What is the maximum overcurrent protection rating for a circuit of 12 AWG THHN conductors terminating on a receptacle rated at 20 amperes?

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Multiple Choice

What is the maximum overcurrent protection rating for a circuit of 12 AWG THHN conductors terminating on a receptacle rated at 20 amperes?

Explanation:
The protection for a branch circuit is limited by the lowest-rated component in that circuit. Here the receptacle is rated for 20 amperes, so the overcurrent protection cannot exceed 20 A. Even though 12 AWG THHN conductors can carry more current under the higher temperature rating they’re rated for, the device being protected (the receptacle) is 20 A, which sets the maximum size of the protective device. Therefore, the largest overcurrent protection you can use is 20 A. A smaller protection (like 15 A) is allowed, but the question asks for the maximum.

The protection for a branch circuit is limited by the lowest-rated component in that circuit. Here the receptacle is rated for 20 amperes, so the overcurrent protection cannot exceed 20 A. Even though 12 AWG THHN conductors can carry more current under the higher temperature rating they’re rated for, the device being protected (the receptacle) is 20 A, which sets the maximum size of the protective device. Therefore, the largest overcurrent protection you can use is 20 A. A smaller protection (like 15 A) is allowed, but the question asks for the maximum.

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