(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-familydwelling, 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-familydwelling, 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.
Where correction or adjustment factors are required by
310.15(B)(2) or (3), they shall be permitted to be applied to
the ampacity associated with the temperature rating of the
conductor.
