Branch Circuit Design Calculations – Part Eight


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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 five 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: 




6- Fastened-in-place Appliances branch circuits



Definition:
The term appliance designates utilization equipment commonly built in standardized types and sizes and installed as a unit to perform specific function(S) such as clothes washing, air conditioning, food mixing, deep frying, etc.

Some examples of appliances that are fastened in place whether direct wired or cord and plug connected include dishwashers, kitchen-waste disposers, trash compactors, attic fans and water heaters (see below image).






Definitions:
  • Appliance, Fixed is An appliance that is fastened or otherwise secured at a specific location.
  • Appliance, Portable is An appliance that is actually moved or can easily be moved from one place to another in normal use.
  • Appliance, Stationary is An appliance that is not easily moved from one place to another in normal use.




Rule#1: Not Fastened-in-Place Appliances (see below image)

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#2: Location of receptacle outlet used for Electric Appliances

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.



Important!!!
The load for an appliance is simply the ampere rating of that appliance which may be indicated on its nameplate and will be used in branch, feeder and service load calculations.




6.1 Applied NEC Rules for Fastened-in-place Appliances load


There are many NEC rules that control the location and load of Fastened-in-place appliances including: 

  • 210.23(A) Permissible Loads for 15- and 20-Ampere Branch Circuits 
  • 220.14 (A) Specific Appliances or Loads in All Occupancies 
  • 220.53 Appliance Load in Dwelling Unit 
  • 220.82(B)(3) Optional Feeder and Service Load Calculations of General Loads in Dwelling Unit 



6.2 Calculation of Fastened-in-place Appliances load


A- For feeder and service calculation purposes


First: As per NEC Standard calculation method: 




Important!!!
Kilovolt-amperes (kVA) shall be considered equivalent to kilowatts (kW) for Fastened-in-place Appliances.



Rule#3: Calculation of Fastened-in-place Appliances load

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.



Important!!!
No derating is allowed when there are only one, two, three fastened-in-place appliances.



Example#1:

A one-family dwelling will have two feeders supplied by the service. One feeder will provide power to a water heater and two attic ventilation fans. The other feeder will provide power to a dishwasher, a kitchen-waste disposer and a trash compactor. Where the 75 % demand factor to be applied? 


Solution: 


Since only three appliances are on each feeder, it is not permissible to apply the 75 % demand factor to either feeder load calculation.

The demand factor can be applied to the service load calculation because it will supply power to six fastened-in-place appliances.



Example#2:

What is the appliance load contribution, for a house that has a 1.2 KVA dishwasher, a 0.76 KVA garbage disposer, a 1.1 KVA trash compactor and a 4.5 KVA water heater? 


Solution: 


Step#1: find the total load or the Fastened-in-place Appliances

Total load = 1.2+0.76+1.1+4.5 = 7.56 KVA
Step#2: if the number of the Fastened-in-place Appliances is four or more, apply the 75% demand factor. 

Demand load = 7.56 x 75% = 5.67 KVA




Rule#4: Calculation of Fastened-in-place Appliances load For 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.



Example#3:


A 4.5-kilowatt (kW), 240-volt (V) water heater will be installed in each unit of a four-unit multifamily dwelling. The water heaters are the only fastened-in-place appliance in this multifamily dwelling. One service will supply all four units. Using the standard method, what is the service load (after applying the demand factor) for fastened-in-place appliances? 


Solution: 


Each unit has only one fastened-in-place appliance, the 75% demand factor will not apply to the feeder for each dwelling unit.

But there will be four fastened-in-place appliances on the multifamily dwelling service. Therefore, applying the 75 percent demand factor is permissible.

The service load for these water heaters = 4x4.5x0.75 = 13.5 KW 



Second: As per NEC Optional calculation method:



Rule#5: 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.




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#6: Calculation of Fastened-in-place Appliances load as per NEC Optional calculation method

In Optional calculation method, note the following:
  1. The Fastened-in-place Appliances load, regardless of the number, will not be derated as required per NEC section 220.53.
  2. 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.




Important!!!
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).


Example#4:

what is the optional method service load calculation for a one-family dwelling with the following fastened-in-place appliances: a dishwasher rated 10 amperes (A) at 120 volts (V); a horsepower, 120V kitchen waste disposer; a trash compactor rated 7.5A at 120V; and a 4.5 kilowatts (kW), 240V water heater?


Solution: 


The loads in KVA will be as follows:

The dishwasher load = 10A x120V = 1,200 VA = 1.2 KVA

Kitchen waste disposer load = 9.8A x 120V = 1,176 VA = 1.176 KVA

The compactor load = 7.5A x 120V = 900 VA = 0.9 KVA

The water heater load = 4,500W = 4,500 VA = 4.5 KVA

The optional method service load = 1.2 + 1.176 + 0.9 + 4.5 = 7.776 KVA



Example#5:


Find the optional method service load calculation for a 12-unit multifamily dwelling with each unit containing the following fastened-in-place appliances: a dishwasher rated 10 amperes (A) at 120V; 9.8 A, 120V kitchen waste disposer, and a 4.5 kW, 240V water heater.


Solution: 

The loads in KVA will be as follows: 

The dishwasher load = 10A x 120V = 1,200 VA.

The kitchen waste disposer load = 9.8A x 120V = 1,176 VA.

Water heater load = 4.5 KW x1,000 = 4,500 W = 4500 VA

The fastened-in-place appliance load for each unit = 1,200 + 1,176 + 4,500 = 6,876 VA


Since there are 12 units, multiply the appliance load by 12

The fastened-in-place appliance service load for the building = 12 x 6,876 VA = 82,512 VA


Apply the Table 220.84  (in below image) for demand factor, of Multifamily dwelling, since there are 12 units, the demand factor will be 41%.

The optional method demand load for this building = 82,512 VA x 41% = 33,830 VA





B- For branch circuit requirements (conductor ampacity & size and over-current protection) calculation




Rule#7: Combination of Fastened-in-place Appliances with other loads on a branch circuit

As per NEC section 210.23(A), The total rating of utilization equipment fastened in place, other than luminaires, shall not exceed 50 percent of the 15- and 20-Ampere Branch Circuits branch-circuit rating where lighting units, cord-and-plug-connected utilization equipment not fastened in place, or both, are also supplied.



Rule#8: Rating of Fastened-in-place Appliances Outlet

As per NEC section 220.14 (A), an outlet for a specific appliance or other load not covered in 220.14(B) through (L) shall be calculated based on the ampere rating of the appliance or load served.



Example#6:


What is the branch-circuit load for a 10-ampere, 120-volt dishwasher in a dwelling?


Solution: 


Since the rating on the nameplate is 10 amperes, the branch-circuit load for this dishwasher is 10 amperes. 



Important!!!
Using fastened-in-place equipment is not permitted for the small-appliance branch circuits, laundry branch circuits, and bathroom branch circuits required in a dwelling unit and these branch circuits shall supply only their receptacle outlets required by the code.



Important!!!
Small loads, such as those of 1440 volt-amperes or less and motors of less than 1⁄4 horsepower, are limited to 120- volt circuits.




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





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