Electrical Load Calculator

Calculate electrical service size and panel loads using NEC Article 220 demand factors. Perfect for residential and commercial load calculations.

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What is Load Calculation?

Load calculation is the process of determining the total electrical demand for a building or facility to properly size the electrical service, feeders, and branch circuits. The NEC provides specific methods in Article 220 for calculating loads.

Proper load calculation ensures the electrical system can safely handle all connected loads while meeting code requirements. Undersized services can cause nuisance tripping, overheating, and safety hazards.

NEC General Lighting Loads (Table 220.12)

Occupancy TypeVA per Square Foot
Dwelling Units3 VA/sq ft
Hospitals2 VA/sq ft
Hotels/Motels2 VA/sq ft
Office Buildings3.5 VA/sq ft
Restaurants2 VA/sq ft
Schools3 VA/sq ft
Retail Stores3 VA/sq ft
Warehouses0.5 VA/sq ft

Dwelling Unit Demand Factors (Table 220.42)

For dwelling units, apply these demand factors to the general lighting, small appliance, and laundry loads:

First 3,000 VA100%
3,001 VA to 120,000 VA35%
Over 120,000 VA25%

Residential Load Calculation Steps

Step 1: General Lighting Load

Square footage × 3 VA/sq ft

Step 2: Small Appliance Circuits

Minimum 2 circuits × 1,500 VA = 3,000 VA

Step 3: Laundry Circuit

1 circuit × 1,500 VA = 1,500 VA

Step 4: Apply Demand Factors

First 3,000 VA at 100% + remainder at 35%

Step 5: Fixed Appliances

Add nameplate VA (75% if 4+ appliances)

Step 6: HVAC Load

Larger of heating or cooling (not both)

Step 7: Calculate Service Size

Total VA ÷ 240V = Service Amperage

Load Calculation Example

Problem:

Calculate the service load for a 2,000 sq ft dwelling with electric water heater (4,500W), electric dryer (5,000W), range (12,000W), and 5-ton AC (6,000W).

Solution:

General Lighting: 2,000 × 3 = 6,000 VA

Small Appliance: 2 × 1,500 = 3,000 VA

Laundry: 1,500 VA

Subtotal: 10,500 VA

Demand: 3,000 at 100% + 7,500 at 35% = 3,000 + 2,625 = 5,625 VA

Water Heater: 4,500 VA

Dryer: 5,000 VA

Range: 8,000 VA (from Table 220.55)

AC: 6,000 VA

Total: 5,625 + 4,500 + 5,000 + 8,000 + 6,000 = 29,125 VA

Service Size: 29,125 ÷ 240 = 121A → Use 150A Service

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