Lighting Load Demand Factors

Load CalculationsNEC 2023CEC Equivalent: CEC Table 14

Demand factors acknowledge that real-world usage patterns mean the entire lighting load will rarely be operating simultaneously. For dwelling units, the first 3,000 VA of general lighting load is calculated at 100 percent, the next 117,000 VA at 35 percent, and anything above 120,000 VA at 25 percent. This means a large house gets proportionally less demand as the square footage increases, which makes sense — nobody turns on every single light in a mansion at once. Hospitals, hotels, and motels have their own set of demand factors. Warehouses get an aggressive 50 percent demand factor on the first 12,500 VA and 50 percent on the remainder. There is a key limitation: these factors do not apply to areas where the entire lighting load is likely to be on simultaneously, such as operating rooms, ballrooms, or dining rooms in hotels and hospitals.

When You Need This

Performing the feeder or service load calculation for any dwelling unit
Sizing a service for a hotel, hospital, or warehouse where lighting is a significant portion of the load
Justifying a smaller service size by properly applying demand factors
Answering exam questions about residential or commercial load calculations

Key Points

1Dwelling units: first 3,000 VA at 100 percent, next 117,000 VA at 35 percent, remainder at 25 percent

2Hospitals: first 50,000 VA at 40 percent, remainder at 20 percent (with exceptions for spaces where all lights are on)

3Hotels and motels: first 20,000 VA at 50 percent, next 80,000 VA at 40 percent, remainder at 30 percent

4Warehouses: first 12,500 VA at 100 percent, remainder at 50 percent

5These factors only apply to feeders and services, not to individual branch circuits

6Spaces where all lighting is likely to operate simultaneously (operating rooms, ballrooms) are excluded from these reductions

Common Mistakes

Applying demand factors at the branch-circuit level — these factors only apply to feeders and services

Using dwelling unit demand factors for a commercial occupancy that has its own demand factor schedule

Applying demand factors to areas where all lighting is expected to be on at the same time

Forgetting to calculate the total lighting load from 220.12 BEFORE applying the demand factors

Mixing up the 220.42 lighting demand factors with the 220.54 dryer demand factors or 220.55 cooking demand factors

Exam Tip

For dwelling units, memorize the breakpoints: first 3,000 VA at 100 percent, remainder at 35 percent for typical residential calculations. On the exam, calculate the total general lighting load plus the small-appliance and laundry loads, then apply the demand factors to that combined number.

Frequently Asked Questions

Yes, for dwelling units, the small-appliance branch circuit loads (1,500 VA each) and laundry circuit load (1,500 VA) are added to the general lighting load before applying the demand factors from Table 220.42.

Table 220.42 does not list a specific demand factor for office buildings. However, NEC 220.42(B) permits using the listed demand factors for the occupancy type that most closely matches your building. Check with your local AHJ for guidance on unlisted occupancy types.

Inline Tools

Dwelling Load Calculator

Calculate residential service load per NEC 220

Related Code Sections

220.12General Lighting Loads 220.82Optional Method for Dwelling Unit Load Calculations

This is an educational summary, not the official code text. The NEC® is a registered trademark and copyright © National Fire Protection Association (NFPA). The CEC is copyright © CSA Group. For official code text, visit nfpa.org or csagroup.org. SparkShift is not affiliated with NFPA or CSA Group.