Optional Electrical Load Calculator for Dwelling Units


I explained in Article " Electrical Load Calculator for Dwelling Units " the steps of calculating electrical load for any dwelling unit as per NEC standard calculation method. 

Also, 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, and Existing Dwelling as per NEC Optional 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.


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



Dwelling Units - NEC Optional Method Calculation
NEC Optional calculation method is applicable only for a single dwelling unit, an existing dwelling unit, a multifamily dwelling, two dwelling units, a school, an existing installation and a new restaurant.
FIRST: SINGLE-FAMILY DWELLING
AS per NEC 220.82(A)NEC Optional calculation method will be used if the following condition is verified:
1- Dwelling unit must be served by a single 120/240-volt or 208Y/120-volt set of 3-wire service or feeder conductors
2- The service-entrance or feeder conductors have an ampacity of at least 100 amperes.
Note: If the service-entrance ampacity calculated by the optional method is less than 100A, re-calculate with using the standard method.
Step-1 : Calculating general lighting and general receptacles loads (except for small-appliance and Laundry Receptacles)
Procedure
Note
Calculation
As per 220.82(B), for dwelling units, minimum general lighting and general-use receptacles 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
0
Don't exceed the permissible  loading of a 120 V, 20- ampere branch circuit which is 2400 VA

As per NEC section 220.82(B)(2), 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


Small-appliance branch circuits’ load =
0
VA
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 220.82(B)(2), each 2-wire laundry branch circuit is calculated at no less than 1,500 volt-amperes.




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
N


Number of Laundry branch circuits in the dwelling unit =
0
Ciruit
0


Laundry branch circuits’ load =
0
VA
Step-4: Fastened in Place Appliances Load
If The fastened-in-place appliances Load including water heater is given, do not include water heat load to the general load as per 220.82(B)(3)d . But if the water heater was not included with the fastened-in-place appliances, add the nameplate rating of the water heater to the general loads covered in 220.82(B).
Kilovolt-amperes (kVA) shall be considered equivalent to kilowatts (kW)
The Fastened-in-place Appliances load, regardless of the number, will not be derated as required per NEC section 220.53.
The nameplate of the Fastened-in-place Appliances that are fastened in place, permanently connected or located to be on a specific circuit will be used (Even If less than 5000 Watt/VA).


Number of appliances
Nameplate Rating of appliances

water heater


0
Refrigerator


0
Freezer


0
dishwasher


0
disposal


0
Range hood


0
microwave


0
mini Refrigerator


0
inst hot


0
ironing center


0
wine Clr


0
Add more Appliances


0
Add more Appliances


0
Add more Appliances


0
Total load in (VA) =

0
Step-5: Clothes Dryers Load
A clothes dryer is not a requirement for a load calculation, Skip this step if there is no clothes dryer.
The dryer load is not subject to an individual demand factor as required by table 220.54 for NEC Standard calculation method.
The nameplate of the clothes dryer will be used, even if it is less than 5000 watts.




Kilovolt-amperes (kVA) shall be considered equivalent to kilowatts (kW)
Procedure
Note
Calculation
Write the Nameplate Rating of  Cothes dryer
A combination of clothes washer and clothes dryer will be handled in calculations as it is a clothes dryer.
Write the Nameplate Rating of  Cothes dryer
0
VA

Number of Clothes Dryers =
0



Total load of clothes dryers =
0
VA
Step-6: Household cooking appliances load
Kilovolt-amperes (kVA) shall be considered equivalent to kilowatts (kW)
The Household cooking appliances load is not subject to an individual demand factor as required by table 220.55 for NEC Standard calculation method.
The nameplate load of the Household cooking appliances (fastened in place or permanently connected) will be used.

number
Nameplate Rating

Range


0
Wall-mounted oven


0
Counter-mounted Cooking units


0



0



0

Household cooking appliances  load in KW=
0





Step-7:  Motors
As per NEC section 220.82(B)(4), add the nameplate ampere (A) or kilovolt ampere (kVA) rating of all permanently connected motors to the general loads covered in 220.82(B). Include all motors that are not already included with the general loads covered in 220.82(B)
Permanently connected motors must be added to the general loads when calculating a feeder or service when calculated by the NEC optional method. Although motors are listed separately, some or all of the motors may have already been added to the load calculation as fastened-in-place appliances.
For example, a kitchen waste disposer could be added to an optional load calculation as a fastened-in-place appliance or as a permanently connected motor. It is not necessary to add motors that have already been added to the load calculation as fastened-in-place appliances.
When calculating the feeder or service load of a dwelling unit by the optional method, do not multiply the full-load current of permanently connected motors by 125 percent
Do not include heating and air conditioning equipment in the list with permanently connected motors.
Include only permanently connected motors that are supplied from dwelling units. Do not include permanently connected motors that are supplied by house power.

