In the previous article " Receptacle Branch Circuit Design Calculations – Part One ", I explained the essential definitions for receptacles branch circuit and the different types of receptacles.
Also, in the previous article " Receptacle Branch Circuit Design Calculations – Part Two ", I explained basic principles, GFCI protection and AFCI protection for receptacle branch circuits.
Today, I will explain the Receptacle Branch circuit calculations for both Dwelling and Nondwelling buildings as follows.
First: Receptacle Branch circuit calculations in dwelling buildings
1 Essential definitions:
As I mentioned before in previous article " Branch Circuit Design Calculations – Part Two " that the Dwelling Building is A single unit, providing complete and independent living facilities for one or more persons, including permanent provisions for living, sleeping, cooking, and sanitation.
Dwelling buildings include the following types:
 Dwelling, OneFamily: A building that consists solely of one dwelling unit.
 Dwelling, TwoFamily: A building that consists solely of two dwelling units.
 Dwelling, Multifamily: A building that contains three or more dwelling units.
2 Receptacle Branch circuit ratings and permissible loads
In no case shall the load exceed the branchcircuit ampere rating. The following are the permissible Receptacle Branch circuit ratings in dwelling buildings:
A) 15 and 20Ampere Branch Circuits
15 and 20Ampere Branch Circuits shall be permitted to supply:
1 Only lighting units: this case explained before in previous article
2 Only utilization equipment: with condition that the combined load for all utilization equipment must not exceed the branch circuit rating.
3 Combination of both: in the case the permissible rating of the utilization equipment will depend on its type as follows:
 If it is not fastenedinplace, it can have a rating of up to 80 % of the branch circuit rating as in TABLE 210.21(B)(2).
 If it is fastenedinplace, other than luminaires, it shall not exceed 50 % of the branchcircuit ampere rating.
Important!!!
Using fastenedinplace equipment is not permitted
for the smallappliance branch circuits, laundry branch circuits, and
bathroom branch circuits required in a dwelling unit and these branch
circuits shall supply only their receptacle outlets required by the code.

B) 30Ampere Branch Circuits
A 30ampere branch circuit shall be permitted to supply utilization equipment in any occupancy. A rating of any one cordandplugconnected utilization equipment shall not exceed 80 percent of the branchcircuit ampere rating.
Important!!!
A single receptacle installed on an individual
branch circuit shall have an ampere rating not less than that of the branch
circuit.

C) 40 and 50Ampere Branch Circuits
A 40 or 50ampere branch circuit shall be permitted to supply cooking appliances that are fastened in place in any occupancy.
3 Selecting Receptacle rating for a branch circuit
A Receptacle rating, general
Where connected to a branch circuit supplying two or more receptacles or outlets, receptacle ratings shall conform to the values listed in Table 210.21(B) (3), or, where rated higher than 50 amperes, the receptacle rating shall not be less than the branchcircuit rating.
B Single Receptacle on an Individual Branch Circuit (see below image)
A single receptacle installed on an individual branch circuit shall have an ampere rating not less than that of the branch circuit. For example, a single receptacle on a 20ampere individual branch circuit must be rated at 20 amperes.
C Receptacle supplying Total CordandPlugConnected Load
Where connected to a branch circuit supplying two or more receptacles or outlets, receptacle ratings shall conform to the values listed in Table 210.21(B) (3), or, where rated higher than 50 amperes, the receptacle rating shall not be less than the branchcircuit rating.
B Single Receptacle on an Individual Branch Circuit (see below image)
A single receptacle installed on an individual branch circuit shall have an ampere rating not less than that of the branch circuit. For example, a single receptacle on a 20ampere individual branch circuit must be rated at 20 amperes.
C Receptacle supplying Total CordandPlugConnected Load
a Receptacle shall not supply a total cordand plug connected load in excess of the maximum specified in Table 210.21(B)(2).
4 Voltage ratings for Receptacle Branch circuit
In dwelling units the voltage rating for Receptacle Branch circuit shall not exceed the following:
A) 120 volts, nominal, between conductors
For Receptacle Branch circuit that supplies Cordandplugconnected loads 1440 voltamperes, nominal, or less or less than 1⁄4 hp.
B) 208volt or 240volt circuit, nominal, between conductors
For Receptacle Branch circuit that supplies Highwattage cordandplugconnected loads, such as electric ranges, clothes dryers, and some window air conditioners.
5 The Maximum allowable number of receptacles on a branch circuit
As per NEC section 220.14(I), Receptacle outlets load (see below image) shall be calculated at not less than:
 180 voltamperes for each single receptacle,
 180 voltamperes for each multiple receptacle (duplex or triplex) on one yoke,
 90 volt amperes per receptacle for multiple receptacles (four or more).
Important!!!
If
a receptacle is dedicated for a specific device, then the actual load is used
and If this dedicated load is continuous, then the 125% overrate is
appropriate.

