dwelling units - nec optional method calculation

8/17/2019 Dwelling Units - NEC Optional Method Calculation

1/40

NEC Optional calculation method is applicable o

FIRST: SINGLE-FAMILY DWELLING

!" per NEC ##$%#&!'NEC Optional calculation meth

+- Dwelling unit must be ser(ed by a single +#$#$-

#- 0he ser(ice-entrance or feeder conductors ha(e a

Note* 1f the ser(ice-entrance ampacity calculate

Step-1 : Calculating general lighting an gener

)r"ceure

Step-*: Calculating S&all-appliance +ranch circ

)r"ceure

!s per ##$%#&2', for dwelling units, minimumgeneral lighting and general-use receptaclesload is / 3!ft#

Calculate the 4oor area for each 4oor of DwellingUnit in ft#

Calculate the re5uired number of small-appliancebranch ciruits in the dwelling unit

!s per NEC section ##$%#&2'', each #-wiresmall-appliance branch circuit load is calculatedat no less than +,6$$ (olt-amperes


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Step-: Calculating Launr' +ranch ciruit l"a

)r"ceure

Step-.: Fa!tene in )lace Appliance! L"a

7ilo(olt-amperes &83!' shall be considered e5ui(

0he :astened-in-place !ppliances load, regardles

0he nameplate of the :astened-in-place !pplian

/ater heater

Re%rigerat"r

Free0er

Calculate the re5uired number of laundry branchciruits in the dwelling unit

!s per NEC ##$%#&2'', each #-wire laundry

branch circuit is calculated at no less than+,6$$ (olt-amperes

1f 0he fastened-in-place appliances ;oad includinfastened-in-place appliances, add the nameplat


3/40

i!h/a!her

i!p"!al

Range h""

&icr"/ae

&ini Re%rigerat"r

in!t h"t

ir"ning center

/ine Clr

A &"re Appliance!

A &"re Appliance!

A &"re Appliance!

T"ta

Step-4: Cl"the! Dr'er! L"a

! clothes dryer is not a re5uirement for a load ca

0he dryer load is not sub


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0he >ousehold coo8ing appliances load is not su

0he nameplate load of the >ousehold coo8ing a

=ange

9all-mounted o(en

Counter-mounted Coo8ing units

Step-9: M"t"r!

9hen calculating the feeder or ser(ice load of a

Do not include heating and air conditioning e5ui

1nclude only permanently connected motors that

Motor?+

Motor?#

Motor?/

Motor?

Step-: De&an "% General L"a

!s per NEC section ##$%#&2'&', add the namep

Bermanently connected motors must be added tof the motors may ha(e already been added to t

:or example, a 8itchen waste disposer could bealready been added to the load calculation as fa


5/40

Calculate the demand o

Calculate the de

Step-:6eating an air c"niti"ning l"a! #F;

!s per NEC section ##$%# &C', for >eating and

a- +$$ percent of the nameplate rating&s' of the

b- +$$ percent of the nameplate rating&s' of the

d- 6 percent of the nameplate rating&s' of elect

e- $ percent of the nameplate rating&s' of elect

f- +$$ percent of the nameplate ratings of electri

c- +$$ percent of the nameplate rating&s' of thepre(ented from operating at the same time as t

Ca!e


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)ut the Large!t L"

T;TAL DEMAND L;AD F

SEC;ND: SINGLE-FAMILY DWELLING

1f the total ser(ice load for a multifamily dwellin

+- 1f No dwelling unit is supplied by more than o

#- Each dwelling unit is e5uipped with electric c

/- Each dwelling unit is e5uipped with either ele

:or multifamily dwellings without electric coo8in+- Calculate the load of multifamily dwellings as

#- Calculate the load of multifamily dwellings as

6 percent of the nameplate rating&s' of electricspace heating

Ca!e

$ percent of the nameplate rating&s' of electricspace heating

Ca!e


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/- "elect the lowest load

Step-:6eating an air c"niti"ning l"a! #F"r

!s per NEC section ##$%, for Multifamily Dwelli

9ith the optional method multifamily dwelling lo

9ith the optional method multifamily dwelling lo

!ir Conditioni

"pace >eati

)ut the Large!t L

Step-@: 6"u!e L"a! #%"r Multi-Fa&il' D/elling


!s per ##$%&2', >ouse loads shall be calculate

!pplying the 0able ##$% demand factor to hou

T;TAL L;AD F;E

Step-1B: Appl'ing the Ta+le **B>. e&an %a

write the number of dwellin

from table ##$% , de

9ith a heat pump, the compressor &and accompsystem load K the maximum amount of heat tha

