The National Electrical Code (NEC) contains an introduction, nine chapters and eight annexes; Article 90 is the introduction to the NEC, and it includes specifications that are essential to the rest of the Code book. The scope is one item covered in the introduction (in 90.2). Most articles have a scope, but there is a difference between this article and all other articles.
Other articles have a scope that describes what is covered in that particular article. The scope in Article 90 details what the NEC covers and what the NEC does not cover. Also covered in the scope of Article 90 is special permission. As stated in 90.2(C), the authority having jurisdiction (AHJ) is permitted to grant exception for the installation of conductors and equipment that are not under the exclusive control of the electric utilities and are used to connect the electric utility supply system to the service-entrance conductors of the premises served. This special permission provision is only possible if such installations are outside a building or terminate immediately inside a building wall. This is the first of approximately 20 Code sections (in 17 articles) containing the term “special permission.”
The term “special permission” also is in Section 90.4. By special permission, the AHJ may waive specific requirements in the NEC or permit alternative methods where it is assured that equivalent objectives can be achieved by establishing and maintaining effective safety. Because the term is essential to the proper application of the Code and it is used in more than one article, it is defined in Article 100. Special permission is the written consent of the AHJ. It is important to note that special permission is not permission in verbal form only; it must be in writing.
Last month’s article covered the calculated load for general lighting and general-use receptacle in 220.82(B)(1). This month, the discussion continues with optional feeder or service load calculations as specified in 220.82.
There are a limited number of occupancy types that can be calculated by optional methods. Occupancy types include dwelling units (one family, two family and multifamily), schools, and new restaurants. The optional calculation for a single-family dwelling starts out the same as the standard method calculation specified in Part III of Article 220. The first step, covered last month, is calculating the general lighting and general-use receptacle load from the square-foot floor area. The next provision is usually broken down into two steps. In accordance with 220.82(B)(2), each 2-wire, 20-ampere (A) small-appliance branch circuit covered in 210.11(C)(1) must be included into the calculation at 1,500 volt-amperes (VA). To calculate, simply multiply the number of small-appliance branch circuits by 1,500 VA. For example, what is the optional service load calculation (before applying the demand factor) for a single-family dwelling that will have five small-appliance branch circuits? Since there are five small-appliance branch circuits, multiply 1,500 by 5 (1,500 5 = 7,500). Before applying the demand factor in 220.82(B), the calculated load for five small-appliance branch circuits in this dwelling is 7,500 VA (see Figure 1).
Although there is no maximum number of small-appliance branch circuits, there is a minimum. In accordance with 210.11(C)(1), at least two 20A small-appliance branch circuits must be provided for all receptacle outlets required by 210.52(B). In the kitchen, pantry, breakfast room, dining room or similar area of a dwelling unit, the two or more 20A small-appliance branch circuits required by 210.11(C)(1) shall serve all wall and floor receptacle outlets covered by 210.52(A), all countertop outlets covered by 210.52(C), and receptacle outlets for refrigeration equipment [210.52(B)(1)]. Therefore, the minimum number of 2-wire, 20A small-appliance branch circuits is two (see Figure 2).
Before finalizing the number of circuits, ensure that receptacles installed in a kitchen to serve countertop surfaces are supplied by at least two small-appliance branch circuits as required by 210.52(B)(3). Either or both of these circuits also shall be permitted to supply receptacle outlets in the same kitchen and in other rooms specified in 210.52(B)(1).
Also in accordance with 220.82(B)(2), each 2-wire, 20A laundry branch circuit covered in 210.11(C)(2) must be included into the calculation at 1,500 VA. For example, what is the optional service load calculation (before applying the demand factor) for a single-family dwelling that will have two laundry branch circuits? Since there are two laundry branch circuits, multiply 1,500 by 2 (1,500 2 = 3,000). Before applying the demand factor in 220.82(B), the calculated load for two laundry branch circuits in this dwelling is 3,000 VA (see Figure 3).
As stipulated in 210.11(C)(2), at least one additional 20A branch circuit shall be provided to supply the laundry receptacle outlet(s) required by 210.52(F). Section 210.52(F) also states that at least one receptacle outlet must be installed for the laundry. There are two exceptions to 210.52(F), but neither is applicable to a one-family dwelling. While it is not required that a dwelling have a clothes-washing machine, it is required that a receptacle outlet, supplied by a 20A branch circuit, be installed for the laundry. A load calculation for a one-family dwelling must include at least one laundry branch circuit rated 1,500 VA when calculating by the optional method (see Figure 4).
Regardless of the size of a one-family dwelling, it must include at least two 20A small-appliance branch circuits and at least one 20A laundry branch circuit. Regardless of how small the one-family dwelling, at least 4,500 VA must be included in the optional method load calculation: 3,000 VA (1,500 2 = 3,000) for the two small-appliance branch circuits and 1,500 VA for the laundry branch circuit.
Next month’s column continues the discussion of feeder and service load calculations.