Receptacle Branch Circuit Design Calculations – Part Seven


In article " Receptacle Branch Circuit Design Calculations – Part Three ", 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. Cloth dryer Load, 
  5. Household cooking appliances load, 
  6. Fastened-in-place Appliance loads, 
  7. Heating and air conditioning loads, 
  8. Motor loads. 

I explained the first four types in the following articles: 



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


You can review the following articles for more information: 




5- Household cooking appliances load


Definition:
Cooking Unit, Counter-Mounted is a cooking appliance designed for mounting in or on a counter and consisting of one or more heating elements, internal wiring, and built-in or mountable controls.(see below image)



  • Wall-mounted ovens and counter-mounted cooking units complete shall be permitted to be permanently connected or, only for ease in servicing or for installation, cord-and-plug-connected. 
  • A portable cooking appliance (e.g., cord-and-plug-connected microwave oven or hot plate) is not a permanent cooking facility. 

5.1 Applied NEC Rules for Household cooking appliances load


There are many NEC rules that control the location and load of Household cooking appliances including:

  • NEC section 220.53 
  • 210.18 Guest Rooms and Guest Suites - dwelling units 
  • 210.19 (A) (3) Minimum Ampacity and Size of conductors for Branch Circuits Not More Than 600 Volts supplying Household Ranges and Cooking Appliances 
  • 210.50 General (C) Appliance Receptacle Outlets 
  • 210.52(B) Small Appliances (2) No Other Outlets Exception No. 2 
  • 210.23 Permissible Loads (C) 40- and 50-Ampere Branch Circuits 
  • 220.55 Electric Ranges and Other Cooking Appliances — Dwelling Unit(s) 

 
Rule#1: Location of receptacle outlet used for Electric Ranges

Appliance receptacle outlets installed in a dwelling unit for specific appliances, such as laundry equipment, shall be installed within 1.8 m (6 ft) of the intended location of the appliance.

Receptacle outlets for Wall-mounted ovens and counter-mounted cooking units shall be located on or above, but not more than 500 mm (20 in.) above, the countertop.



Rule#2: Guest Rooms and Guest Suites in dwelling units and that are provided with permanent provisions for cooking(see below image)

Guest rooms and guest suites that are provided with permanent provisions for cooking shall have branch circuits installed in the cooking area to meet the all of the requirements for dwelling units contained in Parts I, II, and III of Article 210.





Important!!!
A portable cooking appliance (e.g., cord-and-plug-connected microwave oven or hot plate) is not a permanent cooking facility.



Rule#3: Not Fastened-in-Place Appliances

As per NEC section 220.53, electric ranges, clothes dryers, space-heating equipment or air conditioning equipment must not be included with the number of appliances that are fastened in place.
Also, All portable small Appliances for kitchen and others are not Fastened-in-Place Appliances.



Rule#4: Supplying Supplemental equipment and lighting

Receptacle outlets of small appliance branch circuits are permitted to serve Supplemental equipment and lighting on gas-fired ranges, ovens, or counter-mounted cooking units.



Important!!!
In most dwellings the countertop receptacle outlets supply more of the portable cooking appliances than the wall receptacles in the kitchen and dining areas, hence the requirement for the counter areas to be supplied by no fewer than two small-appliance branch circuits.




5.2 Calculation of Household Cooking Appliances load


A- For feeder and service calculation purposes


First: As per NEC Standard calculation method



Rule#5: Code Requirement for Household Cooking Appliances

Household Cooking Appliances (ranges, wall mounted ovens, counter-mounted cooking appliances, etc.) are not required in a NEC load calculation. We can skip the calculation of Household Cooking Appliances Load if there are no cooking appliances rated over 1.75 KW.



Important!!!
Kilovolt-amperes (kVA) shall be considered equivalent to kilowatts (kW) for Electric Ranges and Other Cooking Appliances.



Important!!!
When the kilowatt rating fraction is 0.5 or more, it must be rounded up to the next whole kilowatt rating i.e.  14.5 KW up to a 15 KW and When the fraction is less than 0.5, it can be dropped i.e. 14.4 KW dropped to 14 KW.



Rule#6: calculating household cooking appliances load in accordance with Table 220.55.

As per NEC section 220.55, The load for household electric ranges, wall-mounted ovens, counter-mounted cooking units, and other household cooking appliances individually rated in excess of 1.75 kW shall be permitted to be calculated in accordance with Table 220.55.