To calculate the Maximum allowable number of receptacles on a branch circuit, make the following steps:
 Step#1: Determine the maximum circuit power by Multiply the branch circuit voltage and amperage.
 Step#2: Then divide by 180 voltamperes.
Example#1:
How many receptacles can be placed on a 120volt, 20amp circuit? How many can be placed on a 120volt, 15amp circuit?
Solution:
Step#1:
Determine the maximum circuit power (for 20amp circuit) = 120 V × 20 A = 2400 VA
Determine the maximum circuit power (for 15amp circuit) 120 V × 15 A = 1800 VA
Step#2:
Determine the maximum circuit power (for 20amp circuit) = 120 V × 20 A = 2400 VA
Determine the maximum circuit power (for 15amp circuit) 120 V × 15 A = 1800 VA
Step#2:
Then divide the power by the load per receptacle
For 20amp circuit:
Maximum allowable number of receptacles = 2400 VA / 180 VA = 13.3
For 15amp circuit:
Maximum allowable number of receptacles = 1800 VA / 180 VA = 10
So,
A 120volt, 20amp circuit can supply 13 receptacles.
A 120volt, 15amp circuit can supply 10 receptacles.
6 The Minimum number of receptacle branch circuits for bank or office buildings
As per NEC section 220.14(J), if the number of receptacles is unknown so for bank and office buildings, we can calculate the receptacles load by multiplying the area in ft2 by the unit value (1 VA/ft2).
To get the required number of receptacle branch circuits for bank or office buildings make the following steps:
 Step#1: Calculate the total receptacles load for the whole building as explained above.
 Step#2: Calculate the total receptacle circuit load in VA by multiplying its voltage by its amperage as follows:
 For 15A Branch circuits = 120 V × 15 A = 1800 VA
 For 20A Branch circuits = 120 V × 20 A = 2400 VA
 Step#3: Divide the total receptacle load for the whole building by the maximum load per circuit to determine the minimum number of circuits.
Example#2:
Determine the total receptacle load for an 80 ft × 120 ft office building? And determine the number of 15amp circuits needed to supply the load. Noting that the number of receptacles is unknown.
Solution:
Step#1:
The number of receptacles is unknown, so a receptacle load of 1 VA/ft2 can be calculated:
Area = 80 ft × 120 ft = 9600 ft2
Total Receptacle load = 1 VA/ft2 × 9600 ft2 = 9600 VA
Step#2:
To determine the number of circuits required, first calculate the allowable load for a single circuit:
The allowable load for a single circuit = 120 V × 15 A = 1800 VA
Step#3:
Divide the total receptacle load by the maximum load per circuit to determine the minimum number of circuits:
Minimum number of 15A receptacle Circuits = 9600 VA / 1800 VA = 5.33
This is the minimum number, so round up to six circuits.
Important!!!
As per NEC section 220.14(J), limit using the unit
value (1 VA/ft2) for banks and office buildings but it can be used also (as
approximate) for other types of buildings including dwelling ones.

7 Receptacle branch circuits Calculations in dwelling buildings
In the broad sense, Receptacle in dwelling units may serve one of the following loads:
 Generaluse Receptacle Loads,
 Small appliance Loads,
 Laundry Load,
 Fastenedinplace Appliance loads,
 Cloth dryer Load,
 Household cooking appliances load,
 Heating and air conditioning loads,
 Motor loads.
In the following paragraphs, I will explain Where and how to distribute each load outlets in a dwelling building as per NEC code.
1 Generaluse Receptacle Loads
1.1 locations of Generaluse Receptacle Loads as per NEC section 210.52
Rule#1: Main rule
(see below image)
Receptacles shall be installed such that no point measured horizontally
along the floor line of any wall space is more than 1.8 m (6 ft) from a
receptacle outlet.

The wall space is a wall unbroken along the floor line by doorways, fireplaces, archways, and similar openings and may include two or more walls of a room (around corners), as illustrated in Exhibit 210.27. The Minimum length for a wall space is 2 ft.
Important!!!
The
wall space behind the swing of a door is included in the measurement. This
does not mean that the receptacle outlet has to be located in that space,
only that the space is included in the wallline measurement.

Rule#2: electric
baseboard heaters builtin receptacle (see below image)
If there is a permanently installed electric baseboard heaters (longer
than 12 ft.) equipped with factoryinstalled receptacle outlets or outlets
provided as a separate assembly by the manufacturer shall be permitted as the
required outlet or outlets for the wall space utilized by such permanently
installed heaters (see image below) . Such receptacle outlets shall not be
connected to the heater circuits.

Rule#3: Receptacle
designed for intended use
Receptacle designed for intended utilization equipment or practical
room use may be placed in corners, may be grouped, or may be placed in a
convenient location. For example, receptacles in a living room and family
room that are intended to serve home entertainment equipment or home office
equipment.

Rule#4: floor
Receptacles (see below image)
Receptacle outlets in floors shall not be counted as part of the
required number of receptacle outlets unless located within 450 mm (18 in.)
of the wall.

Rule#5: kitchen and
dining areas counters receptacles other than that used for small appliances
(see above image)
Receptacle outlets installed to serve kitchen or dining area counters
(for small appliances) cannot also be used as generaluse receptacles for an
adjacent wall space and in this case generaluse receptacle branch circuits
must be added to serve such locations.

Rule#6: receptacles
not under main rule
The following receptacles can't be used as generaluse receptacles (
rule#1 will not apply for it):
A receptacle that is Part of a luminaire or appliance, or
A receptacle that is controlled by a wall switch, or
A receptacle that is Located within cabinets or cupboards, or
A receptacle that is located more than 1.7 m (5.5 ft) above the floor.

Important!!!
A receptacle controlled by a
switch may result in the occupant using an extension cord, run from an outlet
or device that is not controlled by a switch, to supply appliances or
equipment that require continuous power, such as an electric clock. So, this
receptacle not considered as generaluse receptacle.

In the next article, I will continue explaining Where and how to distribute each receptacle load outlets in a dwelling building as per NEC code. Please, keep following.
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