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We are putting a 100 amp sub panel in a building with an eye toward making it a small apartment. We will need to run 160 feet of wire from the 200 amp main. We have been told to use 12/2 gauge and 14/2 gauge for wall plugs and lights. What gauge do we need to run between the two boxes? Thanks.

lizabet

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    What is your level of expertise in electrical work?
    – Speedy Petey
    May 2, 2016 at 19:36

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Here is a link to south wire voltage drop calculator your voltage drop should be less than 3%. I entered 240v 160' and 80 amp load since you did not give a value. The calculator provided #3 copper. You would want to use UF cable for direct burial. If you are putting it in conduit you would want to use THWN. Schedule 80 PVC conduit would need to be 1-1/4" for 3 wire or 1-1/2 for 4 wire. In your sub Panel the ground and neutral needs to be isolated many times they are tied together at the factory with a large copper wire connecting the 2 grounded / grounding buss bars. Other than that you should bury this a minimum of 18".

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  • That is 18" if in PVC conduit or 24" if direct burial UF.
    – Eugene Smith
    May 3, 2016 at 5:19
  • There is an exception for 1 and 2 family dwellings driveways and parking areas used for dwelling related purposes at 18" NEC table 300.5 column 1. I usually do go 24 with all UF.
    – Ed Beal
    May 3, 2016 at 13:21

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