Receptacle Branch Circuit Design Calculations – Part Four

In the previous article " Receptacle Branch Circuit Design Calculations – Part Three ", I explained the following points:

  1. Receptacle Branch circuit ratings and permissible loads,
  2. How to select Receptacle rating for a branch circuit,
  3. Voltage ratings for Receptacle Branch circuit,
  4. How to calculate The Maximum allowable number of receptacles on a branch circuit,
  5. How to calculate The Minimum number of receptacle branch circuits for bank or office buildings.

Also, I stated that a Receptacle in dwelling units may serve one of the following loads:

  1. General-use Receptacle Loads,
  2. Small appliance Loads,
  3. Laundry Load,
  4. Fastened-in-place Appliance loads,
  5. Cloth dryer Load,
  6. Household cooking appliances load,
  7. Heating and air conditioning loads,
  8. Motor loads.

You can review the following previous articles for more information: 

In the following paragraphs, I will explain Where and how to distribute each load outlets in a dwelling building as per NEC code.

1- General-use Receptacle Loads

1.1 locations of General-use Receptacle Loads

the locations of General-use Receptacle Loads as per NEC section 210.52 is controlled by eleven (11) Rules as follows:

The primary objective of the requirements covering any of the dwelling areas included in 210.52 is to minimize the need to use extension cords to supply utilization equipment.

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.

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 wall-line measurement.

Rule#2: electric baseboard heaters built-in receptacle (see below image)

If there is a permanently installed electric baseboard heaters (longer than 12 ft.) equipped with factory-installed 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 general-use receptacles for an adjacent wall space and in this case general-use 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 general-use 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.

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 general-use receptacle.

Rule#7: hallways

As per NEC section 210.52(H), In dwelling units, hallways of 3.0 m (10 ft) or more in length shall have at least one receptacle outlet.
The hallway length shall be considered the length along the centerline of the hallway without passing through a doorway.

Rule#7 does not apply to common hallways of hotels, motels, apartment buildings, condominiums, and similar occupancies.

Rule#8: foyers

As per NEC section 210.52(I), Foyers that are not part of a hallway in accordance with 210.52(H) and that have an area that is greater than 5.6 m2 (60 ft2) shall have a receptacle(s) located in each wall space 900 mm (3 ft) or more in width and unbroken by doorways, floor-to-ceiling windows, and similar openings.

Rule#9: Bathroom

As per NEC Section 210.52(D), in dwelling units, at least one receptacle outlet shall be installed in bathrooms in one of the following locations:
  1. Within 900 mm (3 ft) (36 inch) of the outside edge of each basin.
  2. on the side or face of the basin cabinet not more than 300 mm (12 in.) below the basin countertop.

special cases for Rule#9 are as follows:
  1. If there is more than one basin, a receptacle outlet is required adjacent to each basin location.
  2. If the basins are in close proximity, one receptacle outlet installed between the two basins can be used to satisfy this requirement as shown in below image (top).

A bathroom is defined in Article 100 as “an area including a basin with one or more of the following: a toilet, a urinal, a tub, a shower, a bidet, or similar plumbing fixtures.”

As per NEC section 406.9(C), it is prohibited to install a receptacle within or directly over a bathtub or inside a shower stall even if the receptacles are installed in a weatherproof enclosure.

As per NEC section 210.11(C)(3), At least one 20-ampere branch circuit shall be provided to supply bathroom receptacle outlet(s). This circuit is permitted to supply the required receptacles in more than one bathroom as show in above image (bottom).

If the circuit supplies the required receptacle outlet in only one bathroom, it is allowed to also supply fastened-in-place equipment (lighting and an exhaust fan) in that bathroom, provided the lighting and fan load does not exceed 50 % of the branch-circuit ampere rating as per NEC  section 210.23(A)(2).

Rule#10: Outdoors (see below image)

As per NEC section 210.52(E), Outdoor receptacle outlets shall be installed in accordance with the following:

1- for One-Family and Two-Family Dwellings

For a one family dwelling and each unit of a two-family dwelling that is at ground level, at least one receptacle outlet accessible while standing at grade level and located not more than 2.0 m (6.5 ft) above grade shall be installed at the front and at the back of each dwelling.

2- for Multifamily Dwellings

For each dwelling unit of a multifamily dwelling where the dwelling unit is located at grade level and provided with individual exterior entrance/ egress, at least one receptacle outlet accessible from grade level and not more than 2.0 m (6.5 ft) above grade shall be installed.

