Electrical Load Calculator for Dwelling Units


I explained Where and how to distribute each type of load in a dwelling unit as per NEC code. Also I explained how to calculate the Demand load for each type of dwelling loads for feeder and service sizing calculations in the following Articles:





Today, I introduce to you, the most professional Excel Sheet for calculating the Total Demand Load for single, Two-Family, Multi-Family Dwelling Units as per NEC Standard Calculation Method.


This excel Sheet is exclusive for our website Electrical Know how, You will not find this Professional excel sheet anywhere in the web.






the benefits of using this sheet than other similar ones are as follows:


  • it explains all the NEC rules applied for each calculation step inside the sheet.
  • It is the most applicable calculator for all types of dwelling units; single, two-family and multi-family.
  • It is the easy one for understanding and application.
  • Some Demand Factors Tables are included in the excel sheet and no need to manually extract its data from the code as other similar ones do.



I put the excel sheet in a word format in below just for easy reviewing for each step calculations, rules, exceptions and tables.

for download the spreadsheet click on the link in below of the word format.



Dwelling Units - NEC Standard Method Calculation
Note: If a dwelling has more than one feeder, a separate load calculation is needed for each feeder.

Step-1 : Calculating general lighting and general receptacles loads (except for small-appliance and Laundry Receptacles)
Procedure
Note
Calculation
From NEC Table 220.12, for dwelling units, minimum general lighting load is 3 VA/ft2.
Under any conditions, for dwelling units, don’t use value less than 3 VA/ft2, there are no exceptions. While the designer can choose a higher value based on the existing design conditions
The general lighting load is calculated by
 multiplying the floor area (in ft2) of a
 dwelling unit by 3 VA/ft2.
Calculate the floor area for each floor of Dwelling Unit in ft2.
The floor area for each floor shall be calculated from the outside dimensions of the dwelling unit.
Floor area in ft2 =
0
ft2
The calculated floor area shall not include open porches, garages, or unused or unfinished spaces not adaptable for future use (like some attics, cellars, and crawl spaces).

General lighting and general receptacles loads =
0
VA
Step-2: Calculating Small-appliance branch circuits’ load
Procedure
Note
Calculation
Calculate the required number of small-appliance branch ciruits in the dwelling unit
As per NEC 210.1(C)(1), In each dwelling unit, two or more 20-ampere small-appliance branch circuits must be provided.
The Small-appliance branch circuits’ load, for dwelling units, is calculated by multiplying number of Small-appliance branch circuits by 1,500 VA.
the designer assign the number of small-appliance branch ciruits based on the exisiting condition (space dimension , number of required small appliances, etc.).
As per 210.52(B)(1)Exception.2, An indvidual branch ciruit is permitted for Refrigeration equipment at 1,500 VA. If you will apply this rule,choose Number of Refergiator Circuits from F13
2
Don't exceed the permissible  loading of a 120 V, 20- ampere branch circuit which is 2400 VA
If a dwelling has more than one feeder, a
 separate load calculation is needed for 
each feeder. It is not necessary to 
include small-appliance branch circuit 
loads for feeders don’t supply such load.
 Does feeder include small-appliance 
branch circuits?Select answer from  F14

N
As per NEC section 220.52(A), each 2-wire small-appliance branch circuit load is calculated at no less than 1,500 volt-amperes.

Number of Small-appliance branch circuits in the dwelling unit =
0
Ciruit
0


Small-appliance branch circuits’ load =
0
VA
0
Step-3: Calculating Laundry branch ciruit load
Procedure
Note
Calculation
Calculate the required number of laundry branch ciruits in the dwelling unit
As per NEC 210.11(C)(2), In each dwelling unit, At least one 20-ampere branch circuit shall be provided
The Laundry branch circuits’ load, for dwelling units, is calculated by multiplying number of Laundry branch circuits by 1,500 VA.
As per NEC 220.52(B), each 2-wire laundry branch circuit is calculated at no less than 1,500 volt-amperes.

