Commercial Electrical Load Calculation Worksheet
1. General Lighting & Area
Office Buildings (3.5 VA/sqft)
Retail Stores (3.0 VA/sqft)
Restaurants (2.0 VA/sqft)
Warehouses (0.25 VA/sqft)
Hospitals (1.0 VA/sqft)
Schools (2.0 VA/sqft)
Hotels/Motels (0.5 VA/sqft)
2. Specific Load Requirements
3. Motor & System Configuration
208V
240V
480V
120V
Single Phase (1φ)
Three Phase (3φ)
General Lighting Load:
0 VA
Sign Circuit Load:
0 VA
Demand Receptacle Load:
0 VA
Motor & Equipment Load:
0 VA
Total Calculated Load:
0 VA
Required Service Amps:
0 A
*Note: Calculation includes the NEC 125% factor for the largest motor and continuous loads.
Understanding Commercial Electrical Load Calculations
A commercial load calculation worksheet is a vital tool for electrical engineers, contractors, and building owners to determine the sizing of electrical service equipment. Unlike residential calculations, commercial loads are governed by specific NEC (National Electrical Code) sections, primarily Article 220, which accounts for higher usage patterns and specialized equipment.
Key Components of the Calculation
To accurately size a commercial panel, you must categorize your loads into several buckets:
- General Lighting: Calculated based on the square footage of the building. Different types of occupancies (e.g., an office vs. a warehouse) have different Volt-Amp (VA) requirements per square foot.
- Receptacle Loads: For commercial spaces, the first 10,000 VA of receptacle load is calculated at 100%, while the remainder is usually calculated at 50% demand factor.
- Sign Circuits: The NEC requires at least one 1,200 VA branch circuit for each commercial occupancy's sign or outline lighting.
- Motor Loads: Motors represent a dynamic load. Code requires taking 125% of the largest motor's VA rating and 100% of all other motors to account for startup surges.
- HVAC: You must calculate both the heating and cooling loads and use the larger of the two, as they typically do not run simultaneously.
Single-Phase vs. Three-Phase Logic
Commercial buildings often utilize 3-phase power (208V or 480V). When calculating the final amperage for a 3-phase system, the formula includes the square root of 3 (approximately 1.732). This allows for more efficient power delivery compared to standard single-phase residential services.
Example Calculation
Imagine a 2,000 sq. ft. Retail Store with a total receptacle load of 15,000 VA and an HVAC unit of 10,000 VA.
- Lighting: 2,000 sq. ft. x 3.0 VA = 6,000 VA.
- Receptacles: 10,000 VA (at 100%) + 5,000 VA (at 50%) = 12,500 VA.
- Sign: 1,200 VA.
- HVAC: 10,000 VA.
- Total: 29,700 VA.
- Amperage (3-Phase 208V): 29,700 / (208 x 1.732) = 82.4 Amps.
In this scenario, a 100-amp or 125-amp service would likely be specified to allow for future expansion.