Section 210.19/Branch Circuit Conductor Minimum Size
NEC 210.19 establishes minimum conductor sizing for branch circuits based on load, with the 125% continuous load requirement.
Branch circuit conductors must have an ampacity not less than the maximum load to be served. Where a branch circuit supplies continuous loads or any combination of continuous and noncontinuous loads, the minimum conductor size must have an allowable ampacity not less than the noncontinuous load plus 125 percent of the continuous load. The informational note recommends limiting voltage drop to 3 percent on branch circuits and 5 percent total (feeder plus branch).
Why this section exists
Conductors carrying continuous loads (loads expected to run for 3 hours or more) generate sustained heat that accumulates in the conductor insulation and terminations. The 125 percent multiplier provides a thermal safety margin. Without it, a conductor operating at its full rated ampacity for extended periods can overheat, especially at termination points where heat dissipation is limited.
What plan reviewers look for
Plan reviewers check conductor sizes on the panel schedule against the load for each branch circuit. For circuits with continuous loads (commercial lighting, signage, some motor loads), they verify the 125 percent multiplier has been applied before selecting the conductor size. They also check for voltage drop documentation on circuits longer than about 100 feet.
Common violations
Related NEC requirements
Section 210.3 defines branch circuit ratings. Section 215.2 has the same 125% requirement for feeder conductors. Section 240.4 covers overcurrent protection. Table 310.16 provides conductor ampacity values.