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, TwoFamily, MultiFamily 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, twofamily and multifamily.
 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: SINGLEFAMILY 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 120/240volt or
208Y/120volt set of 3wire service or feeder conductors


2 The serviceentrance or feeder conductors have an ampacity of
at least 100 amperes.


Note: If the serviceentrance ampacity
calculated by the optional method is less than 100A, recalculate with using
the standard method.


Step1 : Calculating general lighting and general receptacles
loads (except for smallappliance and Laundry Receptacles)


Procedure

Note

Calculation


As per 220.82(B), for dwelling units, minimum
general lighting and generaluse 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


Step2: Calculating Smallappliance branch circuits’ load


Procedure

Note

Calculation


Calculate the required number of smallappliance branch ciruits
in the dwelling unit

As per NEC 210.1(C)(1), In each dwelling unit,
two or more 20ampere smallappliance branch circuits must be provided.

The Smallappliance branch
circuits’ load, for dwelling units, is calculated by multiplying number of Smallappliance branch
circuits by 1,500 VA.


the designer assign the number of
smallappliance 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 2wire
smallappliance branch circuit load is calculated at no less than 1,500
voltamperes.

Number of Smallappliance branch circuits in the dwelling unit =

0

Ciruit


Smallappliance branch circuits’ load =

0

VA


Step3: 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 20ampere 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 2wire laundry
branch circuit is calculated at no less than 1,500 voltamperes.


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


Step4: Fastened in Place Appliances Load


If The fastenedinplace 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 fastenedinplace appliances, add the nameplate rating of the water
heater to the general loads covered in 220.82(B).


Kilovoltamperes (kVA) shall be considered
equivalent to kilowatts (kW)


The Fastenedinplace Appliances load,
regardless of the number, will not be derated as required per NEC section
220.53.


The nameplate of the Fastenedinplace
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


Step5: 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.


Kilovoltamperes (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


Step6: Household cooking appliances load


Kilovoltamperes (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


Wallmounted oven

0


Countermounted Cooking units

0


0


0


Household cooking appliances
load in KW=

0


Step7: 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
fastenedinplace appliances.


For example, a kitchen waste disposer could be
added to an optional load calculation as a fastenedinplace appliance or as a
permanently connected motor. It is not necessary to add motors that have
already been added to the load calculation as fastenedinplace appliances.


When calculating the feeder or service load of
a dwelling unit by the optional method, do not multiply the fullload 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


Step8: 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


Step8:Heating and air conditioning loads (FOR Single Family
dwelling only)


As per NEC section 220.82 (C), for Heating and
AirConditioning 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 spaceheating 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 spaceheating 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: SINGLEFAMILY 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 Step1 to Step7 in (VA) =

0


Step8:Heating and air conditioning loads (For MultiFamily
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 airconditioning load or the fixed electric spaceheating 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


Step9: House Loads (for MultiFamily Dwelling only)


Kilovoltamperes (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


Step10: Applying the Table 220.84 demand factor for
Multifamily 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: TWOFAMILY 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 twofamily dwelling as per NEC Standard Method
=

VA


the total load of Threefamily 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
1year period (or the 30day 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 1year period is not available, the calculated load
shall be permitted to be based on the maximum demand (measure of average
power demand over a 15minute period) continuously recorded over a minimum
30day 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 1year period from 220.87(1) x 125% , New Load = Continuous loads x 125
% + Noncontinuous 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 AirConditioning
Equipment or Electric SpaceHeating 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#1optional


step#1optional: Existing Load Value in VA as per NEC Standrd
method = Max demand Value for a 1year period from 220.87(1) x 125% =

VA


step#2: Calculate New Load as per NEC Standard Method = Continuous
loads x 125 % + Noncontinuous 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 AirConditioning Equipment or
Electric SpaceHeating 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 airconditioning or spaceheating, so the
following will be applied for these loads:


The larger connected load of airconditioning or spaceheating,
but not both, shall be used.


The following percentages shall be used for
existing and additional new loads:


a) Airconditioning 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#1optional


step#1optional: Existing Load Value in VA as per NEC Standrd method
= Max demand Value for a 1year period from 220.87(1) x 125% =

VA


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


a) Airconditioning 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 % +
Noncontinuous 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

Free Download
to download your copy of Electrical Load Calculator for Dwelling Units as per NEC Optional Method, just click on the link.
In the next Article I will explain the electrical load calculation for nondwelling buildings as per NEC code. Please, keep following.
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