Article 220
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 water heater, 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
Go to annex D in your code book for reference. Example D1(a)
Using your calculator multiply 2500 x 3 = 7500
Small appliance load = 3000
Laundry load = 1500
Using your calculator add 7500, 3000, 1500 = 12000 now subtract 3000 = 9000 now multiply by .35 = 3150 now add 3000 = 6150
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
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
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..
Multi-Family Dwelling Unit Calculation Sheet
NEC Article 220.82
Turn Phone Sideways
This is an example of how to calculate an apartment building with some commercial space and some common areas.
This building has:
Common/ Amenity……… 13,848 SF
Commercial………………9,703 SF
Apartments……………….59,544 SF
Apartments…..46 units each with 782.5 SF
NEC REFERENCE
220.82(b)(1)
GENERAL LIGHTING AND RECEPTACLES
3 VA/SF NEC STANDARD
107,979 VA CALCULATED GENERAL LIGHTING VA
220.82(B)(2)
SMALL APPLIANCE BRANCH CIRCUIT LOAD
1500 VA NEC STANDARD VA/CIRCUIT
2 EA TWO (2) CIRCUITS / UNIT
3000 VA SMALL APPLIANCE VA / UNIT
138,000 VA TOTAL SMALL APPLIANCE/ LAUNDRY VA
220.82(B)(3)(a)
APPLIANCES, PERMANENTLY INSTALLED
1068 VA DISHWASHER, PRODUCT DATA
49,128 VA TOTAL APPLIANCE VA
220.82(B)(3)(b)
RANGES
10,200 VA PRODUCT DATA (MAX)
469,200 VA TOTAL RANGES VA
220.82(B)(3)(d)
LAUNDRY COMBINED WASHER/DRYER
5100 VA PRODUCT DATA (STACKED UNITS)
234,600 VA TOTAL LAUNDRY VA
220.83(B)(3)(d)
WATER HEATERS
4,500 VA 208V/1PH/30AMP CIRCUIT
207,000 VA TOTAL WATER HEATER
220.82(B)(4)
MOTORS, NON-APPLIANCE
0 VA NONE ASSUMED
0 VA TOTAL MOTOR VA
220.82 ( C)
HEATING AND AIR-CONDITIONING
0 VA HEATING, UNIT HEATER
668 A HEAT PUMP SYSTEM AMPS (TOTAL)
208 V HEAT PUMP SYSTEM VOLTS / 1-PHASE
138,986 VA HEAT PUMP SYSTEM, TOTAL (apt.)
138,986 VA HEAT PUMP SYSTEM LOAD
TOTAL Apartments
1,344,893 VA TOTAL SUMMED VA, APARTMENTS (FROM ABOVE)
26% % NEC TABLE 220.84 DEMAND FACTOR FOR MULTIFAMILY DWELLING UNITS (46-50)
349,672 VA ADJUSTED VA, APARTMENTS
see below (total Amps for apartments only)
TOTAL Common Area
1 VA/SF LIGHTING & BRANCH CIRCUITS, COMMON/AMENITY SPACES
13,848 VA LIGHTING & BRANCH CIRCUITS TOTAL, COMMON/AMENITY SPACES
31.5 A HVAC AMPS, COMMON/AMENITY SPACES (FITNESS ROOM ONLY)
6,552 VA HVAC TOTAL, COMMON/AMENITY SPACES
78.2 A ELEVATOR #1- 25HP
142 A ELEVATOR #2- 50HP
79,328 VA ELEVATOR MOTORS TOTAL
Total Commercial Space
50 KW COMMERCIAL SPACE (BREWERY): EXISTING DEMAND (40 KW)+ 25%
50,000 VA COMMERCIAL SPACE (BREWERY) TOTAL
160 A COMMERCIAL SPACE (RESTAURANT): ASSUME 80% DEMAND OF 200A/3PHASE
57,641 VA COMMERCIAL SPACE (RESTAURANT) TOTAL
Total Building
557,041 VA TOTAL BUILDING VA, SUMMED
1,546.20 A CALCULATED AMPS, BASED ON 208V/3PH SERVICE
970.6 A 208V/3PHASE AMPS FOR (46) RESIDENTIAL UNITS
This is an example service feeder calculation for an 8 unit Brownstone in Boston.
The building has:
Common Area………………..700 SF
Apartments…...………………5600 SF
Apartments…………8 units. Each with 700 SF
General Lighting and Receptacle Loads
3 VA/SF
3 VA x 5600 SF = 16,800 VA
16,800 VA Calculated General Lighting VA
Small Appliance Branch Circuit Load / Laundry
1500 VA
2 EA
3000 VA/Unit x 8 units = 24,000 VA
1500 VA/Unit x 8 units = 12,000 VA
36000 VA Total Small Appliance VA and Laundry
Total Connected Load
Water Heater (5000 VA)
Disposal (940 VA)
Dishwasher (1,250 VA)
Dryer (4000 VA)
Oven (9000 VA)
15,690 VA/unit x 8 unit
125,520 VA Total Connected load
Heating and A/C load
Heater 12,000 VA/ unit x 8 unit
96,000 VA Total Heating Load
Total Apartment Load
16,800 VA general
36,000 VA small appliance / laundry
125,520 VA total connected
96,000 VA total heating
274,320 VA Total of all apartments
43% adjustment factor from Table 220.84
117,985 VA adjusted total
Common Area
Lighting and Branch Circuits
700 VA 1 VA/SF
12000 VA Heaters
4000 VA Elevator
16,700 VA Total
Total Building Sum
117,985 VA (Apartments)
16,700 VA ( Common Area)
134,685 VA / 240 Volt = 562 Amp
Table 240.6(A) Standard size inverse time circuit breaker
600 Amp
Table 310.16
copper 350 Kcmil @ 75° = 310 Amps
Parallel runs of 350.
