NEC Calculation Requirements, Part 8

NEC Calculation Requirements, Part 8Why is Section 210.11 (Branch Circuits Required) relevant to your circuit calculations? Think about what you size a conductor for – to carry the load. Before you can size the conductor, you need to determine what load it will carry.

You must do the calculations required in section 210.11 before you can do conductor sizing calculations for the branch circuits originating from a given branch circuit panel.

The number of branch circuits is a factor in how big (in amps) each circuit must be. Vice versa, you calculate the minimum number of branch circuits by dividing the total calculated load by the size (rating) of the circuits used [210.11(A)]. This may be an iterative process.

Key requirements of 210.11:

  • You must supply branch circuits for specific types of loads (in addition to circuits for general loads).
  • Where you calculate load on the basis of VA per square meter, it must be evenly proportioned among the multi-outlet branch circuits within the panelboards.
  • For dwelling units, you must provide a certain number of branch circuits depending on the characteristics of the unit. In addition, you must supply small-appliance, laundry, and bathroom branch circuits.

And Article 210 holds more requirements for the would-be conductor sizer to work through before doing those conductor calculations. Some individual types of circuits must be of a minimum ampacity [210.19]. If you glance at the requirements, you’ll notice most of the text is italicized. That is, it consists of exceptions.

« Part 7 | Part 9 » | Source: Mark Lamendola | Mindconnection

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