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Conductor Ampacity Reference

Reference Equipment Updated Aug 24, 2026 · Electrical

Overview

Conductor ampacity (max current a wire can safely carry) determines what size breaker can protect a given wire and what size wire is required for a given load. Picking wrong oversizes (waste) or undersizes (fire). This reference is the field card.

Reference Table

Copper conductors, 60°C / 75°C / 90°C insulation, NEC Table 310.16:

Wire size (AWG) 60°C (TW/UF) 75°C (THW/THWN/USE) 90°C (THHN/THWN-2/XHHW-2)
14 15 A 20 A 25 A
12 20 A 25 A 30 A
10 30 A 35 A 40 A
8 40 A 50 A 55 A
6 55 A 65 A 75 A
4 70 A 85 A 95 A
3 85 A 100 A 115 A
2 95 A 115 A 130 A
1 110 A 130 A 145 A
1/0 125 A 150 A 170 A
2/0 145 A 175 A 195 A
3/0 165 A 200 A 225 A
4/0 195 A 230 A 260 A

Important: the column you size from is set by the terminations, not by the wire's insulation. NEC 110.14(C)(1) splits it at 100 A: equipment rated 100 A or less (or marked for 14 AWG through 1 AWG conductors) uses the 60°C column unless the equipment is listed for higher, and equipment rated over 100 A (or marked for conductors larger than 1 AWG) uses the 75°C column. So a 15 A or 20 A branch circuit lands on 60°C, while a 100 A or 200 A feeder or service lands on 75°C. The 90°C column is for derating math only.

Aluminum conductors (residential service entrance only):

Wire size (AWG) 60°C 75°C 90°C
6 40 A 50 A 55 A
4 55 A 65 A 75 A
2 75 A 90 A 100 A
1/0 100 A 120 A 135 A
2/0 115 A 135 A 150 A
4/0 150 A 180 A 205 A

Aluminum branch circuits (smaller than 6 AWG, used 1965 - 1973) are NOT in current use for new construction.

Specifications

Common residential applications + correct conductor:

Load Conductor Breaker
15A general-use circuit 14 AWG copper 15A
20A general-use circuit 12 AWG copper 20A
30A dryer / water heater 10 AWG copper 30A
40A range / oven 8 AWG copper 40A
50A range / EV charger 6 AWG copper 50A
60A sub-panel feeder 6 AWG copper or 4 AWG aluminum 60A
100A sub-panel feeder 3 AWG copper or 1 AWG aluminum 100A
200A service entrance 2/0 copper or 4/0 aluminum 200A

Performance - Derating

Ampacity rated above is for ambient up to 30°C. Above that, derate:

Correction factors are specific to the conductor's insulation rating, so the column matters. Listed below for the 75°C column, with the 60°C and 90°C values in parentheses (NEC Table 310.15(B)(1)):

  • 31 - 35°C (88 - 95°F): multiply by 0.94 (60°C: 0.91, 90°C: 0.96)
  • 36 - 40°C (97 - 104°F): multiply by 0.88 (60°C: 0.82, 90°C: 0.91)
  • 41 - 45°C (106 - 113°F): multiply by 0.82 (60°C: 0.71, 90°C: 0.87)
  • 46 - 50°C (115 - 122°F): multiply by 0.75 (60°C: 0.58, 90°C: 0.82)

When 4+ current-carrying conductors share a conduit, apply NEC 310.15(C)(1) adjustment factors (also derating).

Safety

Sizing a branch circuit to its 90°C column is almost always a code violation because the receptacle, breaker, or termination is 60°C-rated. The conductor's max ampacity is the lowest rating in the entire current path - wire / lug / breaker / device. On equipment rated 100 A or less, default to the 60°C column unless the termination listing explicitly allows higher; over 100 A, 75°C is the normal column. The 90°C column is only a starting point for ambient and bundling derating, never the final answer.

Notes

  • Voltage drop: ampacity is the safety limit, NOT the performance limit. For long runs (over 50 ft on 15A circuits, over 100 ft on 20A), check voltage drop separately. 3 % drop is the NEC recommendation for branch circuits.
  • Aluminum service entrance is common + acceptable, sized one wire-size LARGER than copper for the same ampacity.
  • AC vs DC: this table is AC. DC + solar systems use different tables; consult NEC Article 690.
  • The "use 12 AWG everywhere" practice: some shops install 12 AWG on every circuit regardless. This isn't required but isn't a violation. Use as a marketing differentiator if it's your shop's standard.

References

  • NEC Article 310 (Conductors for General Wiring)
  • NEC Tables 310.16 + 310.17 + 310.20
  • IEEE residential voltage-drop guidance

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