Electrical Service Entrance
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For a service rated 100 amperes 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 a 100 percent service rating. The rest of the service conductors, if any, shall have a service rating not exceeding 50 percent of the service rating. If no adjustment or correction factors are required, Table 310.12 shall be permitted to be applied.
N (A) In a Grounded System. For a service rated 100 amperes 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. If no adjustment or correction factors are required, Table 310.12 shall be permitted to be applied.
N (A) In a Balanced System. For a service rated 100 amperes 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. If no adjustment or correction factors are required, Table 310.12 shall be permitted to be applied.
In accordance with 310.15, a surface service entrance shall be considered a two-family dwelling if at least 30% of the building is in two or more separate structures and the service entrance is on the first level of a building. For example, a residence with an attached garage on the first level and a living space on the second level qualifies as two-family, and service entrance equipment shall be permitted to be installed on the first level of the building. In addition, the single-phase, 120/240-volt service shall be permitted to have an ampacity not less than 83 percent of the service rating. The ampacity of the service shall be based on the applicable single-phase service rating. The service conductors supplying the first floor shall be permitted to have an ampacity not less than 83 percent of the service rating, and conductors supplying the second floor shall have an ampacity not less than 66 percent of the service rating. 827ec27edc