>eat pump ;oad A he air conditioning system loconditioner


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T;TAL DEMAND L;AD

T6IRD: TW;-FAMILY DWELLING

the total load of two-family dwelling as per NEC "tan

the total load of 0hree-family dwelling as per NEC Op

T;TAL DEMAND L;AD

F;RT6: EISTING DWELLING

0he purpose of doing ser(ice and feeder calcula

!s per NEC section ##$%, !dditional loads may

+- 0he maximum demand 83! data for a minimu

#- 0he maximum demand at +#6 percent plus th

/- 0he feeder has o(ercurrent protection in accoNO0E"*

:or condition?# in =ule?+ abo(e, apply the NEC

9here* Existing ;oad 3alue A Max demand 3alu

1f condition?# in =ule?+ abo(e is not (eri)ed, y

1n accordance with ##$%6, where two dwelling uwith NEC optional method, the lesser of the two

Berforming the optional method load calculationload calculation

:or condition?+ in =ule?+ abo(e, 1f the maximupower demand o(er a +6-minute period' continuser(ice, based on the initial loading at the startshall include by measurement or calculation the


9/40

Ca!e#A( : Where Aiti"nal Air-C"niti"nin

step?+* Existing ;oad 3alue in 3! as per NEC "tandr

if data are not a(ailable to ma8e calculation of this s

step?/* 0otal ;oad A Existing ;oad 3alue K New ;oa

step?* !pply ##$%/&!' demand factor for total ;oa

Calculate the demand

Calculate the de

Ca!e #( : Where Aiti"nal Air-C"niti"ning E

0he larger connected load of air-conditioning or spac

0he following percentages shall be used for exis

a' !ir-conditioning e5uipment at +$$

b' Central electric space heating at +$$

c' ;ess than four separately controlled space he

step?+* Existing ;oad 3alue in 3! as per NEC "tandr

if data are not a(ailable to ma8e calculation of this s

the calculation of electrical load as per NEC Opti

only dierence is the amount of load that is rate

step?+-optional* Existing ;oad 3alue in 3! as per NE##$%&+' x +#6 A

step?#* Calculate New ;oad as per NEC "tandard Me

A

additional loads for of air-conditioning or space-h

step?+-optional* Existing ;oad 3alue in 3! as per NE##$%&+' x +#6 A


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step?#* select the larger load from air-conditioning l

a' !ir-conditio

b' Central elect

c' ;ess than four separately

the larg

step?* 0otal ;oad A Existing ;oad 3alue K New ;oa

step?6* !pply ##$%/&!' demand factor for total ;oa

Calculate the demand

Calculate the de

step?/* Calculate New ;oad as per NEC "tandard Me A


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welling Units - NEC Optiona

ly for a single dwelling unit, an existing dwelling unit, a multif

d will be used if the following condition is (eri)ed*

(olt or #$%.+#$-(olt set of /-wire ser(ice or feeder conductors

ampacity of at least +$$ amperes

by the optional method is less than +$$!, re-calculate with u

l receptacle! l"a! #e$cept %"r !&all-appliance an Launr

N"te

uit!, l"a

N"te

Under any conditions, for dwelling units, donPt use (alue lessthan / 3!ft#, there are no exceptions 9hile the designercan choose a higher (alue based on the existing designconditions

0he 4oor area for each 4oor shall be calculated from theoutside dimensions of the dwelling unit

0he calculated 4oor area shall not include open porches,

garages, or unused or un)nished spaces not adaptable forfuture use &li8e some attics, cellars, and crawl spaces'

!s per NEC #+$+&C'&+', 1n each dwelling unit, two or more#$-ampere small-appliance branch circuits must be pro(ided

the designer assign the number of small-appliance branchciruits based on the exisiting condition &space dimension ,number of re5uired small appliances, etc'

DonQt exceed the permissible loading of a +#$ 3, #$- amperebranch circuit which is #$$ 3!


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N"te

alent to 8ilowatts &89'

s of the number, will not be derated as re5uired per NEC secti

es that are fastened in place, permanently connected or locat

Nu&+er "% appliance!