Important!!!
The table 220.55 is not applicable for ranges rated more than 27 kW because ranges rated more than 27 kW would not be considered household ranges.


We have (5) cases for using table 220.55 as follows: 


Case#1: Individual Appliance not over 12 KW


The service load for one household cooking appliance is permitted to be computed by using either the nameplate rating of the appliance or Table 220.55.
In this case, Procedure for calculating the service demand load will be as follows: 


Step#1: Look in Left column of Table 220.55 for the number of appliances = 1

Step#2: Follow the row (for number of appliances = 1) across to the appropriate column A, B or C.
  • Column A is used where the rating of the appliance is less than 3½ kW 
  • Column B is used where the rating of the appliance is 3½ kW through 8¾ Kw 
  • Column C is used where the rating of the appliance not over 12-kW. 

Step#3: Service demand load calculation

  • If Column A or B is used, Service demand load = Load of the Individual Appliance x Demand factor 
  • If Column C is used, Service demand load = Max. Demand Load in column C 


Example#1:

12-kW electric range will be installed in a one-family dwelling, what is the service demand load for this range?


Solution:



Step#1: Look in the left column of Table 220.55 for the number of appliances=1.

Step#2: Follow the row across to the appropriate column which will be Column C

Step#3: In accordance with Column C, a 12-kW range has a maximum demand of 8 kW



Example#2:

What is the service demand load for a 9-kW range?


Solution:

Step#1: Look in the left column of Table 220.55 for the number of appliances=1.

Step#2: Follow the row across to the appropriate column which will be Column C

Step#3: In accordance with Column C, The maximum load required for one 9-kW range when calculating a service or feeder is 8 kW.



Example#3:


What is the service demand load for a 3-kW, wall-mounted oven?


Solution:



Step#1:
Look in the left column of Table 220.55 for the number of appliances=1.

Step#2: Follow the row across to the appropriate column which will be Column A

Step#3: In accordance with Column A, The demand factor percent = 80%

So, the service demand Load= 3 KW X 0.8 = 2.4 KW



Case#2: group of Appliances with equal (same) ratings not over 12 KW

The procedure is the same as in case#1 for individual Appliance as follows: 

Step#1: Look in Left column of Table 220.55 for the number of appliances, 

Step#2: Follow the row (for number of appliances given) across to the appropriate column A, B or C.

  • Column A is used where the rating of the appliances (have same rating) is less than 3½ kW. 
  • Column B is used where the rating of the appliances (have same rating) is 3½ kW through 8¾ KW 
  • Column C is used where the rating of the appliances (have same rating) is not over 12-kW. 

Step#3: Service demand load calculation

  • If Column A or B is used, Service demand load = Number of Appliances x Load of Individual appliance x Demand factor 
  • If Column C is used, Service demand load = Max. Demand Load in column C 


Example#4:

A 10-unit apartment building will have a 12-kW range in each apartment. What is the service demand load these ranges?


Solution: 




Step#1: Look in the left column of Table 220.55 for the number of appliances=10.

Step#2: Follow the row across to the appropriate column which will be Column C

Step#3: In accordance with Column C, for the number of appliances=10, the maximum service demand will be 25 kW



Example#5:


What is the service demand load for 40 wall-mounted ovens with same 3-kW rating?

Solution: 




Step#1: Look in the left column of Table 220.55 for the number of appliances=25.

Step#2: Follow the row across to the appropriate column which will be Column A

Step#3: In accordance with Column A, The demand factor percent = 30%
So, the service demand Load= Number of Appliances x Load of Individual appliance x Demand factor = 25 x 3 KW X 0.3 = 22.5 KW 



Example#6:


What is the service demand load for 40 ranges with same 10-kW rating?


Solution: 




Step#1: Look in the left column of Table 220.55 for the number of appliances=40.

Step#2: Follow the row across to the appropriate column which will be Column C

Step#3: In accordance with Column C, for the number of appliances=40, the maximum service demand will be 15 kW + 1 kW for each range.
So, the maximum service demand = 15 kW + number of appliances = 15 + 40 = 55 KW 



Example#7:

What is the service demand load for 60 ranges with same 12-kW rating? 


Solution: 




Step#1: Look in the left column of Table 220.55 for the number of appliances=60.

Step#2: Follow the row across to the appropriate column which will be Column C

Step#3: In accordance with Column C, for the number of appliances=60, the maximum service demand will be 15 kW + 0.75 kW for each range.

