Branch-circuit wire size and minimum ampacity
Branch-circuit wires must have an ampacity at least equal to the larger of two values: the noncontinuous load plus 125% of the continuous load, or the maximum load after adjustment and correction factors.
What the code requires
Section 210.19 sets the minimum size and ampacity of branch-circuit conductors, the wiring that runs from a circuit's breaker or fuse to its outlets and equipment. It applies to circuits up to 1000 V ac or 1500 V dc.
The conductor ampacity must be at least the larger of two numbers. The first is the noncontinuous load plus 125% of the continuous load. The second is the maximum load once the code's adjustment and correction factors are applied. The conductor terminations must also comply with 110.14(C).
The 2023 NEC reorganized this section. The former 210.19(A)(1) through (A)(4) are now 210.19(A) through (D), and the dividing line moved from 600 V to 1000 V ac or 1500 V dc. Rules for branch circuits above that level moved to new Article 235, which covers branch circuits, feeders and services over 1000 V ac or 1500 V dc.
On the job
- Terminal temperature ratings limit conductor ampacity under 110.14(C). Where terminals are rated 75°C, a conductor with a 90°C rating is still limited to its 75°C ampacity at those terminals.
- Run both checks. A circuit that passes the 125% check can still need larger wire once adjustment or correction factors are applied.
- Section 210.19 has further subsections, (B) through (D), that this page does not cover. Your electrician should confirm whether any of them apply to the specific load.
Exceptions that matter
- If the assembly and its overcurrent devices are listed for operation at 100% of their rating, the conductors may be sized for the continuous plus noncontinuous load, without the 125% factor.
- A run between separately installed pressure connectors may also be sized at the continuous plus noncontinuous load, as long as that run does not extend into the supply or load enclosure.
Related sections
- NEC 210.20
- NEC 210.21
- NEC 210.24
- NEC 110.14(C)
- NEC 310.15: Derating wire for heat and crowded conduits
- NEC 215.2: Feeder wire size and minimum ampacity
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Kyle Robert Anderson KBC Electric · CSLB #1073066 · C-10 Electrical · Licensed since 2021