Wire Ampacity Chart & Reference Lookup

Interactive NEC Table 310.16 & Table 310.17 wire ampacity chart with ambient temperature and conduit bundling adjustment calculators.

NEC edition

Inputs

§110.14(C): the final ampacity may not exceed the conductor ampacity at the termination rating

The correction factor comes from the 90°C column of Table 310.15(B)(1), which is the column the derating starts in.

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⚡ Test your knowledge
NEC Article 220 was renumbered in the 2026 code cycle. What is the new article number?
  • A. Art. 100
  • B. Art. 120
  • C. Art. 200
  • D. Art. 230
💡 NEC 2026 renumbered Article 220 (Branch-Circuit, Feeder, and Service Calculations) to Article 120.
Energy Management Systems were moved from Article 750 to which article in NEC 2026?
  • A. Art. 100
  • B. Art. 125
  • C. Art. 130
  • D. Art. 150
💡 NEC 2026 moved Energy Management Systems from Article 750 to Article 130.
Which NEC standard size overcurrent device comes after 90A?
  • A. 95A
  • B. 100A
  • C. 110A
  • D. 105A
💡 Per NEC §240.6(A), the standard sizes are …90, 100, 110, 125… There is no 95A standard size.

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How it works & the NEC rules behind it

NEC Table 310.16 is the fundamental conductor ampacity table used daily across electrical construction. Sizing a conductor correctly requires navigating three temperature columns and terminal ratings.

Three Pillars of Conductor Ampacity:

  • 1. The 90°C Derating Advantage (§110.14(C)): While equipment terminal lugs are almost universally rated for 75°C (or 60°C for ≤ 100A), you are permitted to start bundling and ambient temperature derating calculations from the higher 90°C column (THHN / XHHW-2), as long as the final ampacity does not exceed the 75°C terminal rating!
  • 2. Small Conductor Rule (§240.4(D)): Overcurrent protection cannot exceed:
    • #14 AWG Copper: 15 Amps
    • #12 AWG Copper: 20 Amps
    • #10 AWG Copper: 30 Amps.
  • 3. Table 310.16 (Raceway) vs. Table 310.17 (Free Air): Conductors in free air (single conductors on insulators or outdoor open wiring) carry substantially more current due to natural convection.

Formulas & equations

Adjusted Ampacity = Table 310.16 (90°C) × Temp Correction Factor × Bundling Factor Max Allowable Circuit Current = Min(Adjusted Ampacity, Terminal 75°C/60°C Ampacity)

NEC reference table

Wire Gauge Copper 60°C (TW/NM-B) Copper 75°C (THWN) Copper 90°C (THHN/XHHW) Aluminum 75°C Aluminum 90°C
#14 AWG15 A20 A25 A——
#12 AWG20 A25 A30 A20 A25 A
#10 AWG30 A35 A40 A30 A35 A
#8 AWG40 A50 A55 A40 A45 A
#6 AWG55 A65 A75 A50 A60 A
#4 AWG70 A85 A95 A65 A75 A
#2 AWG95 A115 A130 A90 A100 A
#1/0 AWG125 A150 A170 A120 A135 A
#2/0 AWG145 A175 A195 A135 A150 A
#3/0 AWG165 A200 A225 A155 A175 A
#4/0 AWG195 A230 A260 A180 A205 A
250 kcmil215 A255 A290 A205 A230 A
500 kcmil320 A380 A430 A310 A350 A

*Source: NEC Table 310.16 (Ampacities of Insulated Conductors in Raceway or Cable, based on 30°C / 86°F ambient).

Worked example, step by step

Example: Derating #6 AWG THHN Copper in 105°F Attic with 6 Current-Carrying Wires

Wire: #6 AWG THHN Copper (90°C Base = 75A), 105°F (41°C) ambient, 6 conductors in conduit.

  • 1. 90°C Base Ampacity: 75 Amps (Table 310.16).
  • 2. Ambient Temp Correction: 105°F falls in 41°C–45°C tier = 0.87 factor (Table 310.15(B)(1)).
  • 3. Bundling Adjustment: 6 conductors = 0.80 factor (Table 310.15(C)(1)).
  • 4. Adjusted Ampacity: 75A × 0.87 × 0.80 = 52.2 Amps.
  • 5. Terminal Check: 52.2A is less than 75°C terminal rating (65A). Wire can carry 52.2 Amps (use standard 50A breaker).

Frequently asked questions

Under NEC §334.80, Type NM-B nonmetallic-sheathed cable conductor ampacity must comply with the 60°C temperature rating (e.g. 55A for #6 Cu, rather than 75A). However, the 90°C rating is permitted to be used for bundling and ambient derating calculations, provided the final value does not exceed the 60°C rating.

Table 310.17 applies ONLY to single insulated conductors operating in free air (such as open overhead spans, open-bottom cable tray single conductors with 1-diameter spacing, or meter base mast entries exposed to outdoor airflow).

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