What is a demand factor in electrical load calculations?
A demand factor lets you size a service or feeder for the load that actually runs at once, not every connected watt. Article 220 gives the factors. For dwelling general lighting, you take the first 3,000 VA at 100 percent and the remainder at 35 percent. The factors keep you from oversizing for loads that never all run together.
Last reviewed June 2026 · Answered by JourneymanIQ staff
What it does
A demand factor reduces the calculated load to reflect what realistically runs at the same time, so you do not size a service for every connected watt.
Where the factors live
Article 220 holds them: 220.42 for general lighting, 220.55 for ranges, 220.54 for dryers. Apply each at the right step of the calculation.
The dwelling lighting example
Take the first 3,000 VA of general lighting at 100 percent, then the remainder at 35 percent. That single rule shows up on a lot of dwelling load questions.
Demand factors size for what runs at once. Article 220 gives them. First 3,000 VA at 100, the rest at 35.
Practice questions and explanations on JourneymanIQ are original. We paraphrase the NEC and cite article numbers, and we do not reproduce NEC text or real exam questions.
Find your weak topics before test day
The diagnostic is free, 15 questions, no signup. It shows you which NEC sections to focus on, in priority order.