Article 220 — Branch-Circuit, Feeder & Service Load Calculations

Article 220 is the calculation engine of Chapter 2. It defines how to add up lighting, receptacle, appliance, motor, and HVAC loads, and where you are allowed to apply demand factors because not everything runs at full load at once. It provides both a standard method and an optional method for dwellings.

The output feeds every sizing decision: service size, feeder ampacity, and the number of branch circuits. Getting the demand factors right is what separates a right-sized 200 A service from an oversized, overpriced one — or an undersized one that trips.

When it applies

Article 220 is the calculation backbone for the whole service. Any time you size a panel, a feeder, or the branch circuits behind it, this is where the numbers come from. You total the lighting by area, add fixed and appliance loads, then apply demand factors so the result reflects realistic simultaneous use instead of everything at full tilt.

Common mistakes

• Adding up connected load and stopping there, skipping the demand factors that keep the service sensibly sized.
• Leaving out the largest motor's required additional percentage.
• Mixing up the standard and optional calculation methods midway through.

In the field

On every service upgrade I do a clean Article 220 calc and keep it with the permit. It is the document that proves the service is right, and inspectors respect a load sheet that shows the work.