Single Family Dwelling load calculations

Example 1

This single family dwelling has a floor area of 2500 sq. ft. The appliances are a 10.5 KW range, 4.5 KW, 240 volt dryer, one 6 amp 115 volt garbage disposal, and one 12 amp dishwasher. What is the minimum size aluminum conductors feeding this dwelling?

Index: Loads. Feeders, Calculations = Annex D

  1. Go to annex D in your code book for reference. Example D1(a)
  2. Using your calculator multiply 2500 x 3 = 7500
  3. Small appliance load = 3000
  4. Laundry load = 1500
  5. Using your calculator add 7500, 3000, 1500 = 12000 now subtract 3000 = 9000 now multiply by .35 = 3150 now add 3000 = 6150
  6. This dwelling General load is 6150 VA

Explanation.

  • Every dwelling has a minimum Lighting load based on Area x Amount in table 220.12 (which is 3).
  • Every dwelling has a minimum Small appliance load of 3000 VA (article 220.52).
  • Every dwelling has a minimum Laundry load of 1500 VA (article 220.52).
  • Now go to Table 220.42 demand factors. Look at Dwelling Units. Using your calculator you can quickly find the net general load using #5 above.
  • You have to practice this to wrap your head around it, but you just add them all up subtract 3000 multiply by .35 then add the 3000 back in.

Okay you have your Net Load written down on the scratch paper the testing facility has provided. Now what?

  • Add in loads that have their own demand factor tables. Dryers and Ranges

Look at the question is your Range KW less than 12? Then you will use 8000 watts. Table 220.55

  1. Use 8000 VA for the range.

 We have 1-4 dryers here so we use 100% of the VA. Table 220.54 but read article 220.54. It says the minimum dryer load is 5000 VA

  1. Use 5000 VA for the dryer.

Back to the calculation.

  • General net load = 6150
  • Range = 8000
  • Dryer = 5000

Total calculated load. 6150 + 8000 + 5000 = 19,150 VA

What should you do about the additional motors? How do we add them to are total load?

  • Add any small motors using article 430.24. For testing this means take an extra 25% of the largest motor and add it to your Total load per line.
  • Here is the thing. We have been using VA in are calculations and finding demand factors. Now the question is giving us some nameplate ratings to add into are total.
  • If you look at Example D1(b) you will see the chart that shows Line A and Line B
  • If we calculate total load from above at 19,150 VA / 240 volt = 79.79 Amps = 80 Amps Per Line
  • If you add both devices 6 amps and 12 amps plus 25% the largest motor (12 x .25 = 3 amps) you get 21 amps. If you add this to only one line entering the dwelling it will be 101 amps on line A and 80 amps on line B. We are trying to balance the loads here and we are allowed to put one device on line A and one on line B. Being the largest motors on that line you will have to add 25% to the largest motor loads per line. giving us 80 +12+3 = 95 amps on Line A and 80 + 6 + 1.5 = 87.5 or 88 amps on Line B.
  • That said the service will be rated 100 Amps
  • The conductors will be #1 Aluminum (no termination rating was given and were talking 100 amps so you must use the 75% column.
  • Answer #1 ALU

Example 2

A single family dwelling has 5000 sq. ft. livable space a 2500 sq. ft. unfinished basement and a 4 stall garage. The appliance load includes a 12 KW range, a 12 KW double oven, 20 amp Sub Zero refrigerator, 15 amp trash compactor, two 8 amp garbage disposals, 30 amp warmer drawer, 5.5 kw dryer, 40 amp steam shower, 50 amp Hot Tub, 7.5 amp pool pump and two a 30 amp condensing units. What size service and conductors will be needed for this dwelling?

to be continued..

 


Service Feeders for a 8 unit 4 story Brownstone. Each Unit is 700 Sq Ft.

Residence Panel includes the following.

Oven   12 KW

A/C  

Heater 12 KW

Water Heater 5 KW

Laundry

Dryer 5 KW

Disposal

Dishwasher

Service Load Calculation:

Type of Occupancy = Dwelling Unit = Table 220.42

General Load: (for 8 units)

Lighting Load :

700 x 3 = 2100 VA

Small Appliance 3000 VA

Laundry 1500 VA

2100 + 3000 + 1500 = 6600 VA x 8 Residences = 52800 VA

First 3000 VA @100%    = 3000

Remainder VA @ 35%  = 49800 x .35 = 17430 VA

3000 + 17430 = 20430 VA

Heating Load: 100%

12,000 VA x 8 = 96000 VA

Dryer Load: Table 220.54

 Demand factor for 8 dryers 60%

5000 x 8 = 40000 x .6 = 24000 VA

Oven Load

Demand factor for ovens table 220.55 Column C

12000 x 8 = 96000 x .23 = 22080 VA

Other Loads Fasten in place

75% demand factor

Water Heater 5000 VA

Disposal 960 VA

Dishwasher 900 VA

5000 + 960 + 900 = 6860 x 8 = 54880 x .75 = 41160 VA


House Panel:

Elevator 4 KW

Lighting for Stairways, Halls, Corridors = 700 Sq Ft

Lighting load Table 220.12

700 x .5 = 350

Elevator Load = 4000 VA

Total with first 3000 @ 100% and remainder @ 35%

4000 + 350 = 4350 

3000 + 473 = 3473 VA

Total Volt Amps for Multifamily

20430 + 96000 + 24000 + 22080 + 41160 + 3473 = 207,143 VA

207,143 VA / 240 Volts = 863 Amps

Service Laterals: Table 310.15(B)(16)

Minimum gauge copper wire @ 75°

Parallel runs of 700 kcmil

or

Three runs of 350 kcmil

Note: Standard Amp Ratings... Article 240.6

1000 Amps is the common breaker size for this Service.

So your Service Laterals will need to be 1000 Amps or:

Three runs of 500 kcmil

Your Neutral will be:

Article 220.61 

General Lighting and Small appliance = 20430 VA

Other Loads = 41160 VA

House panel = 3473 VA

Oven Load = 22080 VA @ 70% = 15456 VA

Dryer Load = 24000 VA @ 70% = 16800 VA

20430+41160+3473+15456+16800= 97319 VA / 240 Volts = 405 Amps

If your running 500's though you will run 250 kcmil Neutrals. If you oversize the Line Conductors you will oversize the neutral by the same amount.

After all these calculation's what conduits will we be burying?