Electrical Load Calculator
Calculate electrical service size and panel loads using NEC Article 220 demand factors. Perfect for residential and commercial load calculations.
Use Calculator in AppWhat 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 Type | VA per Square Foot |
|---|---|
| Dwelling Units | 3 VA/sq ft |
| Hospitals | 2 VA/sq ft |
| Hotels/Motels | 2 VA/sq ft |
| Office Buildings | 3.5 VA/sq ft |
| Restaurants | 2 VA/sq ft |
| Schools | 3 VA/sq ft |
| Retail Stores | 3 VA/sq ft |
| Warehouses | 0.5 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:
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
Quick Load Calcs with Ampora
Enter your loads and get instant service sizing with automatic demand factor application. All NEC tables built-in.
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