3- for Balconies, Decks, and Porches
Balconies, decks, and porches that are accessible from inside the dwelling unit and having an overall area of 20 ft2 or more must have at least one receptacle outlet installed within its perimeter. This receptacle shall not be located more than 2.0 m (6.5 ft) above the balcony, deck, or porch surface.

Where outdoor heating, air conditioning, or refrigeration (HACR) equipment is located at grade level , the receptacle outlets required by this section “which shall be located on the same level” can be used to comply with the receptacle outlet requirement of 210.63, provided that at least one of the outlets is located within 25 ft of the HACR equipment.

The receptacle outlet required for Balconies, Decks, and Porches can also be used to meet the above outdoor receptacle requirements of One-Family, Two-Family and Multifamily Dwellings.

Rule#11: Basements, Garages, and Accessory Buildings (see below image)

As per NEC section 210.52(G), For a one-family dwelling, the following provisions shall apply:
At least one receptacle outlet, in addition to those for specific equipment (Laundry for example), shall be installed in each basement, in each attached garage, and in each detached garage or accessory building with electric power.
Where a portion of the basement is finished into one or more habitable rooms, each separate unfinished portion shall have a receptacle outlet installed in accordance with this section.

Where detached garages are not supplied with electricity, receptacle outlets do not have to be installed.

1.2 Calculation of general-use receptacles load

A- For feeder and service calculation purposes

As I mentioned before in previous article that In one-family, two-family, and multifamily dwellings and in guest rooms or guest suites of hotels and motels, The general lighting load unit values specified in table 220.12 (which was 3VA/ft2) will include the following receptacle loads:

  1. All general-use receptacle outlets of 20-ampere rating or less, including receptacles connected to Bathroom Branch Circuits, 
  2. The outdoor receptacle outlets, 
  3. General-use receptacle Outlets used in Basements, Garages, and Accessory Buildings. 

So, No additional load calculation is required for general-use receptacle loads i.e. general use receptacle loads (after applying the general lighting load unit value from table 220.12) = Zero.


A homeowner wants to add 10 numbers general-purpose Receptacles, what is the additional load to the service?


No additional load calculation is required for these general-use receptacle loads, the additional load to be added = Zero.

B- For branch circuit requirements (conductor ampacity & size and over-current protection) calculation

This will be explained in coming articles, however you can review the calculation for maximum number of allowable receptacles on a branch circuit and the minimum required number of branch circuits for a dwelling building which were discussed before in previous article 
" Receptacle Branch Circuit Design Calculations – Part Three ".

1.3 How to specify the required Type of general-use receptacles for each area?

1- Grounding type:

As per NEC section 406.4, Receptacles installed on 15- and 20-ampere branch circuits shall be of the grounding type.

2- GFCI type:

As per NEC section 210.8 (A), all 125-volt, single-phase, 15- and 20-ampere receptacles are GFCI for the following locations:

A- Bathrooms (see image below Rule#9)
There are no exceptions to the bathroom GFCI requirement. For example, if a washing machine is located in the bathroom, the 15- or 20-ampere, 125-volt receptacle that is required to be supplied from the laundry branch circuit must be GFCI protected.

B- Garages and accessory buildings (see below image)
It is the locations that have a floor located at or below grade level not intended as habitable rooms and limited to storage areas, work areas, and areas of similar use.

There are no exceptions to the GFCI requirements in Garages and accessory buildings, and this ensures that all 125-volt, single-phase, 15- and 20-ampere receptacles installed in garages are GFCI type regardless of where the receptacle is located in the garage.

C- Unfinished basements
Unfinished basements are defined as portions or areas of the basement not intended as habitable rooms and limited to storage areas, work areas, and the like.

All The receptacles in a work area of a basement, as shown in image below Rule#11, must be GFCI type. 

If the basement has some finished areas such as sleeping rooms or family rooms, then all receptacles in such areas will not required to be GFCI type as shown in image below Rule#11.

D- Crawl spaces
All receptacles installed in crawl spaces (at or below ground level) must be GFCI type.

E- Kitchens
I explained in above rule#5 that a general-use receptacle branch circuits must be added to kitchens to serve Receptacles installed for disposals, dishwashers, and trash compactors. These receptacles are not required to be GFCI type. The same is for receptacle(s) installed behind a refrigerator to supply that appliance, not the countertop, and will not be GFCI type.

