How many amps can 18 AWG wire carry?
7 A — maximum overcurrent device, NEC 240.4(D).
18 AWG copper is listed at 14 A in the 90 °C column of NEC Table 310.16, but you cannot protect it at that current: NEC 240.4(D) caps the overcurrent device at 7 A, and a continuous load at 5.6 A. It is a fixture wire, not a branch-circuit conductor.
Safety first. These figures are an educational reference before derating, not a code substitute. Verify against the current NEC and have circuits reviewed by a licensed electrician.
18 AWG ampacity — copper vs aluminum
| Material | 60 °C | 75 °C | 90 °C | Breaker cap |
|---|---|---|---|---|
| Copper | — | — | 14 A | 7 A |
| Aluminum | not rated | not rated | not rated | — |
Values are amps at a 30 °C ambient, before derating for temperature or conductor bundling. Most installations must use the 75 °C column regardless of the wire's own rating, because terminals and breakers are rated 75 °C (NEC 110.14(C)).
How far can you run 18 AWG at 7 A?
Ampacity answers whether a conductor will overheat. It says nothing about whether the voltage still arrives at the far end. Past roughly fifty feet, voltage drop is usually what really sets the wire size. These are the longest one-way runs that keep drop within the 3% recommended by the NEC 210.19(A) informational note, for 18 AWG copper carrying 7 A.
| System | Typical use | Max run at 3% | Drop at 100 ft |
|---|---|---|---|
| 120 V | standard receptacle and lighting circuits | 40 ft | 8.94 V |
| 240 V | ranges, dryers, EV chargers, feeders | 81 ft | 8.94 V |
| 12 V DC | automotive, marine, solar and battery runs | 4 ft | 8.94 V |
Single-phase, one-way distance, copper at 20 °C. Aluminum reaches its limit at roughly 60% of these distances for the same size. The 3% figure is a recommendation in an informational note, not a code requirement.
18 AWG wire size — diameter, area and resistance
Diameter
0.0403 in · 1.024 mm
Cross-section
0.823 mm² · 1,624 cmil
Nearest metric size
0.75 mm² (rounds down)
Copper resistance
6.3849 Ω per 1000 ft @ 20 °C
Aluminum resistance
10.6628 Ω per 1000 ft
Area
1.624 kcmil
Diameter is computed from the ASTM B258 definition d = 0.005 × 92^((36 − n)/39), not read from a rounded table. Resistance uses the annealed-copper constant 10.371 Ω·cmil/ft at 20 °C.
What 18 AWG wire is used for
- fixture wire and luminaire leads
- control and signalling circuits
- appliance and lamp cords
The 18 gauge mistake worth knowing
18 AWG shows 14 A in the 90 °C column of Table 310.16, but 240.4(D) limits it to a 7 A overcurrent device and 5.6 A continuous. It is a fixture wire, not a branch-circuit conductor — the table value describes the wire, not the circuit you may build with it.