152 Modern Commercial Wiring
Copyright Goodheart-Willcox Co., Inc.
can be used as a replacement for an ungrounded recep-
tacles outlet.
A load of 180 volt-amperes is assigned to each recep-
tacle, whether it is single, duplex, or triplex. If a recep-
tacle is dedicated for a specific device, then the actual
load is used. If the dedicated load is continuous, then the
125% overrate is appropriate.
To calculate the allowable number of receptacles on a
branch circuit, multiply the circuit voltage and amperage,
then divide by 180 volt-amperes. The receptacle load can
be included with the general lighting load by adding a
value of 1 VA/ft2 to the general lighting unit loads found in
Table 220.12. However, this method should only be used
when the number of receptacles is unknown.
Sample Problem 12-7
Problem: How many receptacles can be placed on
a 120-volt, 20-amp circuit? How many can be
placed on a 120-volt, 15-amp circuit?
Solution: Determine the maximum circuit power:
= 120 V × 20 A
= 2400 VA (for 20-amp circuit)
P = E × I
= 1800 VA (for 15-amp circuit)
P = 120 V × 15 A
Then divide the power by the load per receptacle
(180 volt-amperes):
20-amp circuit:
2400 VA
180 V
=
13.3
15-amp circuit:
1800 VA
180 V
=
10
A 120-volt, 20-amp circuit can supply 13 receptacles.
A 120-volt, 15-amp circuit can supply 10 receptacles.
Multioutlet assemblies are frequently installed in
repair shops, lighting display areas, electronics depart-
ments, and other locations where many outlets are
needed. These multioutlet assemblies require 180 volt-
amperes for each 5′ of length. In stores, repair shops, and
laboratories, the Code allows the overall load to be
derated in accordance with Table 220.44 (if the load
exceeds 10,000 volt-amperes).
The diversity and inconsistent loading of general
purpose receptacles allows the total receptacle load to be
derated (see Section 220.44). If the load exceeds 10,000
volt-amperes, the first 10 kilowatts are counted at 100%,
but additional load is counted at 50%. This may not be
used if the Code dictates that the specific appliances
cannot be derated. Refer to Sections 220.12 and 220.44
and Table 220.44.
Sample Problem 12-8
Problem: Determine (a) the receptacle load for an
80′ × 120′ hardware store and (b) the number of
15-amp circuits needed to supply the load. The
number of receptacles is unknown.
Solution: (a) The number of receptacles is
unknown, so a receptacle load of 1 VA/ft2 can be
calculated:
Area = 80′ × 120′
= 9600 ft2
Receptacle load = 1 VA/ft2 × 9600 ft2
= 9600 VA
(b) To determine the number of circuits required,
first calculate the allowable load for a single circuit:
Max load = 120 V × 15 A
= 1800 VA
Divide the total receptacle load by the maximum
load per circuit to determine the minimum number
of circuits:
Circuits =
= 5.33
9600 VA
1800 V
This is the minimum number, so round up to six
circuits.
Figure 12-5. Receptacle ratings are determined by the circuit
rating.
Circuit Rating (A) Receptacle Rating (A)
15 Not over 15
20 15 or 20
30 30
40 40 or 50
50 50
Receptacle Rating