How many amps can 4 AWG wire carry?
85 A — copper at 75 °C, NEC Table 310.16.
4 AWG copper carries 85 A at 75 °C, 70 A at 60 °C and 95 A at 90 °C under NEC Table 310.16, before derating. Aluminum at the same size is 65 A at 75 °C.
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.
4 AWG ampacity — copper vs aluminum
| Material | 60 °C | 75 °C | 90 °C | Breaker cap |
|---|---|---|---|---|
| Copper | 70 A | 85 A | 95 A | — |
| Aluminum | 55 A | 65 A | 75 A | — |
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 4 AWG at 85 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 4 AWG copper carrying 85 A.
| System | Typical use | Max run at 3% | Drop at 100 ft |
|---|---|---|---|
| 120 V | standard receptacle and lighting circuits | 85 ft | 4.22 V |
| 240 V | ranges, dryers, EV chargers, feeders | 170 ft | 4.22 V |
| 12 V DC | automotive, marine, solar and battery runs | 9 ft | 4.22 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.
4 AWG wire size — diameter, area and resistance
Diameter
0.2043 in · 5.189 mm
Cross-section
21.151 mm² · 41,741 cmil
Nearest metric size
25 mm² (rounds up)
Copper resistance
0.2485 Ω per 1000 ft @ 20 °C
Aluminum resistance
0.4149 Ω per 1000 ft
Area
41.741 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 4 AWG wire is used for
- 85 A circuits
- 100 A aluminum subpanel feeders
- hot tubs and spa panels
The 4 gauge mistake worth knowing
4 AWG aluminum is the standard 100 A subpanel feeder in many jurisdictions even though its 75 °C ampacity is only 65 A — because 100 A feeders are permitted to use the 310.12 dwelling-service table rather than 310.16. This exception is why 4 AWG looks undersized on a plain ampacity chart.