NEC 310.16 Wire Sizing
What Size Wire for a 50 Amp Breaker?
The copper and aluminum conductor, ground wire, and code basis for a 50 amp circuit, per NEC Table 310.16. Common on electric ranges, welders, and NEMA 14-50 EV outlets.
Wire Size by Breaker Amperage (NEC 310.16, 75°C)
Copper and aluminum conductor and copper ground by breaker rating. Sized to the 75°C column with the 240.4(D) small-conductor limits applied.
| Breaker | Copper | Aluminum | Ground (Cu) |
|---|---|---|---|
| 20A | #12 | #10 | #12 |
| 30A | #10 | #8 | #10 |
| 40A | #8 | #8 | #10 |
| 50A | #8 | #6 | #10 |
| 60A | #6 | #4 | #10 |
| 100A | #3 | #1 | #8 |
| 200A | #3/0 | 250 kcmil | #6 |
Copper THHN/THWN-2 at the 75°C column (110.14(C)). Service and feeder ratings can use the NEC 310.12 dwelling exception. Verify terminal temperature rating and voltage drop on long runs.
How a 50 Amp Circuit Is Sized
The breaker protects the conductor, so the conductor ampacity must be at least the breaker rating (NEC 240.4). For a 50 amp breaker, the smallest 75°C copper conductor that meets or exceeds 50 amps is #8, and the aluminum equivalent is #6. For #14, #12, and #10, the 240.4(D) small-conductor rule caps the breaker at 15, 20, and 30 amps regardless of the table ampacity.
Continuous loads. If the load runs for three hours or more (an EV charger, for example), NEC 210.19(A) and 210.20(A) require sizing at 125% of the load. A load near 50 amps continuous is sized like the next circuit up, so #8 copper may need to increase a size. The chart above is for standard, non-continuous loads.
Size a Specific Circuit
Enter your load, run length, insulation, and conditions for exact NEC 310.16 sizing with temperature derating, bundling, terminal temperature limits, and voltage drop.
Frequently Asked Questions
What size wire do I need for a 50 amp breaker?
A 50 amp breaker needs #8 copper or #6 aluminum conductors, sized at the 75°C column of NEC Table 310.16 (the standard termination rating under 110.14(C)). The equipment grounding conductor is #10 copper per NEC Table 250.122. This is for a standard load; a continuous load (three hours or more) must be sized at 125%, which bumps the conductor up a size.
Can I use aluminum wire for a 50 amp breaker?
Yes. Aluminum is allowed and common on larger circuits and services where it saves on cost. For a 50 amp breaker, use #6 aluminum at the 75°C column versus #8 copper. Apply antioxidant to the terminations, torque to the listed spec, and remember aluminum drops more voltage, so check the run length on long pulls.
What size ground wire for a 50 amp breaker?
The equipment grounding conductor for a 50 amp circuit is #10 copper, per NEC Table 250.122. The EGC is sized by the breaker rating, not the circuit conductors, and it does not carry current in normal operation. If you upsize the circuit conductors for voltage drop, the EGC must be upsized proportionally per 250.122(B).
Does a continuous load change the wire size for a 50 amp circuit?
Yes. For a continuous load (one that runs for three hours or more, like an EV charger), NEC 210.19(A) and 210.20(A) require the conductor and breaker to be rated at 125% of the load. So a load pulling close to 50 amps continuously is sized like the next circuit up, and #8 copper may need to increase a size. The chart on this page is for standard (non-continuous) loads.
Do I size the wire to the breaker or to the load?
Size the conductor to the load first, then protect it with a breaker at or above the conductor rating (NEC 240.4). The breaker protects the wire, so the wire ampacity must be at least the breaker rating, with the small-conductor limits of 240.4(D) for #14, #12, and #10. On long runs, voltage drop can force a larger conductor than ampacity alone requires.
Wire Size for Other Breakers
20 Amp Wire Size
#12 copper or #10 aluminum, #12 ground.
30 Amp Wire Size
#10 copper or #8 aluminum, #10 ground.
40 Amp Wire Size
#8 copper or #8 aluminum, #10 ground.
60 Amp Wire Size
#6 copper or #4 aluminum, #10 ground.
100 Amp Wire Size
#3 copper or #1 aluminum, #8 ground.
200 Amp Wire Size
#3/0 copper or 250 kcmil aluminum, #6 ground.
Wire Size Calculator
Full NEC 310.16 sizing with derating, bundling, and terminal temperature limits.
Voltage Drop Chart
Max copper and aluminum run distances at 3% drop, for long runs.
Long run or a continuous load? Check it.
Ampacity is only half the job. A 50 amp circuit can pass the table and still fail on voltage drop over distance. Run the numbers before you pull the wire.