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Old 01-14-14, 09:54 AM   #10
jeff5may
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Quote:
Originally Posted by Exeric View Post
Well, I just found an answer to one of my two questions. It's here:
http://enphase.com/global/files/Enph...Vdrop_M250.pdf

I think I have to rate the neutral wire as if its taking the full current of each of the 2 phases and not derate because of the phase angle difference between the two. It is not impossible that all the power would come from one phase only under unusual circumstances and if the power exceeded the derated current capacity of the neutral wire it wouldn't be good. It also gives a table for guage size and number of microinverters with the run in feet of the home run cable so that completely solves that question.

Now I just need to find the type of homerun cable sheathing that's legal to be exposed for a few feet on the roof. Anyone?
With a grid-tie system, the solar array is using your power utility as a battery. There is no need to run a heavier neutral wire than the other primary wires. The bulk of your power travels through the 2 line wires at equal current, 120 volts per leg, back to the transformer on the pole. There may be a small amount of current flowing between the neutral of your solar array and main load center panel, but normally this current is 5% or less of your main current.

The neutral wire is there mainly in case you lose a leg of your incoming electric service, so the solar array can run at 120 volts or shut down completely. If the solar array does run, its generation capacity is limited to the panels tied to the active leg. In this case, the neutral wire and the active leg carry equal current.
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Exeric (01-14-14)