Number
Nameplate Rating

Motor#1


0
Motor#2


0
Motor#3


0
Motor#4


0

Motors Load in (VA) =
0





Step-8: Demand of General Load

General Load =
0
Calculate the demand of The First 10,000 VA or Less at 100%
demand of The First 3,000 VA or Less =
0
Calculate the demand of Reminder, if any, at 40%
demand of ( 120,000 VA - 3,000 VA), if any =
0


Demand of General Load in (VA) =
0
Step-8:Heating and air conditioning loads (FOR Single -Family dwelling only)

As per NEC section 220.82 (C), for Heating and Air-Conditioning Load, The largest of the following six selections (load in kVA) shall be included:
a- 100 percent of the nameplate rating(s) of the air conditioning and cooling.
b- 100 percent of the nameplate rating(s) of the heat pump when the heat pump is used without any supplemental electric heating.
c- 100 percent of the nameplate rating(s) of the heat pump compressor and 65 percent of the supplemental electric heating for central electric space-heating systems. If the heat pump compressor is prevented from operating at the same time as the supplementary heat, it does not need to be added to the supplementary heat for the total central space heating load.
d- 65 percent of the nameplate rating(s) of electric space heating if less than four separately controlled units.
e- 40 percent of the nameplate rating(s) of electric space heating if four or more separately controlled units.
f- 100 percent of the nameplate ratings of electric thermal storage (ETS) and other heating systems where the usual load is expected to be continuous at the full nameplate value.






NameplateRating
supplemental electric heat nameplate rating (case#3)

Case#1: If a dwelling has some type of heat other than electric



the air conditioning load only at 100 percent of the nameplate rating


0
Case #2: Heat pumps equipped with or without electric supplemental heat.



Heat pumps not equipped with supplemental electric heat  at 100 percent of the nameplate rating


0
Case #3: When a heat pump is used with supplemental electric heat,



multiply the nameplate rating(s) of the heat pump compressor by 100 percent and multiply the supplemental electric heating for central electric space-heating systems by 65 percent.


0
Case#4: electric space heating by less than four separately controlled units.



65 percent of the nameplate rating(s) of electric space heating


0
Case#5: electric space heating by four or more separately controlled units.



40 percent of the nameplate rating(s) of electric space heating


0
Case#6:  using electric thermal storage (ETS) and other heat systems



100 percent of the nameplate ratings of electric thermal storage (ETS) and other heat systems where the usual load is expected to be continuous at the full nameplate value.


0

Put the Largest Load from that of six cases above
0
VA

TOTAL DEMAND LOAD FOE SINGLE- FAMILY DWELLING =
0
VA

SECOND: SINGLE-FAMILY DWELLING
Sometimes, in large multifamily dwelling buildings, multiple services and feeders may be installed to supply power to different floors or different buildings; in this case, it will be necessary to perform optional load calculation for each feeder.
Generally, if the number of units on the feeder is not the same as the number on the service, it will be necessary to perform more than one load calculation.
If the total service load for a multifamily dwelling is known, and there is a requirement to supply the building by multiple feeders, do not just divide the service load calculation by the number of feeders.
As per NEC 20.84(A), 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.
Note: 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.
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.
Load from Step-1 to Step-7 in (VA) =
0
Step-8:Heating and air conditioning loads (For Multi-Family dwelling only)
As per NEC section 220.84, for Multifamily Dwelling, the demand factors of Table 220.84 shall be applied to the larger of the air-conditioning load or the fixed electric space-heating load.
With the optional method multifamily dwelling load calculation, the air conditioning load is calculated at 100 % of the nameplate rating.
With the optional method multifamily dwelling load calculation, the load for space heating units must be added to the calculation at the nameplate rating.
With a heat pump, the compressor (and accompanying motors) and some or all of the electric heat can be energized at the same time. So, The load contribution of a heat pump = the air conditioning system load + the maximum amount of heat that can be on while the air conditioner compressor is energized.

Nameplate Rating

Air Conditioning Load Nameplate Rating =
0
Space Heating Unit Nameplate Rating =
0
Heat pump Load = he air conditioning system load + the maximum amount of heat that can be on while the air conditioner compressor is energized.
0

Put the Largest Load from the (3) Loads above

VA
Step-9: House Loads (for Multi-Family Dwelling only)
Kilovolt-amperes (kVA) shall be considered equivalent to kilowatts (kW)
As per 220.84(B), House loads shall be calculated in accordance with NEC Standard method
Applying the Table 220.84 demand factor to house loads of multifamily dwellings is not permitted. House loads must be calculated as per NEC standard method.

House Load in (VA) =
0

TOTAL  LOAD FOE MULTI- FAMILY DWELLING =
0
VA
Step-10: Applying the Table 220.84 demand factor for Multi-family dwelling
write the number of dwelling units in a multifamily dwelling building =


from table 220.84 , determine the Demand Factor value =

TOTAL DEMAND LOAD FOE MULTI- FAMILY DWELLING =
0
VA
THIRD: TWO-FAMILY DWELLING
In accordance with 220.85, where two dwelling units are supplied by a single feeder and the calculated load as per NEC standard method exceeds that for three identical units calculated in accordance with NEC optional method, the lesser of the two loads shall be permitted.
Performing the optional method load calculation for two dwelling units without performing the standard method load calculation is permissible, but the result could be larger than the standard method load calculation.
the total load of two-family dwelling as per NEC Standard Method =

