Accurate load calculation is essential for sizing the electrical service of a residential dwelling. The Standard Method, outlined in NEC 2023, Article 220 Part III, provides a structured approach to determining the minimum service size based on connected loads and demand factors.

Here’s a step-by-step breakdown of how to perform the load calculation for a single-family home using the Standard Method.

Step 1: General Lighting and Receptacle Loads

Per NEC 220.12(A):

  • Use 3 VA per square foot of habitable space

  • Exclude open porches, garages, and unfinished basements

Example:
For a 1,800 ft² home:

1,800ft²×3VA=5,400VA

Step 2: Small Appliance and Laundry Circuit Loads

Per NEC 220.52:

  • Two small appliance circuits = 1,500 VA × 2 = 3,000 VA

  • One laundry circuit = 1,500 VA

Total = 4,500 VA

Step 3: Apply Demand Factors (Table 220.42)

Apply the following to the sum of general lighting and circuit loads:

Load Range Demand Factor
First 3,000 VA 100%
Next 117,000 VA 35%
Above 120,000 VA 25%

This adjustment accounts for typical residential diversity.

Step 4: Fastened-in-Place Appliances

Per NEC 220.53, include:

  • Dishwasher, garbage disposal, water heater, etc.

  • Use nameplate VA ratings

If 4 or more appliances are included (excluding HVAC), apply a 75% demand factor.

Step 5: Clothes Dryer

Per NEC 220.54:

  • Use 5,000 VA or nameplate rating (whichever is larger)

  • One dryer = 100% demand

Step 6: Cooking Equipment

Per NEC 220.55:

  • Use nameplate rating

  • Apply demand factor from Table 220.55 depending on quantity and size of ranges

Step 7: Heating or Air Conditioning

Per NEC 220.60, include only the larger of:

  • The total heating load (e.g., electric baseboard, furnace)

  • Or the total cooling load (e.g., air conditioning, heat pump)

Do not include both in the calculation.

Step 8: Total Load and Service Size

Add all adjusted loads together to determine total connected VA. Then, calculate:

Total Load (VA)÷240V=Amps Required

Round up to the next standard breaker size.

Conclusion

The Standard Method ensures safe, code-compliant service sizing tailored to real-world residential use. While more detailed than the Optional Method (NEC 220.82), it provides flexibility in load combinations and ensures proper demand factoring.

Always reference the latest NEC edition and coordinate with your local AHJ (Authority Having Jurisdiction).

Refer to the link below to begin the Optional Method load calculation for single dwelling unit:

Single Dwelling Unit