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Branch Circuit Load Calculations

Tuesday, June 22nd, 2010

The NEC requires that branch circuits be sized to serve 125% of the continuous load and 100% of the noncontinuous load (NEC 210.20(A)). Design Master Electrical includes an option to calculate the branch circuit load at 125% of both the continuous and noncontinuous. This is a more conservative approach than what the NEC requires. You can change this setting using the Size breakers to 100% of noncontinuous load setting in the Circuits, Load Types, and Wire Sizes section of the Options menu.

Ribbon: DME: Customization->Project Customization-> dm_dm-optionP Options

Pulldown Menu: DM Electrical->Customization->Options->Edit Project List

The load types are broken down between continuous and noncontinuous as follows:

Continuous

  • Lighting
  • Motors (NEC 430.24)
    • Largest Motor
    • Other Motors
    • Cooling, Largest Motor
    • Cooling, Other Motors
    • Heating and Cooling Motor
    • Appliance Motor
  • Continuous
  • Heating (NEC 424.4(B))
  • Appliance, Continuous

Noncontinuous

  • Receptacles (NEC Handbook Exhibit 220.4)
  • Noncontinuous
  • Kitchen
  • Diverse
  • Small Appliance
  • Laundry
  • Appliance, Noncontinuous
  • Electric Dryer
  • Electric Cooking
  • Marina / Mobile Home / RV

When you create a custom load type, you specify whether it should be treated as a continuous or noncontinuous load for branch circuit sizing. Do this using the Custom Load Type: Load Type setting in the Circuits, Load Types, and Wire Sizes section of the Options menu.

All motors are considered continuous at the branch circuit level.

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