Hi fellow wrenches forgive me if this has been said. The AC is a special problem on MIcro inverters because the long runs modules to service are now in the AC section of the system. The DC connections are very short. The utility has a +- 5% normal tolerance, which leaves us with only 5% to count on. If the grid is high any voltage rise would put us very close to high voltage shut down. The manufacture is trying to help us prevent nuisance shut downs, and is looking for 1% voltage rise. Voltage rise or drop is easily calculated in English units by Vr=2KIL/CM where K is the coefficient of resistance for copper (12.9) I is the current in amps, (0.82x#of M190 inverters) L is the one way length of the wire run. or equally straight forward is Vr= 2LIR/1000 where the L is the one way length, I is the current as above, R is the resistance per 1000 feet of wire. The CM and R values are from Chapter 9 Table 8 of the NEC Darryl
--- On Fri, 6/11/10, Jeff Yago <[email protected]> wrote: From: Jeff Yago <[email protected]> Subject: Re: [RE-wrenches] AC wiring loss on micro-inverters To: [email protected], "RE-wrenches" <[email protected]> Date: Friday, June 11, 2010, 5:42 PM I just attended a training class in Philly last week by Enphase technical staff and my notes say they suggest up to 15 micro-inverters @ 190 watts each per string with no problem. They also are now shipping their dual module micro-inverter which should help with this wire issue since this model #D380 has two #M190 units built into the same box which is only slightly larger than a single micro-inverter. Since this new dual micro-inverter does NOT have the AC pass-through wire built-in, you are no longer limited to the wire size that comes in and out for the 240 VAC connections. HOWEVER, they require you to purchase this awful looking multi-tap pigtail cable for the AC connections which has a pre-wired connector spaced the expected distance apart the micro-inverters would be installed, and this is a $950 item for every six dual micro-inverters. When I saw this thing I thought is was a python that had swalled six pepsi cans! Not sure what this will look like on a roof or how well it can be hidden behind the array, but it uses a larger wire size so perhaps the wire loss issue has been resolved. Jeff Yago DTI Solar Netscape. Just the Net You Need. -----Inline Attachment Follows----- _______________________________________________ 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
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