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What size wire for 30 amps?

10 AWG copper — at 75 °C terminals, NEC Table 310.16. Aluminum: 8 AWG.

A 30 A circuit needs 10 AWG copper, rated 35 A at 75 °C with a 30 A breaker cap under 240.4(D). 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.

30 amp wire size by material and terminal rating

Minimum conductor size for a 30 amp circuit by material and terminal temperature rating.
Material 60 °C (NM-B) 75 °C (typical) 90 °C
copper 10 AWG (30 A) 10 AWG (35 A) 10 AWG (40 A)
aluminum 8 AWG (35 A) 8 AWG (40 A) 8 AWG (45 A)

Sizes are the smallest conductor whose ampacity and NEC 240.4(D) breaker cap both reach 30 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 — 30 A becomes 37.5 A for sizing purposes. That moves this circuit to 8 AWG copper , one or more sizes above the 10 AWG the plain table suggests. EV chargers, electric heat and commercial lighting are the loads this catches most often.

How far can a 30 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 10 AWG copper at 30 A within the 3% drop recommended by the NEC 210.19(A) informational note — and what going up to 8 AWG buys you.

Maximum one-way run length for a 30 amp circuit by system voltage and conductor size.
System Typical use 10 AWG 8 AWG
120 V standard receptacle and lighting circuits 60 ft 96 ft
240 V ranges, dryers, EV chargers, feeders 120 ft 191 ft
12 V DC automotive, marine, solar and battery runs 6 ft 10 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 30 amp circuit

The catch at 30 amps

30 A is 10 AWG copper — and 10 AWG is the largest conductor still capped by 240.4(D), so its 35 A table rating is unusable. 30 A is the ceiling.

Working the other way round? See how many amps 10 AWG carries , including its diameter, resistance and full run-length table.