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What is the recommended wire thickness to run between 125-150ft to a detached shed (home office)? I was thinking 60 amp breaker, 4/3 thwn-2 (2 hot, 1 neutral, 1 ground). Do I need more?

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  • How many square feet is said shed, and how is it heated/cooled? What size is the service you're trying to run this off of? Dec 27 '20 at 0:10
  • Stating 4/3 with ground ? But then thwn-2 would require conduit a 4 wire feed will be needed unless in metallic conduit allowed to be used as the ground. you don’t provide a load so providing the correct wire size other than the feeder breaker that you have. Check out south wire and there voltage drop calculator.
    – Ed Beal
    Dec 27 '20 at 0:17
  • @ThreePhaseEel - 120 sqft, 200amp main, no heating or cooling.
    – Merkd
    Dec 27 '20 at 0:38
  • What are you running the THWN in, by the way? Dec 27 '20 at 2:18
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#4 THWN aluminum is exactly what I'd use.

As far as voltage drop, 150' isn't far enough for voltage drop to become a concern. I don't even run the numbers until 180' :)

#4 THWN aluminum breakers at 70A (it's rated for 65A but you round up to the next breaker size which exists).

Because it's capable of 70A, you need a 70A ground wire, which is #8 copper or #6 aluminum. If aluminum, it must be insulated. You're allowed to use #4 aluminum, and the benefit is that you get to use black wire and mark it green with phase tape. #8 or #6 ground would need to be actually green or bare.

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