Key Differences from Residential
Commercial load calculations differ from residential in several important ways: (1) lighting load per square foot varies by building type (NEC Table 220.12), (2) receptacle loads are calculated per outlet rather than per circuit, (3) no standard demand factor for appliances — each piece of equipment uses nameplate rating, (4) HVAC loads are typically much larger and may include multiple systems.
Commercial buildings also require a thorough analysis of connected equipment — data centers, commercial kitchens, manufacturing equipment — each with unique demand characteristics not covered by standard NEC tables.
General Lighting Load
NEC Table 220.12 provides unit lighting loads by occupancy: Offices = 3.5 VA/ft², Retail Stores = 1.5 VA/ft², Restaurants = 2 VA/ft², Warehouses = 0.5 VA/ft², Schools = 3 VA/ft², Hotels = 2 VA/ft², Hospitals = 2 VA/ft².
The general lighting load from Table 220.12 includes all general-use receptacles per NEC 220.14(J). Dedicated receptacle outlets and specific equipment are calculated separately.
Demand factors from Table 220.42 apply to the total general lighting load. For most commercial occupancies: first 12,500 VA at 100%, remainder at 50%. For warehouses/storage: first 12,500 VA at 100%, all remaining at 50%.
Receptacle and Equipment Loads
General-purpose receptacles not covered by Table 220.12: 180 VA per single or duplex receptacle outlet per NEC 220.14(I). For multioutlet assemblies: 180 VA per 5-foot section (or per 1-foot section in commercial/industrial areas where simultaneous use is likely).
NEC 220.44 demand factor for receptacles: when the receptacle load exceeds 10 kVA, apply: first 10 kVA at 100%, remainder at 50%. This recognizes that not all receptacles in a commercial building operate simultaneously.
Sign/outline lighting: NEC 220.14(F) requires a minimum 1,200 VA for each required sign circuit per NEC 600.5.
Show window lighting: 200 VA per linear foot of show window per NEC 220.14(G).
HVAC and Special Loads
HVAC equipment: Use nameplate MCA (Minimum Circuit Ampacity) × voltage for VA calculation. For rooftop units with multiple compressors, include all compressor and fan loads.
Kitchen equipment (NEC Table 220.56): For commercial kitchens with 3+ pieces of equipment, apply demand factors: 3 units = 90%, 4 = 80%, 5 = 70%, 6+ = 65%. This dramatically reduces the calculated kitchen load.
Elevator motors: Use nameplate rating at 100%. For multiple elevators, apply demand factor per building use patterns (typically largest at 100%, each additional at 50-75%).
Noncoincident loads (NEC 220.60): Use only the larger of heating or cooling, same as residential. This applies to each independently controlled HVAC zone.
Service Sizing Example
Example: 20,000 sq ft office building. General lighting: 20,000 × 3.5 = 70,000 VA. Demand: first 12,500 at 100% + 57,500 at 50% = 41,250 VA. Receptacles: 200 outlets × 180 VA = 36,000 VA. Demand: first 10,000 at 100% + 26,000 at 50% = 23,000 VA.
HVAC: 3 × 25-ton RTU at 65A each × 480V × √3 = 162,136 VA. Kitchen: none. Elevator: 1 × 25 HP = 25,864 VA + 25% motor = 6,466 VA.
Total: 41,250 + 23,000 + 162,136 + 25,864 + 6,466 = 258,716 VA. Service: 258,716 / (480 × 1.732) = 311A → 400A service with 480V 3-phase.