So, the maximum service demand = 25 kW + number of appliances X 0.75 KW = 25+ 60 X 0.75 = 70 KW



Case#3: group of Appliances with unequal ratings not over 12 KW

The procedure is the same as in case#2 for individual Appliance but Steps#1, 2 and 3 will be repeated for each Appliance as follows:

Step#1: Look in Left column of Table 220.55 for the number of appliances,

Step#2: Follow the row (for number of appliances given) across to the appropriate column A, B or C.

  • Column A is used where the rating of the appliances (have same rating) is less than 3½ kW. 
  • Column B is used where the rating of the appliances (have same rating) is 3½ kW through 8¾ KW 
  • Column C is used where the rating of the appliances (have same rating) is not over 12-kW. 

Step#3: Service demand load calculation

  • If Column A or B is used, Service demand load = Number of Appliances x Load of Individual appliance x Demand factor 
  • If Column C is used, Service demand load = Max. Demand Load in column C 

Step#4: Sum individual service demand loads to get the total service demand load.



Example#8:

What is the service demand load for ten 2.5-kW ovens, ten 3-kW ovens, ten 5-kW cooktops and ten 6-kW cooktops? 


Solution: 

First: for 20 units that are within the limits of Column A 


Step#1:The 2.5-kW ovens have a rating = 10 × 2½ = 25 KW.

The 3-kW ovens have a rating = 10 × 3 = 30KW.

The ovens have a total rating = 25 + 30 = 55 KW

Step#2: Because 20 ovens fall within the limits of Column A, the demand factor is 35 %.

Step#3: The calculated demand for the ovens = 55 × 35% = 19.25 KW 


Second: for 20 units that are within the limits of Column B


Step#1: The 5-kW cooktops have a rating = 10 × 5 = 50 KW

The 6-kW cooktops have a rating = 10 × 6 = 60 KW

The cooktops have a total rating = 50 + 60 = 110 KW

Step#2: Because 20 ovens fall within the limits of Column B, the demand factor is 28 %.

Step#3: The calculated demand for the cooktops = 110 × 28% = 30.8 KW 


Step#4: Now add the results to find the total demand load = 19.25 + 30.8 = 50.05 KW


Example#9:

What is the service demand load for five 3.5-kW wall-mounted ovens, five 5-kW counter-mounted cooking units and ten 8-kW ranges? 


Solution:
Step#1: the total number of units (5 + 5 + 10 = 20).

Step#2: Because none of the appliances are rated less than 3½ kW or more than 8¾ kW, the demand factor will come from Column B.

So, the demand factor percent across from 20 units (28 percent).

Step#3:

The ovens have a total rating of 17½ kW = 5 × 3.5 = 17.5KW

The cooktops have total rating of 25 kW = 5 × 5 = 25 KW

The ranges have a total rating of 80 kW = 10 × 8 = 80 KW

Step#4:

The combined rating of all the appliances = 17.5 + 25 + 80 = 122.5 KW

The service demand load = 122.5 KW × 28% = 34.3 KW



Optional Calculation for Cases# 2 and 3 and appliances ratings Over 1 3 ⁄4 kW through 8 3⁄4 kW 


If appliances Ratings falling under Column A or B and C (ratings Over 1 3 ⁄4 kW through 8 3⁄4 kW), the calculation procedure will be as follows: 


Step#1: Calculate the service demand Load for such appliances whether falling under Column A or B

Step#2: Calculate the same using Column C,

Step#3: Choose the lowest value between steps# 1 and 2 to be the service demand Load.



Example#10:


What is the service demand load for 6 ranges with same 8-kW rating?


Solution: 


Using the optional method for household cooking appliances with ratings Over 1 3 ⁄4 kW through 8 3⁄4 kW

Step#1: Calculate the service demand Load for such appliances whether falling under Column A or B

In accordance with column B, the demand factor for 6 nos. appliances is 43% , so the service demand load = 6 x 8 x 0.43 = 20.64 KW

Step#2: Calculate the same using Column C,

In accordance with column C, for 6 nos. appliances, the Max. demand load = 21 KW

Step#3: Choose the lowest value between steps# 1 and 2 to be the service demand Load.

So, the service demand Load = the lowest value between steps# 1 and 2 = 20.64 KW



Case#4: Individual / group of Ranges with equal (same) ratings Over 12 kW through 27 KW


For ranges individually rated more than 12 kW but not more than 27 kW, the calculation procedure will be as follows: 


Step#1: Calculate the maximum demand for the given number of ranges in Column C. 

