Detailed answers to your questions, as I see this issue getting worse...
My questions for the group are; ~ Can any energy-generating device, even if it *was* UL 1741 listed, comply with the NEC if it plugs into a wall outlet instead of being hard-wired to the breaker panel? *** No. Equipment certified and Listed to UL1741 affirms to the extent possible that the inverter itself is safe. The National Electric Code, 690.64(B)(1) mandates connection of grid-tie inverters to a "dedicated" circuit breaker or fusible disconnect. Should a fire result from such an attachment, it's possible and even likely fine print in the homeowner's insurance policy may void coverage for this violation. The probability of a fire depends on several variables: 1) the wattage of the PV and inverter; 2) the loads connected to that particular circuit; and whether the loads and inverter are in operation at the same time, and the total current (utility + inverter-supplied) exceeds the rated current for the conductors. ~ An argument raised by one distributer of these inverters was, "Well, here in (minnesota) the customer owns all the wiring in their house up to the utility feed. So they can plug in anything they want into the house outlets, whether UL listed or not, as long as they don't have a net metering agreement with the utility...because this inverter does not sell electricity to the utility, it only compensates for house usage." Doesn't 1741 still apply here? *** No. UL1741 doesn't apply here. Actual final circuit connection aspects are outside the scope of UL1741. This is an NEC issue. Moreover, the customer does not own the wiring +outside+ their home, nor the grid. ~ What about latching meters? I understand that some types of utility meter will count all generation from the house circuits as electricity used. *** If loads in the home are small, it's possible the utility meter could register back-fed power from a low-wattage grid-tied inverter. Some mechanical meters will rotate backwards, effectively "un-using" power consumed at other times. Other mechanical meters, as you point out, are "latching", preventing back-fed power from registering at all. Without a net metering agreement between a consumer and their utility company, the new "smart" (i.e. digital) meters register all power (incoming AND outgoing) as "consumed", thus the consumer would be *adding* to their monthly bill by the back-fed power, not reducing it. An outlet-connected inverter would be beneficial only if the consumer's home is using more than the inverter is producing at all times (given the size of the inverter and PV, this is probable most of the time), but the amount of energy produced will likely be very small. The customer would money ahead to put their investment into more insulation, sealing leaks, upgrading appliances, etc. ~ Does this stuff scare you folks as badly as it scares me? Sounds like the double-male 120VAC plugs from Y2K. *** Yes. --- And an un-asked question: If these devices aren't permitted by the NEC to be connected to the grid using an AC outlet, why are they allowed on the market? Answer: They're sold to take advantage of uninformed consumers who don't know any better .. don't care .. or both. Sadly, the inverters in of themselves aren't illegal. They are only in violation of the NEC when grid connected, and only then when the consumer is caught. When will consumers get caught? When there's a fire and/or fatality. At that point ratings-seeking reporters will sensationalize it as "dangerous solar equipment" .. which, as Marv pointed out, will leave the solar industry looking like the bad guys. Dan --- On Sat, 3/26/11, Dan Fink <[email protected]> wrote: From: Dan Fink <[email protected]> Subject: [RE-wrenches] Small, non-UL listed direct PV grid-tie inverters and UL 1741 To: "RE-wrenches" <[email protected]> Date: Saturday, March 26, 2011, 11:07 AM Hello esteemed Wrenches; I have been absolutely swamped with inquiries about small, non-UL listed (or "UL listing pending") direct PV grid-tie inverters in the last few weeks. It appears they are arriving in a flood from China and being sold on Ebay, and by other online retailers. They are also being incorporated into home solar products, such as window coverings that have PV cells on the outside, portable PV systems for renters to reduce their bills, etc. The common theme here is that these devices "plug into any wall outlet and reduce your utility bill." My questions for the group are; ~ Can any energy-generating device, even if it *was* UL 1741 listed, comply with the NEC if it plugs into a wall outlet instead of being hard-wired to the breaker panel? For example, a homeowner wiring a 120VAC plug onto an Enphase and running the cord in through the window. ~ An argument raised by one distributer of these inverters was, "Well, here in (minnesota) the customer owns all the wiring in their house up to the utility feed. So they can plug in anything they want into the house outlets, whether UL listed or not, as long as they don't have a net metering agreement with the utility...because this inverter does not sell electricity to the utility, it only compensates for house usage." Doesn't 1741 still apply here? ~ What about latching meters? I understand that some types of utility meter will count all generation from the house circuits as electricity used. ~ Does this stuff scare you folks as badly as it scares me? Sounds like the double-male 120VAC plugs from Y2K. I sure would appreciate some clarification on UL 1741 from the group, though....specifically regarding plugging generation equipment of any sort into a wall outlet. -- Dan Fink Executive Director; Buckville Energy Consulting Buckville Publications LLC NABCEP/IREC/ISPQ accredited Continuing Education Providers http://www.buckville.com/ [email protected] 970.672.4342 (voicemail) 970.373.1311 (fax) _______________________________________________ List sponsored by Home Power magazine List Address: [email protected] 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