In multifamily dwelling building, if Laundry facilities are provided on the premises and available to all building tenants (as a common usage), Laundry branch circuits load will not be added to each individual dwelling unit and will be added to a separate “house load” panelboard. is Laundry Facility available to all building tenants?Select answer from  F21
N


A combination of clothes washer and clothes dryer will be handled in calculations as it is a clothes dryer, is there a combination? Select answer from  F22
Y


Number of Laundry branch circuits in the dwelling unit =
1
Ciruit
1


Laundry branch circuits’ load =
0
VA
Step-4: Applying Demand Factors from Table 220.42

Sum Loads of Step-1, Step-2 and Step-3
Total Sum =
0
VA
Calculate the demand of The First 3,000 VA or Less at 100%
demand of The First 3,000 VA or Less =
0
VA
Calculate the demand of ( 120,000 VA - 3,000 VA), if any, at 35%
demand of ( 120,000 VA - 3,000 VA), if any =
0
VA
Calculate the demand of the reminder over 120,000 VA, if any, at 25%
demand of the reminder over 120,000 VA, if any =
0
VA


General Load for Lighting, General Receptacles, Small Appliances and Laundry =
0
VA
Step-5: Fastened in Place Appliances Load
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.
Kilovolt-amperes (kVA) shall be considered equivalent to kilowatts (kW)
As per NEC section, 220.53, It shall be permissible to apply a demand factor of 75 % to the nameplate rating load of four or more appliances fastened-in-place,  that are served by the same feeder or service in a one-family, two-family, or multifamily dwelling.
In a multifamily dwelling, the four or more fastened-in-place appliances do not have to be on the same feeder for each dwelling unit. In this case, the 75% demand factor will not apply to the feeder for each dwelling unit but it must be applied to the multifamily dwelling service.
As per NEC section 430.6(A)(1), Do not use the actual current rating marked on the nameplate. When calculating motor loads, use the values given in Tables 430.247 through 430.250.


Number of appliances
Rating of appliances


water heater




Refrigerator




Freezer




dishwasher




disposal




Range hood




microwave




mini Refrigerator




inst hot




ironing center




wine Clr




Add more Appliances




Add more Appliances




Add more Appliances




total number of appliances =
0


Total ratings of appliances
0


Total load =
0
VA
Step-6: Clothes Dryers Load
A clothes dryer is not a requirement for a load calculation, Skip this step if there is no clothes dryer.
Kilovolt-amperes (kVA) shall be considered equivalent to kilowatts (kW)
Procedure
Note
Calculation
Write the Nameplate Rating of  Cothes dryer
As per NEC section 220.54, the load for household electric clothes dryers in a dwelling unit(s) shall be either 5000 watts (volt-amperes) or the nameplate rating, whichever is larger, for each dryer served.
Write the Nameplate Rating of  Cothes dryer
0
VA

A combination of clothes washer and clothes dryer (see below image) will be handled in calculations as it is a clothes dryer.
5000 VA or the nameplate rating, whichever is larger
5000
VA

For single, two-family or multi-family dwelling when each tenant has separate clothes dryer, Table 220.54 Demand Factors for Household Electric Clothes Dryers will be used
Number of Clothes Dryers =
0


In a multi-family dwelling where there is a common Laundry area, use the full load of all dryers without applying demand factor.
Total Conneced load of clothes dryers =
0
VA
0
0
0
0
0
0
0
0
0
0
0



0
0
Demand Factor =
0

Total Demand load of clothes dryers =
0
VA
Step-7: Household cooking appliances load
We can skip the calculation of Household Cooking Appliances Load if there are no cooking appliances rated over 1.75 KW.
Kilovolt-amperes (kVA) shall be considered equivalent to kilowatts (kW)
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.
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.

