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Electrical Load Calculator

Calculate the total electrical load for residential and small commercial buildings following NEC Article 220 standard method for load calculations.

How to Calculate Electrical Load

What Is Electrical Load Calculation?

An electrical load calculation determines the total power demand of a building to properly size the electrical service (panel) and feeders. It accounts for lighting, receptacles, appliances, HVAC, and other fixed equipment. The NEC provides a standard method in Article 220 that uses demand factors — these allow you to reduce certain loads because not everything runs at full power simultaneously.

NEC 220 Standard Method

General Lighting Load = Square Footage × 3 VA (NEC 220.12)

Small Appliance Circuits = 2 (min) × 1500 VA (NEC 220.52(A))

Laundry Circuit = 1500 VA (NEC 220.52(B))

Demand Factor: First 3,000 VA at 100%, remainder at 35%

Add fixed appliances (dryer, range, HVAC, water heater) per their respective NEC demand tables.

The key insight is that NEC allows demand factors because you never use every appliance at full power simultaneously. For general lighting, only the portion above 3,000 VA is reduced to 35%. For ranges, NEC Table 220.55 provides specific demand values — a 12 kW range is calculated at only 8 kW.

Worked Example: 2,000 sq ft Home

  1. General lighting: 2,000 × 3 = 6,000 VA
  2. Small appliance circuits: 2 × 1,500 = 3,000 VA
  3. Laundry circuit: 1,500 VA
  4. Subtotal: 10,500 VA
  5. Apply demand factor: 3,000 + (10,500 − 3,000) × 0.35 = 5,625 VA
  6. Range (12 kW): 8,000 VA (per NEC Table 220.55)
  7. Dryer (5 kW): 5,000 VA (NEC 220.54)
  8. HVAC: 10,000 VA
  9. Water heater: 4,500 VA
  10. Total demand: 5,625 + 8,000 + 5,000 + 10,000 + 4,500 = 33,125 VA
  11. Total amps: 33,125 / 240 = 138A → Recommend 150A or 200A service

Practical Tips

  • For HVAC, use the larger of heating or cooling load — they don't run simultaneously.
  • Modern homes with electric vehicles, hot tubs, or large shops often need 200A or even 400A service.
  • Standard residential service sizes are 100A, 150A, 200A, and 400A. Always round up.
  • For commercial buildings, the optional method (NEC 220.84) may yield different results than the standard method.

Code References

NEC 220.12, NEC 220.14, NEC 220.42, NEC 220.50, NEC 220.52, NEC 220.54

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Frequently Asked Questions

What is the NEC standard method for residential load calculations?
NEC Article 220 standard method: (1) General lighting = sq ft × 3 VA, (2) Small appliance circuits = min 2 × 1500 VA, (3) Laundry circuit = 1500 VA, (4) Apply demand factor to the sum of items 1–3 (first 3000 VA at 100%, remainder at 35%), (5) Add fixed appliances (dryer, range, water heater, HVAC), (6) Apply demand factors per NEC tables for specific appliances.
How do I determine what size electrical service I need?
Calculate the total demand load in VA, divide by 240V to get amps, then round up to the nearest standard service size. Standard residential sizes are 100A, 150A, 200A, and 400A. For most modern homes with electric appliances, 200A service is recommended. For homes with gas heating and cooking, 100-150A may suffice.
Do I need to include all appliances at full load?
Not always. NEC allows demand factors for certain loads. For example, the range demand is calculated per NEC Table 220.55 (8 kW for a 12 kW range). HVAC and heating loads use the larger of heating or cooling, not both simultaneously. General lighting and receptacles get a 35% demand factor for the portion over 3000 VA.