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What size of wire do I need to run from 200 amp meter panel to 100 amp sub panel in detached garage 215' away?

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1 AWG uncoated copper, or 2/0 aluminum. Unless you're not concerned with power quality, then you could do 3 AWG copper or 1 AWG aluminum.

1

Using copper on such a long, heavy run is throwing money away. AA-8000 aluminum is the way to go.

When you punch into the voltage drop calculator, and you say 3%, don't stop there. Go back and try some other numbers. For instance I put in 20% and the answer changed. It said 1/0 aluminum and tells me I'll have 3.8% voltage drop if I do that. And 3.8% is perfectly acceptable. Sure glad I asked.

Why did it say that? Because 1/0 Al is the minimum legal size.

  • Maybe I'm missing something obvious, but why is 1/0 AL "the minimum legal size"? Table 310.15(B)(16) shows 1 AWG AL for 100 amperes @ 75°C. Obviously you're going to be over the 3%, but to my knowledge there's nothing in the code that limits the voltage drop on a feeder. I guess the 1 AWG does assume that the terminals are rated for 75°C, but I think most panel terminals are (but I could be mistaken). – Tester101 Feb 13 '17 at 12:49
  • I'm not sure, I honestly didn't check it, just went with what the calc says. I've never seen it be wrong before. And it doesn't care about loss either, it'll let you take 14AWG 2000 feet if you tell it 95% voltage drop is ok. – Harper Feb 14 '17 at 0:10

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