I need to run 110 volts AC 300' to a subpanel. What size copper wire do I need? Wire will be run in conduit underground.

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    How many amps do you need to carry? – kicken Oct 12 '19 at 16:38
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    What are you trying to power here? – ThreePhaseEel Oct 12 '19 at 18:53
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    The answer is "None. You use aluminum." Except for very small circuits, or certain cases where a transformer+#12 wire prices out as cheapest. By "small" I mean how much stuff is being powered; this is measured in one of these figures: Amps, Watts, or VA. If you're not sure on that stuff, then a) tie an email to your account, b) log in to a real computer, and c) edit your question to include a good essay-sized 200-500 word discussion of what exactly you intend to power in that location. It is impossible to answer without this data. – Harper - Reinstate Monica Oct 12 '19 at 20:17
  • And if it is to a subpanel, rather than a single circuit (unless it is "subpanel that only powers one circuit and using a subpanel as a shutoff switch, which is OK but overkill), then 240V would use 50% more wire but get you 100% more power/circuits. – manassehkatz-Moving 2 Codidact Oct 13 '19 at 0:44

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