NEC 310.16 Wire Sizing
What Size Wire for a 200 Amp Breaker?
The copper and aluminum conductor, ground wire, and code basis for a 200 amp circuit, per NEC Table 310.16. Common on a standard modern home service.
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 | EGC (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 (75°C-listed terminals). For NM-B cable (Romex), use the 60°C column per NEC 334.80 and 110.14(C)(1)(a). Service and feeder ratings can use the NEC 310.12 dwelling exception. Verify terminal temperature rating and voltage drop on long runs.
How a 200 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 200 amp breaker, the smallest 75°C copper conductor that meets or exceeds 200 amps is 3/0, and the aluminum equivalent is 250 kcmil. 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.
The dwelling exception (NEC 310.12). A single-phase dwelling service or main power feeder can be sized at 83% of the rating, because a home rarely draws its full service continuously. That is why a 200 amp home service commonly runs 2/0 copper or 4/0 aluminum instead of the 3/0 copper a 200 amp branch circuit would require. Confirm your load with a service calculation before you rely on the exception.
Size a Specific Circuit
Enter your load, run length, insulation, and conditions for NEC 310.16 sizing with temperature derating, bundling, and terminal temperature limits; the result links to the voltage drop calculator, which checks that wire over your run; this tool does not size for voltage drop. It opens on a 200 A load at the 75°C column, the feeder answer above. It does not apply the dwelling service rule, so it will not return the smaller service size.
Frequently Asked Questions
What size wire do I need for a 200 amp breaker?
A 200 amp single-phase dwelling service needs 2/0 copper or 4/0 aluminum under the NEC 310.12 dwelling allowance (conductors rated for 83% of the service rating). Its grounding electrode conductor is #4 copper, sized from the service conductors per NEC Table 250.66. A 200 amp feeder that is not a dwelling service is sized at the 75°C column of Table 310.16 (3/0 copper) and grounded by a #6 copper equipment grounding conductor per Table 250.122.
Can I use aluminum wire for a 200 amp breaker?
Yes. Aluminum is allowed and common on larger circuits and services where it saves on cost. For a 200 amp breaker, use 250 kcmil aluminum at the 75°C column versus 3/0 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 200 amp breaker?
It depends on whether this is a service or a feeder. For a 200 amp dwelling service, the grounding electrode conductor (GEC) is #4 copper or #2 aluminum, sized from the service-entrance conductors per NEC Table 250.66 (not by the breaker). If this 200 amp panel is instead a subpanel fed by a feeder, the equipment grounding conductor run with the feeder is #6 copper per NEC Table 250.122. A service uses a GEC to the grounding electrodes; a feeder or branch circuit uses a 250.122 EGC.
Why can a 200 amp service use smaller wire than a 200 amp branch circuit?
NEC 310.12 lets a single-phase dwelling service or main power feeder use conductors rated for 83% of the service rating, because a whole house rarely draws its full rating continuously. That is why a 200 amp home service commonly uses 2/0 copper or 4/0 aluminum instead of the 3/0 copper a 200 amp branch circuit would need. The exception applies only to dwelling services and main feeders, not general branch circuits.
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 copper ground (#10 aluminum).
30 Amp Wire Size
#10 copper or #8 aluminum, #10 copper ground (#8 aluminum).
40 Amp Wire Size
#8 copper or #8 aluminum on 75°C-marked terminations (#8 copper or #6 aluminum at 60°C or on NM-B), #10 copper ground (#8 aluminum).
50 Amp Wire Size
#8 copper or #6 aluminum on 75°C-marked terminations (#6 copper or #4 aluminum at 60°C or on NM-B), #10 copper ground (#8 aluminum).
60 Amp Wire Size
#6 copper or #4 aluminum on 75°C-marked terminations (#4 copper or #3 aluminum at 60°C or on NM-B), #10 copper ground (#8 aluminum).
100 Amp Wire Size
#3 copper or #1 aluminum on 75°C-marked terminations (#1 copper or 1/0 aluminum at 60°C or on NM-B), #8 copper ground (#6 aluminum).
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 200 amp circuit can pass the table and still fail on voltage drop over distance. Run the numbers before you pull the wire.