Quote:
Originally Posted by stevehull
Secondly, what diameter (gauge) wire did you bring down from the Enphase output to your electrical panel? The smaller the wire, the greater the resistance loss, but fatter wire is more expensive. Do you have a suggestion on that trade off?
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Personally, my wire run between the trunk cable and the combiner panel is #10 UF 3 conductor + gnd. I went with 10AWG to decrease my resistance/ft, because UF didn't need to be in conduit through the attic, walls, etc. and because it was readily obtainable in a coil, relatively inexpensively (actually cheaper than 12-3 UF at the orange box store for 100ft).
I have 20 panels on the roof. As a result, I have two trunk cables with 10 panels each. I transition from the two Enphase trunk cables to two 4 conductor TCER cables with sunlight + oil resistant jackets on the roof in a Hubbel-Weigmann 8x6x4 fiberglass panel. The two circuits of TCER go down through a weather head to a 6x6x4 Carlon box in the second floor attic where I transition to the twin runs of 10-3 UF. Those twin runs combine in a Square-D QO 100A panel and run via 6 gauge THWN to a 30A breaker in my service entrance panel where I ultimately feed the house or the net meter to the grid, or both.
I figured with 10AWG running from the second floor attic to the combiner panel, even if I some day in the future upgrade my panels to new more efficient designs with 2x the power output, I'll still have adequate wire for the task without serious resistance losses.
Just looking at my Enlighten page, I'm running 109% of PV Watts estimated on my lifetime (since August 1, 2013) using a 0.96 DC to AC derate factor.