Example No. D2(b) Optional Calculation for One-Family Dwelling, Air Conditioning Larger than Heating [See 220.82(A) and 220.82(C)]

The dwelling has a floor area of 1500 square feet exclusive of an unfinished cellar not adaptable for future use, unfinished attic, and open porches. It has two 20-ampere small appliance circuits, one 20-ampere laundry circuit, two 4-kW wall-mounted ovens, one 5.1-kW counter-mounted cooking unit, a 4.5-kW water heater, a 1.2-kW dishwasher, a 5-kW combination clothes washer and dryer, six 7-ampere, 230-volt room air-conditioning units, and a 1.5-kW permanently installed bathroom space heater. Assume wall-mounted ovens, counter-mounted cooking unit, water heater, dishwasher, and combination clothes washer and dryer kW ratings equivalent to kVA.

Air Conditioning kVA Calculation

Load Included at 100%

Air conditioning: Included below [See Item 1 in 220.82(C)]

Space heater: Omit [See Item 5 in 220.82(C)]

General Load

 

1500 sq. ft. at 3 volt-amperes

4500 VA

Two 20-amp. small appliance circuits at 1500 volt-amperes each

3000 VA

Laundry circuit

1500 VA

2 ovens

8000 VA

1 cooking unit

5100 VA

Water heater

4500 VA

Dishwasher

1200 VA

Washer/dryer

5000 VA

Total general load

32,800 VA

1st 10 kVA at 100%

10,000 VA

Remainder at 40% (22.8 kVA x .4 x 1000)

9,120 VA

Subtotal general load

19,120 VA

Air conditioning

10,080 VA

Total

29,200 VA

Calculated Load for Service

Feeder Neutral Load (per 220.61)

Assume that the two 4-kVA wall-mounted ovens are supplied by one branch circuit, the 5.1-kVA counter-mounted cooking unit by a separate circuit.

1500 sq. ft. at 3 volt-amperes

4500 VA

Three 20-amp circuits at 1500 volt-amperes

4500 VA

Subtotal

9000 VA

3000 volt-amperes at 100%

3000 VA

9000 VA - 3000 VA = 6000 volt-amperes at 35%

2100 VA

Subtotal

5100 VA

Two 4-kVA ovens plus one 5.1-kVA cooking unit = 13.1 kVA.

Table 220.55 permits 55% demand factor or

Subtotal from above

5100 VA

Ovens and cooking unit: 7200 VA x 70% for neutral load

5040 VA

Clothes washer/dryer - 5 kVA x 70% for neutral load

3500 VA

Dishwasher

1200 VA

Total

14,840 VA

Calculated Load for Neutral






Pocket Guide to the National Electrical Code 2005
Pocket Guide to the National Electrical Code(R), 2005 Edition (8th Edition)
ISBN: 0131480014
EAN: 2147483647
Year: 2004
Pages: 120
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