!s per NEC #+$++&C'', 1n each dwelling unit, !t least one#$-ampere branch circuit shall be pro(ided

g water heater is gi(en, do not include water heat load to therating of the water heater to the general loads co(ered in ##


13/40

l"a in #2A( 3

lculation, "8ip this step if there is no clothes dryer

and factor as re5uired by table ##$6 for NEC "tandard calc

e(en if it is less than 6$$$ watts


N"te

T"tal l"a "% cl"the! r'er! 3

! combination of clothes washer and clothes dryer will behandled in calculations as it is a clothes dryer


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b


15/40

f 0he :irst +$,$$$ 3! or ;ess at +$$

and of =eminder, if any, at $

De&an "% General L"a in #2A( 3

Single -Fa&il' /elling "nl'(

ir-Conditioning ;oad, 0he largest of the following six selection

air conditioning and cooling

heat pump when the heat pump is used without any supplem

ic space heating if less than four separately controlled units

ic space heating if four or more separately controlled units

c thermal storage &E0"' and other heating systems where the

Nameplate=ating

heat pump compressor and 6 percent of the supplemental ele supplementary heat, it does not need to be added to the su


16/40

%r"& that "% !i$ ca!e! a+"e

;E SINGLE- FAMILY DWELLING 3

is 8nown, and there is a re5uirement to supply the building b

e feeder

o8ing e5uipment

tric space heating or air conditioning, or both

range &using gas coo8ing ranges or other and may use electper NEC standard method

per NEC optional method with adding electric coo8ing &based

s, multiple ser(ices and feeders may be installed to supply p

not the same as the number on the ser(ice, it will be necessa

method, for a multifamily dwelling, 0able ##$% GOptional Ca

ded all of the conditions for using table ##$% listed abo(e a


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L"a %r"& Step-1 t" Step-9 in #2A( 3

Multi-Fa&il' /elling "nl'(

ng, the demand factors of 0able ##$% shall be applied to th

ad calculation, the air conditioning load is calculated at +$$

ad calculation, the load for space heating units must be adde

g ;oad Nameplate =ating A

g Unit Nameplate =ating A

a %r"& the #( L"a! a+"e

"nl'(


in accordance with NEC "tandard method

e loads of multifamily dwellings is not permitted >ouse loads

6"u!e L"a in #2A( 3

LTI- FAMILY DWELLING 3

t"r %"r Multi-%a&il' /elling

units in a multifamily dwelling building A

termine the Demand :actor (alue A

nying motors' and some or all of the electric heat can be ent can be on while the air conditioner compressor is energiJed

d K the maximum amount of heat that can be on while the aircompressor is energiJed


18/40

;E MLTI- FAMILY DWELLING 3

ard Method A

tional Method for Multifamily dwelling A

F;E TW;- FAMILY DWELLING 3

ions for an existing dwelling unit is to determine if the existin

be connected to existing ser(ices and feeders under the follo

m +-year period &or the /$-day alternati(e method from the e

e new load does not exceed the ampacity of the feeder or rati

dance with #$, and the ser(ice has o(erload protection in

standard Calculation method to get the total load as follows*

for a +-year period from ##$%&+' x +#6 , New ;oad A Con

u need to increase ampacity of the feeder andor rating of th

nits are supplied by a single feeder and the calculated load aoads shall be permitted

for two dwelling units without performing the standard metho

demand data for a +-year period is not a(ailable, the calculously recorded o(er a minimum /$-day period using a recordif the recording 0he recording shall re4ect the maximum demlarger of the heating or cooling e5uipment load, and other loa


19/40

E=uip&ent "r Electric Space-6eating E=uip&ent I! N"

method A

ep, then apply step?+-optional

A

f 0he :irst %,$$$ 3! or ;ess at +$$


De&an T"tal L"a in %"r E$i!ting D/elling nit - Ca!e #A(

uip&ent "r Electric Space-6eating E=uip&ent I! t" e In!ta

-heating, but not both, shall be used

ing and additional new loads*

ting units at +$$

method A

ep, then apply step?+-optional

nal Calculation Method :or !n Existing Dwelling Unit Case &

at +$$ percent, in ##$%#&2' for single family dwelling it was

"tandrd method A Max demand 3alue for a +-year period from

thod A Continuous loads x +#6 K Non-continuous loads x +$$

eating, so the following will be applied for these loads*

"tandrd method A Max demand 3alue for a +-year period from


20/40

ad , central electric space heating and less than four separately co

ing e5uipment at +$$ A

ic space heating at +$$ A

ontrolled space heating units at +$$ A

r load from a, b, c A

A

f 0he :irst %,$$$ 3! or ;ess at +$$


De&an T"tal L"a in %"r E$i!ting D/elling nit - Ca!e #(

thod A Continuous loads x +#6 K Non-continuous loads x +$$


21/40

l Method Calculation

amily dwelling, two dwelling units, a school, an existing installation and

sing the standard method

Receptacle!(

Calculati"n

:loor area in ft# A $

General lighting an general receptacle! l"a! 3 $

Calculati"n

Number of "mall-appliance branch circuits in the dwelling unit A $

0he general lighting load is calculated by multiplying the 4oor area &inunit by / 3!ft#

0he "mall-appliance branch circuitsP load, for dwelling units, is calculatenumber of "mall-appliance branch circuits by +,6$$ 3!

