Originally Posted by railfancwb
If I was running 110 volt (or 115 or 120) AC 300 or so feet I would want to use at least #12 2+g underground cable, and use conduit to bring it above ground. #12 is nominally good for 20 amps, but I would not expect to run more than about 15 amps load due to voltage drop at that distance.
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Rule of thumb is to go up one wire size for every 100'
15A circuit normally would use #14, for 300' run use #10