Case#1: Individual Appliance
Household cooking appliances Rating in KW=
0



Less that 3.5 KW Rating
3.5-8.5 KW
less than 12 KW
12KW<rating<27KW


0
0
0
0
Household cooking appliances Demand load in KW=
0


Case#2: group of Appliances with equal (same) ratings not over 12 KW
Number of Household cooking appliances =
0




Household cooking appliances Rating in KW=
0






Put Demand/max. Demand Factor from table 220.55
Calculated demand load


Less that 3.5 KW Rating

0
0

3.5-8.5 KW

0
0

less than 12 KW

0

Household cooking appliances Demand load in KW=
0


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

group Rating #1
group Rating #2
group Rating #3

Number of Household cooking appliances =




Household cooking appliances Rating in KW=




IF Less that 3.5 KW Rating, D.F =




IF from 3.5 to 8.5 KW, D.F=




IF less than 12 KW, Max. Demand =




Calculated demand load
0
0
0


0
0
0

Household cooking appliances Demand load in KW=
0


Case#4: group of Ranges with equal (same) ratings Over 12 kW through 27 KW
Number of Household cooking appliances =





Household cooking appliances Rating in KW=

Put Demand/max. Demand Factor from table 220.55
Calculated demand load




0

Household cooking appliances Demand load in KW=
0


Case#5: group of Ranges with unequal ratings Over 8 3⁄4 kW through 27 kW
total Number of Household cooking appliances =





Max. Demand from Column C, Table 220.55=






Ranges Rating over 12 KW
Ranges Rating Below 12 KW


Number of Household cooking appliances =




Sum of Household cooking appliances Rating in KW=




the Average Rating =
#DIV/0!




Household cooking appliances Demand load in KW=
#DIV/0!
Step-8:Heating and air conditioning loads
the blower motor works with both the heating and air conditioning system, it must be included in both calculations.
With a heat pump, the compressor (and accompanying motors) and some or all of the electric heat can be on at the same time. The load contribution of a heat pump is the air conditioning system load plus the maximum amount of heat that can be on while the air conditioner compressor is on.
As per NEC section 430.6(A)(1), Do not use the actual current rating marked on the nameplate. When calculating motor loads, use the values given in Tables 430.247 through 430.250.

Noncoincident Loads
coincident Loads
Room air conditioners Load in VA at 100%

FALSE

Fixed electric space-heating Load in VA at 100%

FALSE

Central air conditioning Load in VA at 100%

FALSE

Central heating system Load in VA at 100%

FALSE





Heating and air conditioning load in VA =
0
0
Step-9: The Largest Motor
As per NEC section 430.6(A)(1), Do not use the actual current rating marked on the nameplate. When calculating motor loads, use the values given in Tables 430.247 through 430.250.
Exceptions to 430.6(A)(1) :
1- Motors built for low speeds (less than 1,200 rpm) or high torques for multispeed motors.
2- For equipment that employs a shaded-pole or permanent-split capacitor-type fan or blower motor that is marked with the motor type, use the full load current for such motor marked on the nameplate of the equipment in which the fan or blower motor is employed.
3- For a listed motor-operated appliance that is marked with both motor horsepower and full-load current, use the motor full-load current marked on the nameplate of the appliance.
When calculating a feeder or service As per NEC Standard calculation method, the largest motor must be multiplied by 25 percent and add it to the service load calculation.
If the motor is air conditioning compressor, usually the air conditioning compressor is the largest motor in dwelling units. in this case, multiply the load of one compressor by 25 percent and add it to the service load calculation. But if the heating load is larger than the air conditioning load, and because of 220.60 which states that” it is permissible to use only the larger of the noncoincident loads” the air conditioning load will be omitted and the air conditioning compressor will not be the largest motor in this case.

VA of Largest Motor =




Largest Motor Additional Load =
0
VA


TOTAL DEMAND LOAD =
#DIV/0!
VA






Free Download

to download your copy of Electrical Load Calculator for Dwelling Units as per NEC Standard Method, just click on the link.




in the next Article I will introduce Electrical Load Calculator for Dwelling Units as per NEC Optional Method. please, keep following.


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