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).
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).
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).
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).
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).
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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