Electrical service size is set by a load calculation, not by house size alone. The optional method in NEC 220.82 is the most common way to size an existing or new single-family dwelling.
What 100 A and 200 A mean
A 240 V single-phase service delivers 24 kVA at 100 A and 48 kVA at 200 A. Standard service ratings include 100, 125, 150 and 200 A (NEC 240.6(A)).
Worked example: 2,000 sq ft home
- General lighting and receptacles: 2,000 × 3 VA = 6,000 VA
- Two small-appliance circuits: 2 × 1,500 = 3,000 VA
- Laundry circuit: 1,500 VA
- Range 12,000 VA, dryer 5,000 VA, water heater 4,500 VA, dishwasher 1,200 VA = 22,700 VA
Total before demand: 33,200 VA. Under 220.82(B), the first 10 kVA counts at 100% and the remainder at 40%: 10,000 + (23,200 × 0.40) = 19,280 VA. Add the larger of the heating or cooling load (220.82(C)), here a 5,000 VA air conditioner: 24,280 VA. At 240 V that is 24,280 ÷ 240 = about 101 A.
This house is slightly over 100 A, so a 125, 150 or 200 A service is appropriate.
Adding an EV charger
A 48 A EV charger draws 11,520 VA at 240 V. Adding it brings the calculated load to about 35,800 VA, or 149 A, so 150 A is the minimum and 200 A gives room to grow.
When 100 A may be enough
Small homes with gas heat, gas cooking and gas water heating, and no planned EV or heat pump, can often calculate under 100 A. Always run the calculation for your specific house, and have an electrician verify the existing panel, meter and utility requirements before ordering equipment.
Try the calculators
For informational and educational purposes only. Always consult a licensed electrician and local code authority. See our Electrical & Legal Disclaimer. Found an error? Tell us.