VA
the total load of Three-family dwelling as per NEC Optional Method for Multifamily dwelling =

VA

TOTAL DEMAND LOAD FOE TWO- FAMILY DWELLING =
0
VA
FORTH: EXISTING DWELLING
The purpose of doing service and feeder calculations for an existing dwelling unit is to determine if the existing service or feeder is of sufficient capacity to serve a required additional loads or not.
As per NEC section 220.87, Additional loads may be connected to existing services and feeders under the following conditions:
1- The maximum demand kVA data for a minimum 1-year period (or the 30-day alternative method from the exception) is available.
2- The maximum demand at 125 percent plus the new load does not exceed the ampacity of the feeder or rating of the service.
3- The feeder has overcurrent protection in accordance with 240.4, and the service has overload protection in accordance with 230.90.
NOTES:
For condition#1 in Rule#1 above, If the maximum demand data for a 1-year period is not available, the calculated load shall be permitted to be based on the maximum demand (measure of average power demand over a 15-minute period) continuously recorded over a minimum 30-day period using a recording ammeter or power meter connected to the highest loaded phase of the feeder or service, based on the initial loading at the start of the recording. The recording shall reflect the maximum demand of the feeder or service by being taken when the building or space is occupied and shall include by measurement or calculation the larger of the heating or cooling equipment load, and other loads that may be periodic in nature due to seasonal or similar conditions.
For condition#2 in Rule#1 above, apply the NEC standard Calculation method to get the total load as follows: Total Load = Existing Load Value + New Load
Where: Existing Load Value = Max demand Value for a 1-year period from 220.87(1) x 125% , New Load = Continuous loads x 125 % +  Non-continuous loads x 100 %
If condition#2 in Rule#1 above is not verified, you need to increase ampacity of the feeder and/or rating of the service to be able to add new loads to an existing dwelling unit.
Case(A) : Where Additional Air-Conditioning Equipment or Electric Space-Heating Equipment Is Not to Be Installed.
the calculation of electrical load as per NEC Optional Calculation Method For An Existing Dwelling Unit – Case (A) is almost identical to the calculation method in 220.82(B) for single family dwelling. The only difference is the amount of load that is rated at 100 percent, in 220.82(B) for single family dwelling it was 10 KVA but in 220.83 for existing dwelling it will be 8 KVA.
step#1: Existing Load Value in VA as per NEC Standrd method =

VA

if data are not available to make calculation of this step, then apply step#1-optional
step#1-optional: Existing Load Value in VA as per NEC Standrd method = Max demand Value for a 1-year period from 220.87(1) x 125% =

VA

step#2: Calculate New Load as per NEC Standard Method = Continuous loads x 125 % +  Non-continuous loads x 100 % =

VA

step#3: Total Load = Existing Load Value + New Load =

VA

step#4: Apply 220.83(A) demand factor for total Load


Calculate the demand of The First 8,000 VA or Less at 100%
demand of The First 8,000 VA or Less =
0
Calculate the demand of Reminder, if any, at 40%
demand of ( 120,000 VA - 3,000 VA), if any =
0

Demand Total Load in for Existing Dwelling Unit - Case (A) in (VA) =
0
Case (B) : Where Additional Air-Conditioning Equipment or Electric Space-Heating Equipment Is to Be Installed.
Calculation of electrical load as per NEC Optional Calculation Method For An Existing Dwelling Unit – Case (B), In this case, the calculation is identical to that of case (A), But In this case, there are additional loads for of air-conditioning or space-heating, so the following will be applied for these loads:
The larger connected load of air-conditioning or space-heating, but not both, shall be used.
The following percentages shall be used for existing and additional new loads:
a) Air-conditioning equipment at  100%
b) Central electric space heating at %100
c) Less than four separately controlled space heating units at 100%
step#1: Existing Load Value in VA as per NEC Standrd method =

VA

if data are not available to make calculation of this step, then apply step#1-optional
step#1-optional: Existing Load Value in VA as per NEC Standrd method = Max demand Value for a 1-year period from 220.87(1) x 125% =

VA

step#2: select the larger load from air-conditioning load , central electric space heating and less than four separately controlled space heating units

a) Air-conditioning equipment at  100% =

VA

b) Central electric space heating at %100 =

VA

c) Less than four separately controlled space heating units at 100% =

VA

the larger load from a, b, c =

VA

step#3: Calculate New Load as per NEC Standard Method = Continuous loads x 125 % +  Non-continuous loads x 100 % =

VA

step#4: Total Load = Existing Load Value + New Load =
0
VA

step#5: Apply 220.83(A) demand factor for total Load


Calculate the demand of The First 8,000 VA or Less at 100%
demand of The First 8,000 VA or Less =
0
Calculate the demand of Reminder, if any, at 40%
demand of ( 120,000 VA - 3,000 VA), if any =
0

Demand Total Load in for Existing Dwelling Unit - Case (B) in (VA) =
0




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In the next Article I will explain the electrical load calculation for non-dwelling buildings as per NEC code. Please, keep following.



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