Demand Factor
Also known as: Diversity factorNEC demand factorload diversity
Demand factor is the NEC's recognition that not all electrical loads run simultaneously at full capacity. If you have a 50A range, a 30A dryer, a 30A water heater, a 5-ton AC, and 12 lighting circuits, the sum of their nameplate ratings is much higher than the maximum load your panel actually sees at any one moment — because nobody runs all of them at peak simultaneously.
The demand factors are category-specific. On the general lighting and receptacle pool, the first 3,000 VA counts in full and everything above it at 35% — so a 1,800 sqft house with a 9,900 VA pool has a calculated demand of 3,000 + (6,900 × 0.35) = 5,415 VA, not 9,900. Appliances fastened in place drop to 75% once there are four or more of them. A single range up to 12 kW counts as 8,000 VA regardless of its nameplate.
Some loads get no demand factor at all. Heating and cooling are compared and only the larger is carried, since they don't run together. EV charging is added at full value, outside every factor above — which is why a charger moves the number more than homeowners expect.
The sum of every nameplate in your house is a much bigger number than the load your service actually sees, and demand factors are the code's way of accounting for that. It cuts both ways: the factors are why a panel often has more room than a gut check suggests, and the loads that sit outside them — an EV charger above all — are why a panel sometimes has less. The calculation is what settles it, not the instinct.
The 80% rule (continuous load limit on the main breaker) and the code's demand factors decide this together, and the honest answer is that it depends on the house. We run the math; if your panel handles the new load, we install the circuit. If it doesn't, we upgrade. We don't upgrade preemptively to pad the ticket.
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