How to use the NEC feeder load calculator
Connected load and calculated load are two different numbers, because everything in a building never runs at full output at the same moment. The National Electrical Code handles that with demand factors, published by load category in Article 220 Part III. Enter your connected load, the applicable demand factor, power factor, and system voltage, and this tool returns calculated demand load, feeder design current, and the next standard overcurrent device size.
Feeders serving continuous loads, meaning loads expected to run three hours or more, must be sized at 125 percent of the continuous portion under 215.2 and 215.3. The selector applies that multiplier, and the resulting ampere figure is rounded up to the next standard rating listed in 240.6(A).
Do not guess at the demand factor. General lighting sits in 220.42, receptacle loads in 220.44, commercial kitchen equipment in 220.56, and motor loads follow Article 430 instead. Some national codes apply a separate diversity factor for non-coincident peaks; the NEC folds that allowance into its own tables, so only one demand factor per category is used here.
This is a preliminary sizing aid. Voltage drop over the run, ambient temperature and conduit fill corrections to conductor ampacity, harmonic loading, and future expansion are all outside its scope, so have a licensed electrical engineer or electrician confirm the final feeder and breaker selection.
Frequently asked questions
NEC Article 220 Part III lists them by load type and occupancy, including general lighting in 220.42, receptacle loads in 220.44, kitchen equipment in 220.56, and motors in Article 430. Read the applicable table rather than assuming a percentage.
Some national codes apply a separate diversity factor for non-coincident peaks. The NEC folds that allowance into its published demand factor tables instead, so a single demand factor per load category is applied.
No. Voltage drop over the run, ambient and conduit fill ampacity corrections, harmonics, and future expansion are not included. Have a licensed electrical engineer or electrician confirm the final feeder and overcurrent device.