Rules for Sizing branch-circuit conductors and overcurrent protection

by Gerald Newton
October 29, 1999

There are many rules in the 1999 National Electrical Code for calculating loads, determining the correct size conductors, and determining the correct overcurrent protection.  Simply put, conductors shall be sized to carry the load without overheating, and the conductors and equipment shall be protected  from overcurrent to prevent overheating.  Additionally, although not addressed here, this overcurrent protection usually provides ground-fault and short circuit protection.

The general rules for branch circuits as found in Section 210 of the NEC can be divided into these parts:

Sizing the Conductors

Selecting the overcurrent protection Selecting conductors and overcurrent protection based on temperature limitations. Some important Definitions Exceptions and Tricky Rules

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