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I have a small building that is 440 ft from the main house, and I want to supply power to it. One 15amp circuit will be sufficient.

What size wire is needed to do this?

Niall C.
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Ian
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  • We really need to know what country you are in to be able to answer that. – Grant Nov 10 '14 at 22:02
  • Just wondering: Are you considering a buried power line, or overhead? (Each has its own hazards and needs to be done properly.) And 15A at what voltage? – keshlam Nov 10 '14 at 22:56
  • This answer, and this answer might be helpful. – Tester101 Nov 10 '14 at 23:52
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    Even though you only need a single circuit right now, you might price out how much more it would cost to run cable for a small subpanel: say 40 or 60 amps, 240V (you don't actually have to install the panel now). That way in the future if you want to run power tools, a small heater, etc., you can just add the panel without redoing all the wiring. – Hank Nov 11 '14 at 15:15

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Using one of the many wire size calculators on the internet, for 120v single phase:

1 conductors per phase utilizing a #3 Copper conductor will limit the voltage drop to 2.59% or less when supplying 15.0 amps for 440 feet on a 120 volt system.

Also, please be sure to use the actual wire length, not just the distance between buildings (eg taking into account depth in ground, height to panels, farthest plug on your circuit, actual path wire will take, etc). With the same parameters, it looks like you can go to about 510 feet before you need to use #2 wire.

gregmac
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