As Abraham Lincoln famously said, "I'll give it my best shot, but I'm no Bill Brooks."
A DC ground fault is not impossible on an AC module but it's not the issue that it is on large DC systems where numerous high-voltage parallel strings can feed an array fault. When the unit is listed it's tested to withstand the maximum DC current available from its power source- that 250W-ish module. I don't see any issue with the NEC "intent" relating to DC GFDI when 690.6(D) explicitly states that AC modules "shall be permitted to use a single detection device to detect only ac ground faults, and disable the array by removing ac power." (NEC 2008)
That being said, I can't quite tell what's going on with the AC wire on that datasheet-- it seems that those wires would be dangling (even if installed end-to-end rather than side-by-side), so I'd recommend supporting those above the roof like you're used to doing.
On 2012/2/23 12:08, Bill Hoffer wrote:
Todd I have been researching micro inverters and AC modules for another client and have been wondering about GFDI requirements on the DC side, according to the NEC code an AC module may be permitted to have GFDI on the AC side only, apparently because it has been tested as a " complete , environmentally protected unit ". This is a no brainer with units like the Exceltech AC module which is integrated into the junction box of the module, but the AUO brand seems to be also listed as an AC module which has normal MC4 connectors between the module and inverter (kinda jerry rigged in my opinion). This makes me think that there is a potential for a DC ground fault, but because of the AC Module listing on this unit , as far as I can tell, does not have an integrated GFDI. My main concern is safety and liability, but there seems to be a real gaggle of wiring under the module w/o a good way to protect it from damage on the roof. There could be a situation of a DC ground fault causing a fire on a residence that would result in some legal finger pointing, which I would not like to have pointed back to me as an installer! As far as how well this AC module performs, I have no field experience. There seems to be a real disconnect between UL 1741 requirements and what the testing authorities are calling AC modules and the the intent of the NEC GFDI requirements on the DC side. I am concerned that the final interpretation will fall on the local inspector and cause a lot of grief for us installers. IMHO installers need to beware of this hassle potential and at a minimum insure that their local inspector accepts it before installing and make sure your insurance is up to date! It would be interesting to hear from Bill Brooks on this one! Bill Bill Hoffer PE NABCEP Certified Solar PV Installer™ Sunergy Engineering Services PLLC 2504 Columbia Ave NW East Wenatchee WA 98802-3941 suneng...@gmail.com <mailto:suneng...@gmail.com> Cell:(509)679-6165 _______________________________________________ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Options& settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules& etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
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