Step#2: Find the KW Load increase over 12 KW = KW of one range – 12

Step#3: Find the increased demand amount = Step#1 x Step#2 x 0.05

Step#4: Total service demand load= step#1 +step#3



Example#11:

What is the service demand load for one 14-kW household electric range? 


Solution:
Step#1: the maximum demand for one ranges in Column C = 8 KW 

Step#2: Load increase over 12 KW = 14 – 12 = 2 KW

Step#3: the increased demand amount = Step#1 x Step#2 x 0.05 = 8x2x0.05 = 0.8 KW

Step#4: Total service demand load= step#1 +step#3 = 8 + 0.8 = 8.8 kW



Case#5: group of Ranges with unequal ratings Over 8 3⁄4 kW through 27 kW

For ranges individually rated more than 8 3⁄4 kW and of different ratings, but none exceeding 27 kW, the calculation procedure will be as follows: 


Step#1: Calculate the maximum demand for the given number of ranges in Column C. 

Step#2: Calculate the Average Rating = sum of all appliances rating (using 12 kW for any range rated less than 12 kW) / number of appliances

Step#3: Find the KW Load increase over 12 KW = average load KW – 12

Step#4:
Find the increased demand amount = Step#1 x Step#3 x 0.05

Step#5: Total service demand load= step#1 +step#4



Example#12:

What is the service demand load for five 13-kW, five 15-kW and five 17-kW household electric ranges? 


Solution: 

Step#1: the maximum demand for 15 ranges in Column C = 30 KW 

Step#2: the Average Rating = [(5 × 13) + (5 × 15) + (5 × 17) / 15 = 15 KW

Step#3: Load increase over 12 KW = 15 – 12 = 3 KW

Step#4: the increased demand amount = Step#1 x Step#3 x 0.05 = 30x3x0.05 = 4.5 KW

Step#5: Total service demand load= step#1 +step#3 = 30 + 4.5 = 34.5 kW



Example#13:
What is the service demand load for eight 9-kW, six 13-kW and six 15-kW household electric ranges? 


Solution:

Step#1: the maximum demand for 20 ranges in Column C = 35 KW

Step#2: the Average Rating = [(8 × 12) + (6× 13) + (6 × 15) / 20 = 13.2 KW

Notes:
  • Use 12 kW for any range rated less than 12 kW 
  • 13.2 KW will be dropped to 13 KW 

Step#3: Load increase over 12 KW = 13 – 12 = 1 KW

Step#4: the increased demand amount = Step#1 x Step#3 x 0.05 = 35x1x0.05 = 1.75 KW

Step#5: Total service demand load= step#1 +step#3 = 35 + 1.75 = 36.75 kW



Second: As per NEC Optional calculation method:


Rule#7: Application of NEC Optional calculation method

NEC Optional calculation method will be used if the following condition is verified:
  1. The service-entrance or feeder conductors have an ampacity of at least 100 amperes.




Important!!!
If the service-entrance ampacity calculated by the optional method is less than 100A, re-calculate with using the standard method.



Important!!!
In NEC Optional calculation method, for a multifamily dwelling, Table 220.84 “Optional Calculations — Demand Factors for Three or More Multifamily Dwelling Units” will be used if the following conditions are verified:
  1. If No dwelling unit is supplied by more than one feeder
  2. Each dwelling unit is equipped with electric cooking equipment.
  3. Each dwelling unit is equipped with either electric space heating or air conditioning, or both.




Rule#8: For multifamily dwellings without electric cooking Range

For multifamily dwellings without electric cooking range (using gas cooking ranges or other and may use electrical range in future) do the following:
  1. Calculate the load of multifamily dwellings as per NEC standard method
  2. Calculate the load of multifamily dwellings as per NEC optional method with adding electric cooking (based on 8 kW per unit)
  3. Select the lowest load.




Important!!!
The optional calculation can be used, provided all of the conditions for using table 220.84 listed above are met. Otherwise, the calculation for the multifamily dwelling is performed by using standard calculation method.


Rule#9: Calculation of Household cooking appliances as per NEC optional method

In Optional calculation method, note the following:
  1. The Household cooking appliances load is not subject to an individual demand factor as required by table 220.55 for NEC Standard calculation method.
  2. The nameplate load of the Household cooking appliances (fastened in place or permanently connected) will be used.




