What is a demand factor in electrical calculations?
A demand factor is a multiplier applied to electrical loads to account for the fact that not all loads operate simultaneously at full capacity. It helps determine the actual electrical demand rather than the connected load. See also our Raceway Fill Calculator.
How is the general load calculated for residential properties?
General load is calculated at 3VA per square foot of living area, plus 1500VA for each small appliance circuit (minimum 2), plus 1500VA for each laundry circuit, according to NEC requirements.
What demand factors apply to general lighting and receptacle loads?
The first 3000VA is at 100%, the next 117,000VA (3001-120,000VA) is at 35%, and any amount over 120,000VA is at 25%, per NEC Table 220.42.
How are major appliances factored into demand calculations?
Major appliances like ranges, dryers, and ovens have specific demand factors. Electric ranges use NEC Table 220.55, while other appliances are typically calculated at 100% of their nameplate rating.
What service size should I choose based on the demand calculation?
The service ampacity should be at least 100A for residential properties. Common sizes are 100A, 125A, 150A, and 200A. Choose the next standard size above your calculated demand load divided by 240V.
Are HVAC loads included at 100% in demand calculations?
HVAC loads are typically included at 100% of their nameplate rating, but only the larger of heating or air conditioning is counted since they don't operate simultaneously.
Why don't we add up all connected loads for service sizing?
Adding all connected loads would result in oversized electrical services. Demand factors account for diversity in load usage - not all electrical devices operate at maximum capacity simultaneously. You might also find our Service Entrance Calculator useful.