Three columns, three answers
NM-B cable is held to the 60 °C column, THHN in conduit on 60/75 °C breakers uses 75 °C. That is why 14 AWG NM-B and 14 AWG THHN can both serve 15 A.
What size wire for 15 amps?
A 15 A circuit takes 14 AWG NM-B in the wall or 14 AWG copper THHN in conduit (75 °C), with a 14 AWG ground; aluminum needs 12 AWG. At an 12 A load the copper reaches 95 ft at 240 V (3 % drop). Used for general lighting and bedroom receptacles.
02 · Ampacity · NEC 2023 Table 310.16
14 AWG copper · 90 °C insulation, 75 °C terminals, 30 °C, 3 conductors
USE:
14 AWG COPPER · 20 A ALLOWABLE · 15 A MAX BREAKER
Allowable
20 A
14 AWG Cu
Max breaker
15 A
240.4(D) cap
For your load
14 AWG
15 A
14 AWG copper carries 25 A after derating from the 90 °C column and 20 A at its 75 °C terminals, so it is good for 20 A on a breaker up to 15 A.
- Meets NEC 2023 Table 310.16 at 75°C — verify with your local AHJ/inspector110.14(C)
- Load 15 A ≤ 20 A310.14
Derating math
- Table 310.16 at 90 °C
- 25 Aderating starts at the insulation rating
- Ambient factor
- × 1.0030 °C, Table 310.15(B)(1)
- Bundling factor
- × 1.003 current-carrying conductors, 310.15(C)(1)
- Derated
- 25 A
- Terminal limit (75 °C)
- 20 A110.14(C)
- Allowable
- 20 Athe terminals decide
14 AWG
- Copper 60 / 75 / 90 °C
- 15 / 20 / 25 ANM-B uses the 60 °C column (334.80)
- Aluminum 60 / 75 / 90 °C
- —
- Largest breaker (Cu, 75 °C)
- 15 A240.4(D) small-conductor cap
- Solid diameter
- 0.0641"1.628 mm · ASTM B258 formula
- Stranded (7 strands)
- 0.0730"1.854 mm · Table 8
- THHN outside
- 0.111"2.82 mm · 0.0097 in² · Table 5
- Area
- 4,110 cmil2.08 mm² · nearest IEC 2.5 mm²
- DC resistance, 75 °C
- 3.14 Ω/1000 ftaluminum 5.17 Ω/1000 ft · Table 8
- Copper weight
- 12.4 lb/1000 ft
15 A circuit at a glance
Wire
- Copper NM-B (60 °C)
- 14 AWG
- Copper THHN (75 °C)
- 14 AWG
- Aluminum (75 °C)
- 12 AWG
Ground & breaker
- Copper ground
- 14 AWG
- Aluminum ground
- 12 AWG
- Continuous load max
- 12 A
- Breaker
- 15 A
Distance (3 %)
- Cu at 120 V, 12 A
- 47 ft
- Cu at 240 V, 12 A
- 95 ft
- Al at 240 V, 12 A
- 92 ft
15 A circuit tables 7 rows
Sort any column, print a shop sheet, download CSV. Click a row to load it in the calculator.
| Actions | |||||
|---|---|---|---|---|---|
| 14 AWG | 14 AWG | 14 AWG | 95 ft | ||
| 14 AWG | 14 AWG | 14 AWG | 95 ft | ||
| 12 AWG | 12 AWG | 12 AWG | 92 ft |
Feet one way (the current goes out and back). Ampacity is a separate check: a long run may need a heavier wire for drop, never a lighter one for heat.
05 / Field guide
15 amps:
which wire, which method.
A 15 A circuit takes 14 AWG NM-B in the wall or 14 AWG copper THHN in conduit (75 °C), with a 14 AWG ground; aluminum needs 12 AWG. At an 12 A load the copper reaches 95 ft at 240 V (3 % drop). Used for general lighting and bedroom receptacles.
Breaker rules
240.4(D) fixes the small sizes: 14 AWG on 15 A, 12 AWG on 20 A, 10 AWG on 30 A, whatever the ampacity table allows.
Distance
The answer above is the minimum for heat. On a long run upsize for voltage drop, and grow the ground with it: the table below gives the longest 240 V run at 3 % for each candidate size.
Questions
Answered plainly.
01What size wire for a 15 amp breaker?
+−
14 AWG copper NM-B in the wall, 14 AWG copper THHN in conduit or 12 AWG aluminum, all with ampacity at least 15 A (NEC 2023 Table 310.16).
02Can I use 14 AWG wire on a 15 amp breaker in NM-B cable?
+−
Yes: 14 AWG NM-B is rated 15 A at 60 °C.
03What size ground wire for 15 amps?
+−
14 AWG copper or 12 AWG aluminum (Table 250.122), larger in proportion if the circuit wire is upsized for distance (250.122(B)).
04How far can I run a 15 amp circuit?
+−
At 12 A (80 %) on 14 AWG copper, 95 ft one way at 240 V or 47 ft at 120 V before the drop passes 3 %. Beyond that, go up a size.
05What is the largest continuous load on a 15 amp circuit?
+−
12 A: a continuous load (3 hours or more) may use only 80 % of the breaker rating (the 125 % rule).