What size wire for 70 amps?
4 AWG copper — at 75 °C terminals, NEC Table 310.16. Aluminum: 3 AWG.
A 70 A circuit needs 4 AWG copper, rated 85 A at 75 °C. NM-B cable at the 60 °C column gives the same answer.
Safety first. This is a starting point before derating, not a load calculation. Wire sizing affects fire and shock safety — verify against the current NEC and have circuits designed or reviewed by a licensed electrician for your jurisdiction.
70 amp wire size by material and terminal rating
| Material | 60 °C (NM-B) | 75 °C (typical) | 90 °C |
|---|---|---|---|
| copper | 4 AWG (70 A) | 4 AWG (85 A) | 6 AWG (75 A) |
| aluminum | 2 AWG (75 A) | 3 AWG (75 A) | 4 AWG (75 A) |
Sizes are the smallest conductor whose ampacity and NEC 240.4(D) breaker cap both reach 70 A, before any derating. Use the 75 °C column unless every terminal, breaker and device in the circuit is rated otherwise (NEC 110.14(C)).
If the load runs continuously
A load operating for three hours or more is a continuous load, and NEC 210.19(A)(1) requires the conductor to be sized at 125% of it — 70 A becomes 87.5 A for sizing purposes. That moves this circuit to 3 AWG copper , one or more sizes above the 4 AWG the plain table suggests. EV chargers, electric heat and commercial lighting are the loads this catches most often.
How far can a 70 amp circuit run?
The table above only prevents overheating. On a long run the limit is voltage arriving at the far end, and it bites well before ampacity does. These are the longest one-way runs for 4 AWG copper at 70 A within the 3% drop recommended by the NEC 210.19(A) informational note — and what going up to 3 AWG buys you.
| System | Typical use | 4 AWG | 3 AWG |
|---|---|---|---|
| 120 V | standard receptacle and lighting circuits | 103 ft | 131 ft |
| 240 V | ranges, dryers, EV chargers, feeders | 207 ft | 261 ft |
| 12 V DC | automotive, marine, solar and battery runs | 10 ft | 13 ft |
Single-phase, one-way distance, copper at 20 °C. Aluminum reaches its limit at roughly 60% of these distances. The 3% target is a recommendation, not a code requirement.
What runs on a 70 amp circuit
- subpanels
- large air handlers
- commercial equipment feeders
The catch at 70 amps
70 A is the size where a strict ampacity reading and the Code disagree. 6 AWG copper tops out at 65 A, so a chart says 4 AWG — but 65 A is not a standard breaker rating, and NEC 240.4(B) permits rounding up to the next standard size (70 A) on a feeder that does not supply receptacles for portable loads. Both answers can be correct; which one applies depends on what the circuit feeds.
Working the other way round? See how many amps 4 AWG carries , including its diameter, resistance and full run-length table.