!s per #+$6#&2'&+'Exception#, !n ind(idual branch ciruit is permitted for =eat +,6$$ 3! 1f you will apply this rule,choose Number of =efergiator Circuits fr


22/40

S&all-appliance +ranch circuit!, l"a 3 $

Calculati"n

Number of ;aundry branch circuits in the dwelling unit A $

Launr' +ranch circuit!, l"a 3 $

on ##$6/

ed to be on a speci)c circuit will be used &E(en 1f less than 6$$$ 9att3

Na&eplate Rating "% appliance!

0he ;aundry branch circuitsP load, for dwelling units, is calculated by mu;aundry branch circuits by +,6$$ 3!

! combination of clothes washer and clothes dryer will be handled in caclothes dryer, is there a combinationR "elect answer from :##

general load as per ##$%#&2'&/'d 2ut if the water heater was not incl%#&2'


23/40

ulation method

Calculati"n

9rite the Nameplate =ating of Cothes dryer $

Number of Clothes Dryers A $

$


24/40

66 for NEC "tandard calculation method

used

Nameplate =ating

oad current of permanently connected motors by +#6 percent

connected motors that are supplied by house power

Nameplate =ating

ntly connected motors to the general loads co(ered in ##$%#&2' 1nclu

calculated by the NEC optional method !lthough motors are listed sep

pliance or as a permanently connected motor 1t is not necessary to ad


25/40

demand of 0he :irst /,$$$ 3! or ;ess A

demand of & +#$,$$$ 3! - /,$$$ 3!', if any A

&load in 83!' shall be included*

ntal electric heating

usual load is expected to be continuous at the full nameplate (alue

supplemental electric heat nameplate rating &case?/'

ectric heating for central electric space-heating systems 1f the heat pupplementary heat for the total central space heating load


26/40

$

$

y multiple feeders, do not


27/40

larger of the air-conditioning load or the )xed electric space-heating lo

of the nameplate rating

to the calculation at the nameplate rating

Nameplate =ating

$

$

$

must be calculated as per NEC standard method

$

rgiJed at the same time "o, 0he load contribution of a heat pump A th


28/40

$

3!

3!

$

ser(ice or feeder is of suLcient capacity to ser(e a re5uired additional

wing conditions*

ception' is a(ailable

ng of the ser(ice

ccordance with #/$$

otal ;oad A Existing ;oad 3alue K New ;oad

tinuous loads x +#6 K Non-continuous loads x +$$

ser(ice to be able to add new loads to an existing dwelling unit

per NEC standard method exceeds that for three identical units calcula

load calculation is permissible, but the result could be larger than the

ted load shall be permitted to be based on the maximum demand &meg ammeter or power meter connected to the highest loaded phase of t

and of the feeder or ser(ice by being ta8en when the building or spaceds that may be periodic in nature due to seasonal or similar conditions


29/40

t t" e In!talle>

3!

3!

3!

3!

demand of 0he :irst %,$$$ 3! or ;ess A

demand of & +#$,$$$ 3! - /,$$$ 3!', if any A

in #2A( 3

lle>

3!

3!

' is almost identical to the calculation method in ##$%#&2' for single f

+$ 73! but in ##$%/ for existing dwelling it will be % 73!


30/40

trolled space heating units

3!

3!

3!

3!

3!

$3!

demand of 0he :irst %,$$$ 3! or ;ess A

demand of & +#$,$$$ 3! - /,$$$ 3!', if any A

in #2A( 3


31/40

a new restaurant

ft#

3!

$ $

+

Ciruit #

t#' of a dwelling

by multiplying

rigeration e5uipmentom :+/


32/40

3! /

N .

Ciruit $ N

3!

'

$

$

$

ltiplying number of

lculations as it is a

ded with the


33/40

$

$

$

$

$

$

$

$

$

$

$

$

3!

3!


34/40

$

$

$

$

$

$

$

$

$

$

$

$

e all motors that

arately, some or all

motors that ha(e


35/40

$

$

$

$

$

$

p compressor is


36/40

$

$

$

3!

2A

number of feeders

sary to perform

itsI will be used if

ed by using


37/40

B

ad

3!

$

2A

air conditioning


38/40

2A

2A

loads or not

ted in accordance

standard method

sure of a(eragehe feeder oris occupied and


39/40

$

$

$

mily dwelling 0he


40/40

$

$

$

dwelling units - nec optional method calculation

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