14 AWG NM-B Copper Ampacity & Derating
NEC Quick Answer
14 AWG NM-B copper is limited to 15A. Although the conductors inside NM-B cable are rated 90C, NEC 334.80 restricts NM-B to the 60C ampacity column. The maximum overcurrent protection is 15A per NEC 240.4(D). Note: a lower AWG number means a thicker wire, so 10 AWG is thicker than 14 AWG and carries more current.
NEC 2023: Table 310.16 (60C column), Section 334.80, Section 240.4(D)
Calculation Walkthrough
Per NEC 2023 Table 310.16, 14 AWG copper NM-B (90°C column) = 25A base. Assumes ≤3 CCC at 30°C ambient.
At 30.0°C (86°F), factor = 1.0. No reduction. At 50°C attic: factor drops to ~0.82 for 60°C insulation.
≤3 CCC = factor 1.0. EGC + neutral (unbalanced) not counted per 310.15(E). Typical 240V circuit: 2 hots + N + G = 2 CCC.
Equipment termination governs the final ampacity. Circuits ≤100A: use 60°C column unless conductor + equipment both rated 75°C. Modern panels and breakers are listed for 60°C terminations, so the 60°C column value of 15A becomes the ceiling. The 90°C rating is only used as the starting point for temperature correction and bundling derating. After all adjustments, the result cannot exceed the termination column value. This is the single most commonly failed inspection item.
NEC recommends limiting voltage drop to 3% on branch circuits and 5% total (branch + feeder combined). For 14 AWG copper carrying 15A at 240V single-phase over a 100-foot one-way run: Vd = (2 × L × I × R) / 1000. The resistance per 1000 ft for 14 AWG copper at 75°C is used from NEC Chapter 9 Table 8. At 15A and 100 ft, the drop is 9.4V (3.9%). For longer runs or higher loads, use the voltage drop calculator with your specific distance and load.
Common Applications
14 AWG NM-B copper at 15A covers general-purpose 15A lighting and receptacle circuits in residential and light commercial work. Paired with a 15A breaker, this is the minimum wire size permitted for branch circuits under NEC 240.4(D). Typical installations include bedroom and living room lighting, hallway receptacles, and switched outlets. In conduit runs, 14 AWG Copper NM-B handles multiple circuits per conduit without derating concerns when limited to 3 current-carrying conductors. For 20A circuits, upsize to 12 AWG. Note that some jurisdictions require 12 AWG minimum for all branch circuits regardless of load, so check your state adoption status.
NEC 2020 vs NEC 2023
Ampacity values for 14 AWG copper are identical across NEC 2017, 2020, and 2023 editions. The only change affecting this conductor is the table renumbering from Table 310.15(B)(16) to Table 310.16 in the 2023 edition. This renumbering was part of a broader reorganization of Article 310 that also moved temperature correction factors from Table 310.15(B)(2)(a) to Table 310.15(B)(1) and bundling adjustment factors from Table 310.15(B)(3)(a) to Table 310.15(C)(1). When citing NEC references on permits or inspection reports, use the table numbers that match your state's adopted code year. States on NEC 2020 or earlier should cite Table 310.15(B)(16); states that have adopted NEC 2023 should cite Table 310.16.
Quick Reference
| Conductor | Temp | Amps | Use |
|---|---|---|---|
| 14 AWG Copper TW | 60°C | 15A | Wet / underground |
| 14 AWG Copper THW | 75°C | 20A | Standard circuits |
| 14 AWG Copper THHN | 90°C | 25A | Derating start only |
| 14 AWG Copper free air | 75/90°C | 30A / 35A | Table 310.17 |
Frequently asked questions
What is the ampacity of 14 AWG Copper wire?
14 AWG NM-B Copper has a base ampacity of 25A at 90°C per NEC 2023 Table 310.16. After applying the 110.14(C) termination temperature limit, the usable ampacity is 15A for most installations. This is the value you use for circuit sizing and breaker selection.
What size breaker do I need for 14 AWG copper wire?
Pair 14 AWG copper with a 15A breaker. The wire's usable ampacity of 15A must equal or exceed the breaker rating. For continuous loads (running 3+ hours), the load must not exceed 80% of the breaker rating (12A on a 15A breaker). See the full ampacity table for all wire sizes.
Can I use 14 AWG wire in conduit?
NM-B cable can be sleeved through short sections of conduit for physical protection per NEC 334.15(B), but it is not a standard conduit wiring method. For conduit installations, use individual THHN or XHHW-2 conductors instead. See Romex vs conduit and 14 AWG THHN for conduit ampacity.
How far can I run 14 AWG copper wire?
The maximum distance depends on load and voltage. For 14 AWG copper at 15A on a 240V circuit, use the voltage drop calculator with your specific distance. As a rule of thumb, keep voltage drop under 3% for branch circuits. Longer runs may require upsizing the conductor.
Common products for 14 AWG Copper circuits
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NEC 2023 references verified April 2026