Example#14:


A multifamily dwelling has 20 dwelling units, One-half of the dwelling units are equipped with electric ranges not exceeding 12 kW each and other half of ranges are gas ranges. What is the service demand load for these ranges?


Solution: 

1- Calculated Load for Each Dwelling Unit 

In accordance with column C in table 220.55, Max. demand load for One Electric range = 8KW


2- Calculate the service demand load 


Step#1: Look in the left column of Table 220.55 for the number of appliances=10.

Step#2: Follow the row across to the appropriate column which will be Column C

Step#3: The maximum service demand load = 25 KW




B- For branch circuit requirements calculation


1- Determining Branch-Circuit Load


Important!!!
The branch-circuit load for one household cooking appliance is permitted to be computed by using either the nameplate rating of the appliance or Table 220.55.



Important!!!
Where counter-mounted cooking appliances like the one pictured in below image are used with a separate wall oven, it is permissible to run a single branch circuit, sized according to Note 4 to Table 220.55, to the kitchen and supply each with branch-circuit tap conductors installed as specified in 210.19(A)(3), Exception No. 1.




Important!!!
If a single branch circuit supplies a counter-mounted cooking unit and not more than two wall-mounted ovens, all of which are located in the same room, the nameplate ratings of these appliances can be added and the total treated as the equivalent of one range, according to Note 4 of Table 220.55.



Rule#10: Circuit ratings for Electric Ranges

High-wattage cord-and-plug-connected loads, such as electric ranges, clothes dryers, and some window air conditioners, may be connected to a 208-volt or 240-volt 3 phase, 4 wire circuit.
Same can be done by using single phase multi-wire circuits that can supply both line-to-line and line-to-neutral connected loads as in below image.




Important!!!
Where two or more single-phase ranges are supplied by a 3-phase, 4-wire feeder or service, the total load shall be calculated on the basis of twice the maximum number connected between any two phases.



Rule#11: household cooking appliances branch circuit rating

As per 210.19(A)(3) Branch circuit conductors supplying household ranges, wall-mounted ovens, counter-mounted cooking units, and other household cooking appliances shall have an ampacity not less than the rating of the branch circuit and not less than the maximum load to be served. For ranges of 8 3⁄4 kW or more rating, the minimum branch-circuit rating shall be 40 amperes.

the permissible rating For Wall-mounted ovens and counter-mounted cooking units to be connected to 15- and 20-Ampere Branch Circuits is as follows:
  1. If it is not fastened-in-place, it can have a rating of up to 80 % of the branch circuit rating as in TABLE 210.21(B)(2).
  2. If it is fastened-in-place, other than luminaires, it shall not exceed 50 % of the branch-circuit ampere rating.




Important!!!
Exception to Rule#9, Conductors tapped from a 50-ampere branch circuit supplying electric ranges, wall-mounted electric ovens, and counter-mounted electric cooking units shall have an ampacity of not less than 20 amperes and shall be sufficient for the load to be served.  As illustrated in fig. , this exception permits a 20-ampere tap  if the following four conditions are met:

  1. The taps are not longer than necessary to service or permit access to the junction box.
  2. The taps to each unit are properly spliced.
  3. The junction box is adjacent to each unit.
  4. The taps are of sufficient size for the load to be served.



Household cooking appliances branch circuit conductor ampacity & size and over-current protection will be explained in coming articles, however you can review the calculation for maximum number of allowable receptacles on a branch circuit which was discussed before in previous article " Receptacle Branch Circuit Design Calculations – Part Three "



5.4 How to specify the required Type and Rating of receptacles for household cooking appliances?

A- Range Receptacle Rating


The ampere rating of a range receptacle shall be permitted to be based on a single range demand load as specified in Table 220.55.


B- GFCI Type

As I explained in Rule#4 that a Receptacle outlet connected to small appliance branch circuits is permitted to serve Supplemental equipment and lighting on gas-fired ranges, ovens, or counter-mounted cooking units.

As per NEC section 210.8 A (6), where the receptacles are installed to serve the countertop kitchen appliances (counter-mounted cooking units) around a kitchen sink must be GFCI Type. See below image.



But the receptacle serves Supplemental equipment and lighting on gas-fired ranges and ovens will not be GFCI type as in above image.
According to 406.5(E), receptacles installed to serve countertops cannot be installed in the countertop in the face-up position because liquid, dirt, and other foreign material can enter the receptacle 


C- Tamper-Resistant type


Tamper-Resistant receptacles are intended to increase safety for children.

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

  • 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). 
  • 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 ).



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



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