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Optional Feeder and Service Calculations, Part 2

Previously, we said you can use the time-saving optional method if you have certain information. You could even put together a project review checklist to allow you to quickly assess whether you must use the standard method instead. However you lay out your checklist, it needs to show these requirements for using the optional method for these applications:

  • School [220.86]: It's equipped with AC and/or electric space heating.
  • Existing loads [220.87]: You have the maximum demand data for the past year, the maximum demand at 125% plus the new load won't exceed the service or feeder ampacity, and you protect the feeder per 240.4 or service per 230.90.
  • Restaurant [220.88]: The feeder serves the total load.
  • Dwelling unit [220.82]: Regardless of the type of dwelling unit, to qualify for the optional method it must have a total connected load served by single 120/240V or 208Y/120V 3-wire service or feeder with at least 100A ampacity.

If the dwelling unit qualifies, then assess whether it is:

  • Existing dwelling unit [220.83]: Use the optional method only if the feeder or service can carry additional loads.
  • Multi-family dwelling unit [220.84]: Use the optional method only if each unit has electric cooking equipment and heat or AC, plus no more than one feeder.
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