Which THHN/THWN copper conductor is the smallest size permitted for a feeder with a 200-amp breaker in a single-family dwelling?

Which THHN/THWN copper conductor is the smallest size permitted for a feeder with a 200-amp breaker in a single-family dwelling?

• A. 2/0 AWG
• B. 1 AWG
• C. 1/0 AWG
• D. 4/0 AWG

Answer: (A)

The key idea is sizing the feeder conductors to handle the breaker rating using the NEC ampacity tables. For THHN/THWN copper, you typically use the 75°C ampacity column (assuming the panel terminals and equipment are rated 75°C), and you must choose a conductor whose ampacity is at least as large as the feeder/breaker rating. For a 200-amp feeder, you need a conductor with an ampacity of 200 A or more. Among the given copper sizes, the smallest one that meets or exceeds 200 A on the 75°C column is the 2/0 AWG size. The next smaller option, 1/0 AWG, does not reach 200 A, so it would not be allowed for a 200 A feeder. The larger size is more than sufficient but not necessary for this requirement. Remember that the 200 A breaker rating sets the requirement, and the conductor must be able to carry that load safely, which is why the 2/0 size is the minimum in this scenario. If the equipment were limited to a lower temperature rating, you’d have to re-check the applicable column, but with typical modern dwelling gear rated for 75°C, 2/0 is the smallest acceptable size here.

The key idea is sizing the feeder conductors to handle the breaker rating using the NEC ampacity tables. For THHN/THWN copper, you typically use the 75°C ampacity column (assuming the panel terminals and equipment are rated 75°C), and you must choose a conductor whose ampacity is at least as large as the feeder/breaker rating.

For a 200-amp feeder, you need a conductor with an ampacity of 200 A or more. Among the given copper sizes, the smallest one that meets or exceeds 200 A on the 75°C column is the 2/0 AWG size. The next smaller option, 1/0 AWG, does not reach 200 A, so it would not be allowed for a 200 A feeder. The larger size is more than sufficient but not necessary for this requirement.

Remember that the 200 A breaker rating sets the requirement, and the conductor must be able to carry that load safely, which is why the 2/0 size is the minimum in this scenario. If the equipment were limited to a lower temperature rating, you’d have to re-check the applicable column, but with typical modern dwelling gear rated for 75°C, 2/0 is the smallest acceptable size here.