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Our home has a 200 AMP main service disconnect and a 200 AMP sub-panel inside the house. The barn is about 200 feet away with a small sub-panel and is currently fed by a an overhead 8/3 wire. I plan to install solar panels on the barn roof (5-kw array) and connect the inverter to to the barn's sub-panel.

Do I need to increase the size of the wire feeding the barn? It will be carrying all the electricity produced by the solar panels. How do I know what size wire is appropriate? Also, I plan to put any replacement wire underground in conduit.

Thanks for your help.

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I am assuming that you have 220V going to the barn? As far as wire size, industry standards say to aim for 1 - 2% voltage drop, but running 5000W, 200ft on #8 wire @ 220V results in just under 3% voltage drop. This will probably work just fine but it would work a little better if you were to upgrade it to a #6 or a #4. It is just a matter of weighing the options. During peak performance a system running at 5000W with a 3% drop would be losing around 150W. At 1% drop you would only lose 50W remember, this is only during peak performance; during the morning and evening, your losses are much less.

Here is the question to ask yourself... How much money is it going to cost to upgrade the wire? Is it worth it for a 100W increase?

Credits: I mostly use the Southwire Voltage Drop Calculator for my calculations... I can do it manually but the Vdrop calculator is much easier.

Thanks, Maxfield Solar

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