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What size wire for 90 amps?

3 AWG copper — at 75 °C terminals, NEC Table 310.16. Aluminum: 2 AWG.

A 90 A circuit needs 3 AWG copper, rated 100 A at 75 °C. If the run is NM-B (Romex), NEC 334.80 forces the 60 °C column and the answer becomes 2 AWG.

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.

90 amp wire size by material and terminal rating

Minimum conductor size for a 90 amp circuit by material and terminal temperature rating.
Material 60 °C (NM-B) 75 °C (typical) 90 °C
copper 2 AWG (95 A) 3 AWG (100 A) 4 AWG (95 A)
aluminum 1/0 AWG (100 A) 2 AWG (90 A) 2 AWG (100 A)

Sizes are the smallest conductor whose ampacity and NEC 240.4(D) breaker cap both reach 90 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 — 90 A becomes 112.5 A for sizing purposes. That moves this circuit to 2 AWG copper , one or more sizes above the 3 AWG the plain table suggests. EV chargers, electric heat and commercial lighting are the loads this catches most often.

How far can a 90 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 3 AWG copper at 90 A within the 3% drop recommended by the NEC 210.19(A) informational note — and what going up to 2 AWG buys you.

Maximum one-way run length for a 90 amp circuit by system voltage and conductor size.
System Typical use 3 AWG 2 AWG
120 V standard receptacle and lighting circuits 102 ft 128 ft
240 V ranges, dryers, EV chargers, feeders 203 ft 256 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 90 amp circuit

The catch at 90 amps

90 A is not a common residential breaker; 100 A almost always gets specified instead. When 90 A does appear it is usually a motor or HVAC nameplate calculation, not a panel rating.

Working the other way round? See how many amps 3 AWG carries , including its diameter, resistance and full run-length table.