Micros and conductor sizing

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electro7

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Northern CA, US
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Electrician, Solar and Electrical Contractor
Was looking at a job the other day with 18 enphase microinverters on a home. Planned on one circuit of 10 and one of 8 on two 2-pole 20A breakers. 18 x 1.21A = 21.78 x 1.25 = 27.22A. Can I use #10 awg cu out of the enphase combiner protected by a 30A OCPD? Or do I need to go by the potential of the two 2-pole 20A breakers equalling 40A (#8 on 40A OCPD)?

I guess, if it's okay to use the 30A it would limit future add-ons.

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electro7 said:
Was looking at a job the other day with 18 enphase microinverters on a home. Planned on one circuit of 10 and one of 8 on two 2-pole 20A breakers. 18 x 1.21A = 21.78 x 1.25 = 27.22A. Can I use #10 awg cu out of the enphase combiner protected by a 30A OCPD? Or do I need to go by the potential of the two 2-pole 20A breakers equalling 40A (#8 on 40A OCPD)?

I guess, if it's okay to use the 30A it would limit future add-ons.

Sent from my SM-G998U using Tapatalk
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Are the 2 - 20a breakers going to be in a small subpanel?
Can you put both 20a breakers inside the combiner?
 
Yes they are in the IQ combiner. I was wondering about sizing the feeder to the combiner and the OCPD for it.

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I'll throw another thought into the pot. When the electrician wired my Enphase system, he ran larger than code required size (10AWG vs 12AWG). I being a problem causing EE asked why. He said the line voltage runs high in my area, and he has run into inverters tripping on over voltage with them sourcing into a 124 or 125V line. Mine are M series, not IQ.
 
It has been standard practice in the PV industry forever to oversize wires compared to typical loads, and inmany cases it's required. One reason is to the avoid losses due to voltage drop. (These systems run at full current for hours on end some days, so losses add up.) Another is rooftop derating requirements. AC voltage range for microinverters is another reason. I have never seen a conductor in a PV system smaller than 10AWG (with the exception of manufacturer supplied wiring for the PV array components themselves).
 
Thanks guys. I was wondering about that combiner output circuit sizing.

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GeorgeB said:
I'll throw another thought into the pot. When the electrician wired my Enphase system, he ran larger than code required size (10AWG vs 12AWG). I being a problem causing EE asked why. He said the line voltage runs high in my area, and he has run into inverters tripping on over voltage with them sourcing into a 124 or 125V line. Mine are M series, not IQ.
Click to expand...
Wonder if that would be the last inverter on the string tripping?
 
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