F- Sinks located in areas other than kitchens (see below image)
All 125-volt, 15- and 20-ampere receptacles that are within 6 ft of any point along the outside edge of the sink located in areas other than kitchens is required to be GFCI type.

G- Outdoors
All outdoor receptacles are GFCI type with the condition that it is readily accessible. If it is not, it will be exempt from the GFCI requirements as shown in below image.

The dwelling unit shown has four outdoor receptacles, illustrates the requirement of 210.8(A) (3). The three receptacles with direct grade-level access must be provided with GFCI protection. The fourth receptacle, located adjacent to the gutter for the roof-mounted snow-melting cable, is not readily accessible and, therefore, is exempt from the GFCI requirements of 210.8(A)(3) because of its dedicated function to supply the deicing equipment.

H- Boathouses
Boathouse is A shed adjacent to a house at the edge of a river or lake used for housing boats.

3- Weatherproof type

As per NEC section 406.9, the weatherproof feature is allowed for the following locations: 

A- Damp locations 

All 15- and 20-ampere, 125- and 250-volt receptacles installed in a damp location shall have an enclosure that is weatherproof whether or not the attachment plug cap is inserted.

B- Wet locations
All 15- and 20-ampere, 125- and 250-volt receptacles installed in wet locations shall have an enclosure for the receptacle that is weatherproof.
A receptacle suitable for wet locations shall also be considered suitable for damp locations. 

Receptacle, located under roofed open porches, canopies, marquees, and the like, and will not be subjected to a beating rain or water runoff, shall be not weatherproof type.

the below image summarize the weatherproof features in all cases as per NEC section 406.9.

4- Tamper-Resistant type

Tamper-Resistant receptacles are intended to increase safety for children. All non-locking type 125- volt, 15- and 20-ampere receptacles shall be listed tamper resistant receptacles. the below image show the method of operation for 
Tamper-Resistant feature:

The Receptacles in the following locations shall not be required to be tamper-resistant:

  1. Receptacles located more than 1.7 m (51⁄2 ft) above the floor (these receptacles are not accessible and well out of reach of small children). 
  2. Receptacles that are part of a luminaire or appliance. 
  3. A single receptacle or a duplex receptacle located within dedicated space for appliance that, in normal use, is not easily moved from one place to another ( like dishwashers, refrigerators, washing machines, and the like ) 

5- AFCI type

All 15- and 20-ampere, 120-volt branch circuits that supply outlets including receptacle, lighting, and other outlets located throughout a dwelling unit family rooms, dining rooms, living rooms, parlors, libraries, dens, bedrooms, sunrooms, recreation rooms, closets, hallways, or similar rooms or areas shall be AFCI type.
Other outlets installed in kitchens, bathrooms, unfinished basements, garages, and outdoors will not be AFCI type. 

Please, note the following:
  • Shared circuits between a bedroom and other areas such as closets and hallways must have AFCI protection. 
  • There is no prohibition against using AFCI protection on other circuits or locations other than those specified in 210.12(A). 

The AFCI device to be located at the first outlet supplied by a branch circuit in the following cases:

  1. If the wiring method from the branch-circuit overcurrent protective device to the outlet is metallic conduit or tubing. 
  2. If the wiring method from the branch-circuit overcurrent protective device to the outlet is Nonmetallic conduit or tubing that is encased in not less than 2 inch of concrete. 

Another method for applying AFCI protection for branch circuit that require such protection is by installing A listed combination-type AFCI located at the origin of the branch circuit (in panelboard for example).

The following table will summarize the required receptacle type for each location in dwelling units:

Specifying a Receptacle in Dwelling Buildings
Receptacle Type
family rooms
dining rooms
living rooms
recreation rooms
kitchens, counter receptacles
kitchens, general-use receptacles
unfinished basements
Sinks located in areas other than kitchens
Crawl spaces
All 15- and 20-ampere, 125- and 250-volt receptacles installed in dwelling
unit are grounding and non-locking type.
All 15- and 20-ampere, 125- and 250-volt receptacles installed in a damp
 and Wet Locations are Weatherproof type (see exception above).
All non-locking type 125- volt, 15- and 20-ampere
 receptacles installed in dwelling units are Tamper-Resistant
 type (see exceptions above)
** in branch circuits that need AFCI protection only the first Receptacle will
 be AFCI type and other receptacles (on the same branch circuit) will be
normal type.

In the next article, I will explain Receptacle branch circuits that serve other types of loads. Please, keep following.

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