What Size Wire for a 90 Amp Breaker?
A 90 A breaker needs 3 AWG copper or 2 AWG aluminum with 75°C terminations (NEC Table 310.16). Longer runs may need a size up for voltage drop: distances below.
Minimum wire size for 90 amps
| Application | Copper (75°C) | Aluminum (75°C) |
|---|---|---|
| Branch circuit / feeder (Table 310.16) | 3 AWG | 2 AWG |
Assumes 75°C-rated terminations (NEC 110.14(C)). Both assume no more than three current-carrying conductors in a raceway at 30°C ambient. Derating, continuous loads, and local amendments can change the answer: confirm with a licensed electrician.
Ground wire for 90 amps
| Ground | Copper | Aluminum |
|---|---|---|
| Equipment ground (bare / green) (Table 250.122) | 8 AWG | 6 AWG |
The equipment ground is sized by the breaker, not the load: a 90A breaker falls in Table 250.122's 100 A row. Upsize the hots for voltage drop and the ground must grow in proportion (NEC 250.122(B)). Every size, with a worked upsizing example, is in the ground wire size chart.
How far can you run it? (voltage drop)
Keeping voltage drop under the recommended 3% at a 72 A load (80% of the breaker), 3 AWG copper is good for roughly:
| System voltage | Max one-way run (3 AWG Cu) |
|---|---|
| 240 V | ≈ 203 ft |
Past these distances, step up one gauge. Run your exact length and load through the voltage drop calculator.
What runs on 90 amps
- Subpanel feeder
- Large tankless water heater sub-circuits
Parts for a 90 A circuit
Before touching a 90 A circuit, confirm it is dead with a voltage pen; a clamp meter reads the real load on one of its conductors.
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Non-contact voltage tester
Klein Tools NCVT-3P
Best for: Confirming a circuit is dead before you open a device or box
Clamp meter
Fluke 323
Best for: Measuring what a hardwired circuit actually draws, even in a crowded panel
Frequently asked questions
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