What is a demand factor?

A demand factor is the ratio of the load that is actually expected to run at peak to the total connected load. The NEC publishes these factors in Article 220 because appliances rarely all run at full power simultaneously, which lets you size a smaller, cheaper, and still-safe feeder or service.

How does the 220.42 general lighting demand work?

The first 3000 VA of general lighting and receptacle load is counted at 100%, the portion from 3001 to 120000 VA at 35%, and anything above 120000 VA at 25%. Small-appliance and laundry circuits are added to the general load before this factor is applied.

How are electric ranges handled by 220.55?

Household ranges not over 12 kW use Table 220.55 Column C. One range demands 8 kW, two demand 11 kW, three demand 14 kW, and so on, rather than summing each range nameplate. This reflects that multiple ranges almost never peak at the same instant.

What demand factor applies to electric dryers?

NEC 220.54 sets a minimum dryer load of 5000 VA each, counted at 100% for up to four dryers. From five dryers up, a declining demand factor applies, starting at 85% for five and dropping further as the count rises in multi-unit buildings.

Is this the standard or optional calculation method?

This tool implements the standard Article 220 method using the individual demand factors for lighting, small appliances, dryers, and ranges. The optional method in 220.82 uses a single combined factor and is often used for dwellings, so check which your jurisdiction requires.

NEC Demand Factor Calculator

NEC Article 220 lets you reduce a building’s raw connected load to a realistic demand load because not every appliance runs at full power at once. This calculator walks through the 220.42 general lighting factor, the 220.52 small-appliance and laundry additions, the 220.54 dryer factor, and the 220.55 Column C range table to produce a feeder or service demand load for permit submissions.

How it works

Each load category gets its own demand treatment, then they are summed:

general connected = general lighting VA + (small-appliance + laundry circuits) × 1500
general demand    = first 3000 VA × 100% + 3001–120000 × 35% + above 120000 × 25%
dryer demand      = max(nameplate, 5000) × count × table 220.54 factor
range demand      = Table 220.55 Column C kW for the range count
total demand      = general demand + dryer demand + range demand

The general lighting factor does most of the work: above the first 3000 VA only 35% of the load counts, which can roughly halve a large dwelling’s calculated lighting load.

Example and tips

A 1500 sq ft dwelling has 1500 × 3 = 4500 VA general lighting. Adding two small-appliance circuits and one laundry circuit brings the connected general load to 4500 + 3 × 1500 = 9000 VA. The 220.42 factor gives 3000 + (9000 − 3000) × 0.35 = 5100 VA. One 5000 VA dryer at 100% and one range at 8 kW push the total to about 5100 + 5000 + 8000 = 18,100 VA. Tips: add small-appliance and laundry circuits before the 220.42 factor, not after; use Column C only for ranges not exceeding 12 kW; and add heating, cooling, EV, and motor loads separately, since they are not part of these particular factors.