Apply NEC Article 220 demand factors for dwellings, commercial, hotels, and warehouses. See connected vs. demand load with a full tier-by-tier breakdown.
Demand factors allow engineers to design electrical systems based on realistic load diversity rather than the worst-case assumption that every load runs simultaneously at 100%. NEC Article 220 provides demand factors for general lighting, small appliance circuits, laundry circuits, ranges, dryers, and fixed appliances based on statistical occupancy patterns.
Applying demand factors is not optional — it is a deliberate NEC design method that produces a code-compliant, cost-effective service size. However, demand factors only apply to the specific loads and occupancy types listed in NEC Article 220.
NEC 220.82(B)(3) allows the Optional Method to use the largest HVAC or heating load at 100% (not both). The Standard Method per 220.42 applies demand factors only to general lighting. HVAC, ranges, dryers, and water heaters have their own demand factor tables (NEC 220.54, 220.55, 220.56).
NEC Table 220.84 provides demand factors for multi-family dwellings based on the number of units. For 3 units: 45%, for 10 units: 43%, for 20 units: 38%, for 30 units: 35%, for 40 units: 32%, for 50+ units: 26–28%. This allows very significant feeder size reductions in large apartment buildings.
Ranges and dryers use separate NEC demand factor tables (NEC 220.55 and 220.54), which are different from the general lighting demand factors in Table 220.42. For example, a single 12 kW household range has a demand of 8 kW per NEC Table 220.55, Column C — a built-in 33% reduction before any other calculations.
NEC Table 220.42 provides demand factors for general lighting in commercial occupancies. Stores get first 12,500 VA at 100% and remainder at 50%. Banks and office buildings are treated as "other" commercial occupancies — all lighting at 100%, with no demand factor reduction unless specifically listed.