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NEC article 310.15

    • 4 posts
    July 31, 2019 4:42 AM PDT

    Just a question regarding to article 310.15(B)(7). I am currently using 310.15(B)(7) for sizing a feeder wire size. If I have a single phase feeder 120/208v, will I be able to use 310.15(B)(7)

    • 137 posts
    July 31, 2019 5:00 AM PDT

    It appears the 2017 allows this for a dwelling unit but in previous codes- before the 2017 120/208 was not allowed


    This post was edited by Dennis Alwon at July 31, 2019 5:02 AM PDT
    • 137 posts
    July 31, 2019 5:24 AM PDT

    Remember the feeder must carry the entire load of the dwelling in order to use that section

     

    (7) Single-Phase Dwelling Services and Feeders. For onefamily
    dwellings and the individual dwelling units of two-family
    and multifamily dwellings, service and feeder conductors
    supplied by a single-phase, 120/240-volt system shall be permitted
    to be sized in accordance with 310.15(B)(7)(1) through
    (4).
    For one-family dwellings and the individual dwelling units of
    two-family and multifamily dwellings, single-phase feeder
    conductors consisting of 2 ungrounded conductors and the
    neutral conductor from a 208Y/120 volt system shall be permitted
    to be sized in accordance with 310.15(B)(7)(1) through
    (3).
    (1) For a service rated 100 through 400 amperes, the service
    conductors supplying the entire load associated with a
    one-family dwelling, or the service conductors supplying
    the entire load associated with an individual dwelling unit
    in a two-family or multifamily dwelling, shall be permitted
    to have an ampacity not less than 83 percent of the service
    rating.
    (2) For a feeder rated 100 through 400 amperes, the feeder
    conductors supplying the entire load associated with a
    one-family dwelling, or the feeder conductors supplying
    the entire load associated with an individual dwelling unit
    in a two-family or multifamily dwelling, shall be permitted
    to have an ampacity not less than 83 percent of the feeder
    rating.
    (3) In no case shall a feeder for an individual dwelling unit
    be required to have an ampacity greater than that specified
    in 310.15(B)(7)(1) or (2).
    (4) Grounded conductors shall be permitted to be sized
    smaller than the ungrounded conductors, if the requirements
    of 220.61 and 230.42 for service conductors or the
    requirements of 215.2 and 220.61 for feeder conductors
    are met.