What Is The Nec Citation For Minimum Service Size Allowed In A Single Family Dwelling

Table 310.15(B)(7) has been deleted and replaced with a simple 83% factor.

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Table 310.fifteen(B)(7) has been deleted and replaced with a simple 83% factor.

Lawmaking Change Summary: Table 310.15(B)(vii) has been deleted and replaced with an 83% calculation.

Section 310.15(B)(7) contains rules on calculating the conductor size for 120/240-volt, 3-wire, single-phase dwelling services and feeders. In the 2011 NEC, a simple table existed showing the service size on the left and the minimum size conductor required to supply the service on the correct.

To use the table, i would first decide the minimum size service or feeder by using the load calculations in Commodity 220 and then select the minimum size conductor from Tabular array 310.15(B)(seven).

In the 2014 NEC, the tabular array has been deleted and replaced with a uncomplicated 83% which results in the same concluding value as if the table had just been allowed to remain.

Example: A 120/240-Volt, three-Wire, unmarried-stage electric service for a single family unit home with a calculated load (from Article 220) of 98 amps, supplied by THWN copper overhead service entrance conductors.

A 100 amp electric service will be used to supply the 98 amp load for the unmarried family dwelling.

100 amps X 83% = 83 amps. This is the minimum required service conductor.

Take 83 amps and utilise the 75°C column in Table 310.xv(B)(16) to determine that the service requires 4 AWG copper, type THWN overhead service archway conductors.

A close await at the former deleted table shows the same results.

Below is a preview of the NEC. See the actual NEC text at NFPA.ORG for the complete lawmaking department. Once there, click on the "free access" tab and select the applicative year of NFPA lxx (National Electrical code).

2011 Code language:

310.xv(B)(7) 120/240-Volt, 3-Wire, Single-Phase Domicile Services and Feeders. For private abode units of one-family, two-family unit, and multifamily dwellings, conductors, as listed in Tabular array 310.15(B)(7), shall be permitted as 120/240-volt, three-wire, single-phase service-entrance conductors, service-lateral conductors, and feeder conductors that serve equally the main power feeder to each dwelling unit and are installed in raceway or cable with or without an equipment grounding usher. For application of this section, the master power feeder shall exist the feeder betwixt the master disconnect and the panelboard that supplies, either by branch circuits or by feeders, or both, all loads that are part or associated with the abode unit. The feeder conductors to a dwelling unit shall non exist required to take an allowable ampacity rating greater than their service-entrance conductors. The grounded conductor shall be permitted to be smaller than the ungrounded conductors, provided the requirements of 215.2, 220.61, and 230.42 are met.

2014 Lawmaking Linguistic communication:

310.fifteen(B)(seven) 120/240-Volt, Single-Phase Dwelling Services and Feeders. For i-family dwellings and the individual dwelling units of ii-family unit and multifamily dwellings, service and feeder conductors supplied by a single-phase, 120/240-volt system shall be permitted exist sized in accordance with 310.15(B)(vii)(1) through (4).

(one) For a service rated 100 through 400 A, the service conductors supplying the entire load associated with a one-family dwelling, or the service conductors supplying the unabridged load associated with an individual dwelling unit in a ii-family or multifamily dwelling, shall exist permitted to take an ampacity not less than 83 percent of the service rating.

(2) For a feeder rated 100 through 400 A, the feeder conductors supplying the entire load associated with a one-family dwelling, or the feeder conductors supplying the unabridged load associated with an individual dwelling, unit in a two-family unit or multifamily dwelling house, shall exist permitted to accept an ampacity non less than 83 percent of the feeder rating.