault detection system. Another fault occurring in the array then may have a return fault path for current that the GFDI fuse blowing cannot stop. Much better summary than I can give here: http://www.solarabcs.org/about/publications/reports/blindspot/ Best regards – Mike SMA America Michael Mahon Technical Trainer, Solar Academy 6020 West Oaks Boulevard, Suite 300 Rocklin, CA 95765 U.S.A. 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Any review, copying, or distribution of this email (or any attachments thereto) by others is strictly prohibited. If you are not the intended recipient, please contact the sender immediately and permanently delete the original and any copies of this email and any attachments thereto. Thank you. From: RE-wrenches <re-wrenches-boun...@lists.re-wrenches.org> On Behalf Of Darryl Thayer Sent: Monday, July 22, 2019 10:18 PM To: William Miller <will...@millersolar.com>; RE-wrenches <re-wrenches@lists.re-wrenches.org> Subject: Re: [RE-wrenches] DC Bonding battery systems Hi Bill, I have thought about it also. The ground fault detection interruption system does elevate one of the conductors to voltage. This makes it hazardous. However, it also protects from a PV hot to ground arc fault. There are three types of arc faults in PV systems, the ground fault arc, the series arc fault, and the parallel arc fault. It is the parallel arc that was addressed in the 2017 NEC via module-level shutdown. The intent of 690.11 can not be addressed without 2017 690.12.b(2) where the detection of an arc must shutdown the array currents. On Mon, Jul 22, 2019 at 3:42 PM William Miller <will...@millersolar.com<mailto:will...@millersolar.com>> wrote: Wrenches: Here is a question that has bothered me for some time: If one is using a GFD (ground fault detection) breaker on a PV feeder(s) to a battery inverter system, the state of the industry is to use a breaker with an extra 0.5 or 1 amp pole. This section of the breaker connects, or bonds the DC negative, or grounded conductor, to the grounding system. In order for the GFD breaker to work one needs to isolate the grounded bus bar (negative). If there is a ground fault the breaker opens and breaks the bond. This goes very much against my conceptualization of how a bonding system should work. The bond should never be broken, particularly when there is a fault in the system. When this breaker opens, either manually or by an overcurrent condition on any pole, the DC bond is removed for all portions of the DC system. There is a prominent personality in the industry that often presents academic opinions on solar related electrical issues in articles and in seminars. This person claimed to have invented this GFD system, but when pressed to comment on the concerns mentioned above, changed the subject. I believe ground fault protection is important. I just don’t believe the method the industry has offered is really effective in solving the issues presented in a ground fault scenario. I believe similar issues present on non-battery PV systems with the simple fuse in the ground system found on many inverters. I know some troubleshooting guides warn of energized parts in ground fault conditions. Have any of you thought about these concerns? Are my concerns valid? What are your policies on this subject? Thanks in advance for any insight. William Miller Miller Solar 17395 Oak Road, Atascadero, CA 93422 805-438-5600 www.millersolar.com<https://eur02.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.millersolar.com%2F&data=02%7C01%7Cmichael.mahon%40sma-america.com%7C8530e26b4e5d4bca4eee08d70f24c44e%7Ca059b96c28294d1188374cc1ff84735d%7C0%7C0%7C636994522897601786&sdata=R09%2B%2FvdKnZC36oAW6Vm4QKTEN%2B%2FFPmo5%2Fq8A6YB1Uus%3D&reserved=0> CA Lic. 773985 Quote of the month: “As they age, batteries transition from energy storage devices to energy consuming devices.“ W. 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