Branch-Circuit, Feeder and Service Calculations, Part XVIII

by Charles R. Miller
Published: August 2007

Article 220 – Load Calculations

220.52 Small Appliance and Laundry Loads—Dwelling Unit

In 1882, New York City was home to the first central-station electric generating plant developed by Thomas A. Edison. By 1895, there were as many as five different electric installation codes in use throughout the United States. In March 1896, a group of people met to develop a national set of rules for electrical construction and operation. Upon completion, 1,200 knowledgeable and concerned individuals in North America and Europe reviewed these new regulations. In 1897, the National Electrical Code (NEC) was born. The National Fire Protection Association (NFPA) assumed sponsorship and control of the NEC in 1911.

The NEC is divided into three segments: an introduction, nine chapters and annexes. In Chapter 90, the Introduction, the NEC states its purpose is the practical safeguarding of people and property from hazards arising from the use of electricity. As specified in 90.1(C), the NEC is not intended as a design specification or an instruction manual for untrained people.

Last month’s Code in Focus concluded by covering fixed electric space heating calculations in 220.51. This month, the discussion continues with small-appliance and laundry loads in 220.52.

Small-appliance branch-circuit loads must be included in the load calculation when determining feeder and service loads for dwelling units. In each dwelling unit, each two-wire small-appliance branch circuit required by 210.11(C)(1) must be calculated at 1,500 volt-amperes [220.52(A)]. To comply with this section, simply multiply the number of small-appliance branch circuits by 1,500 volt-amperes.

For example, what is the service load calculation (before applying any demand factors) for a one-family dwelling that will have four small-appliance branch circuits? Since there are four small-appliance branch circuits, multiply 1,500 by 4 (1,500 × 4 = 6,000). Before applying any demand factors, the calculated load for four small-appliance branch circuits in this dwelling is 6,000 volt-amperes (see Figure 1).

 
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While there is no maximum number of small-appliance branch circuits, there is a minimum. In accordance with 210.11(C)(1), at least two 20-ampere 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 20-ampere 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)] (see Figure 2).

 
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Where the load is subdivided through two or more feeders, the calculated load for each shall include not less than 1,500 volt-amperes for each two-wire small-appliance branch circuit [220.52(A)]. Including small-appliance branch-circuit loads on every feeder in a dwelling is not required. Unless the feeder will supply small-appliance branch circuits, do not add small-appliance branch-circuit loads into the feeder calculation.

For example, not counting the service equipment, a one-family dwelling will have three panelboards. One of the panelboards will supply three small-appliance branch circuits. The other two panelboards will not supply any small-appliance branch circuits. A load of 4,500 volt-amperes (3 x 1,500 = 4,500) must be included when calculating the load of the panelboard with the three small-appliance branch circuits. Since the other two panelboards do not supply any small-appliance branch circuits, do not include these loads in their calculations.

Not all circuits in the kitchen are required to be supplied by 20-ampere circuits; there is an exception for refrigeration equipment supplied from an individual branch circuit. The receptacle outlet for refrigeration equipment shall be permitted to be supplied from an individual branch circuit rated 15 amperes or greater [210.52(B)(1), Ex. No. 2]. If the refrigeration equipment is not supplied by an individual branch circuit, it must be supplied by a 20-ampere small-appliance branch circuit, and the load must be calculated at 1,500 volt-amperes. But, if the refrigeration equipment is supplied from an individual branch circuit, it is permissible to exclude this load when calculating small-appliance branch-circuit loads. The individual branch circuit permitted by 210.52(B)(1), Exception No. 2, shall be permitted to be excluded from the calculation required by 220.52 [220.52(A) Ex.] (see Figure 3).

 
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Calculations for laundry-circuit loads are similar to small-appliance branch-circuit loads. A load of not less than 1,500 volt-amperes shall be included for each two-wire laundry branch circuit installed as required by 210.11(C)(2) [220.52(B)]. In accordance with 210.11(C)(2), at least one additional 20-ampere branch circuit must be provided to supply the laundry receptacle outlet(s) required by 210.52(F). For example, what is the service load calculation (before applying any demand factors) for a one-family dwelling that will have one laundry branch circuit? Since there is only one laundry branch circuit, the load (before applying any demand factors) in this dwelling is 1,500 volt-amperes (see Figure 4).

 
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In accordance with 220.52(A) and 220.52(B), the small-appliance and laundry branch-circuit loads can be included with the general lighting loads and subjected to the demand factors provided in Table 220.42. For example, what is the general lighting load, after applying demand factors, for a one-family dwelling that has a general lighting load of 12,000 volt-amperes? This dwelling also has three small-appliance branch circuits and two laundry branch circuits. The calculated load for three small-appliance branch circuits in this dwelling is 4,500 volt-amperes (3 × 1,500). The calculated load for the two laundry branch circuits is 3,000 volt-amperes (2 × 1,500). The general lighting load, before Table 220.42 demand factors, is 19,500 volt-amperes (12,000 + 4,500 + 3,000 = 19,500). The first 3,000 volt-amperes remain at 3,000 (3,000 × 100 percent = 3,000). This leaves 16,500 volt-amperes (19,500 – 3,000 = 16,500). Multiply the remaining 16,500 volt-amperes by 35 percent (16,500 × 35 percent = 5,775). The general lighting load for this one-family dwelling is 8,775 volt-amperes (3,000 + 5,775 = 8,775) (see Figure 5).

 
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Next month’s Code in Focus continues the discussion of feeder and service load calculations.

MILLER, owner of Lighthouse Educational Services, teaches classes and seminars on the electrical industry. He is the author of “Illustrated Guide to the National Electrical Code” and NFPA’s “Electrical Reference.” He can be reached at 615.333.3336, charles@charlesRmiller.com or www.charlesRmiller.com.

 
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