Load Calculations and Demand Factors
Standard method
Article 220 general lighting is 3 VA per square foot for dwellings. Add 1500 VA for each 20 A small-appliance circuit (minimum two) and 1500 VA for the laundry circuit. Apply Table 220.42 demand factors: first 3000 VA at 100%, from 3001 to 120,000 VA at 35%, and the remainder at 25%. Fixed appliances use 220.53: 75% of the total when four or more are connected. Ranges and dryers use Tables 220.55 and 220.54, not simple addition.
Optional method
220.82 lets a dwelling use 100% of the first 10 kVA plus 40% of the remainder for general loads, then add heating or air conditioning (the larger), plus the largest motor. It is not always the smaller answer - compute both.
Traps
Applying demand factors to loads that do not qualify, using the larger of heat and A/C instead of adding them, forgetting the 125% factor for continuous loads, and mishandling the neutral calculation under 220.61.
Worked example
A 2,000 ft² dwelling: lighting 6,000 VA + 3,000 VA small appliance + 1,500 VA laundry = 10,500 VA. Apply Table 220.42: 3,000 at 100% = 3,000; remaining 7,500 at 35% = 2,625; total 5,625 VA. Add the range, dryer, water heater, and the larger of heat or A/C to finish the service calculation.