BranchCircuit, 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
centralstation 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 smallappliance
and laundry loads in 220.52.
Smallappliance
branchcircuit loads must be included in the load calculation when
determining feeder and service loads for dwelling units. In each
dwelling unit, each twowire smallappliance branch circuit required by
210.11(C)(1) must be calculated at 1,500 voltamperes [220.52(A)]. To
comply with this section, simply multiply the number of smallappliance
branch circuits by 1,500 voltamperes.
For
example, what is the service load calculation (before applying any
demand factors) for a onefamily dwelling that will have four
smallappliance branch circuits? Since there are four smallappliance
branch circuits, multiply 1,500 by 4 (1,500 × 4 = 6,000). Before
applying any demand factors, the calculated load for four
smallappliance branch circuits in this dwelling is 6,000 voltamperes
(see Figure 1).
While there is no maximum number of smallappliance
branch circuits, there is a minimum. In accordance with 210.11(C)(1),
at least two 20ampere smallappliance 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 20ampere smallappliance 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
voltamperes for each twowire smallappliance branch circuit
[220.52(A)]. Including smallappliance branchcircuit loads on every
feeder in a dwelling is not required. Unless the feeder will supply
smallappliance branch circuits, do not add smallappliance
branchcircuit loads into the feeder calculation.
For
example, not counting the service equipment, a onefamily dwelling will
have three panelboards. One of the panelboards will supply three
smallappliance branch circuits. The other two panelboards will not
supply any smallappliance branch circuits. A load of 4,500
voltamperes (3 x 1,500 = 4,500) must be included when calculating the
load of the panelboard with the three smallappliance branch circuits.
Since the other two panelboards do not supply any smallappliance
branch circuits, do not include these loads in their calculations.
Not
all circuits in the kitchen are required to be supplied by 20ampere
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 20ampere
smallappliance branch circuit, and the load must be calculated at
1,500 voltamperes. But, if the refrigeration equipment is supplied
from an individual branch circuit, it is permissible to exclude this
load when calculating smallappliance branchcircuit 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 laundrycircuit loads are similar to
smallappliance branchcircuit loads. A load of not less than 1,500
voltamperes shall be included for each twowire 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 20ampere 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 onefamily 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 voltamperes (see Figure 4).
In accordance with 220.52(A) and 220.52(B), the
smallappliance and laundry branchcircuit 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 onefamily dwelling that has a general
lighting load of 12,000 voltamperes? This dwelling also has three
smallappliance branch circuits and two laundry branch circuits. The
calculated load for three smallappliance branch circuits in this
dwelling is 4,500 voltamperes (3 × 1,500). The calculated load for the
two laundry branch circuits is 3,000 voltamperes (2 × 1,500). The
general lighting load, before Table 220.42 demand factors, is 19,500
voltamperes (12,000 + 4,500 + 3,000 = 19,500). The first 3,000
voltamperes remain at 3,000 (3,000 × 100 percent = 3,000). This leaves
16,500 voltamperes (19,500 – 3,000 = 16,500). Multiply the remaining
16,500 voltamperes by 35 percent (16,500 × 35 percent = 5,775). The
general lighting load for this onefamily dwelling is 8,775
voltamperes (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.
