What is the maximum overcurrent protection rating for a circuit with 12 AWG THHN conductors terminating on a 20-ampere receptacle?

The maximum overcurrent protection rating for a circuit with 12 AWG THHN conductors is 20 amperes. This is aligned with the National Electrical Code (NEC) guidelines, which dictate that 12 AWG copper conductors are typically rated for a maximum continuous load of 20 amps.

In this situation, the conductors are sufficiently sized to handle that load without overheating or becoming a safety hazard. Using a 20-ampere breaker matches the receptacle's rating, ensuring proper protection and functioning.

When selecting an overcurrent protection device, it is essential to ensure that it does not exceed the allowable ampacity for the conductor size, which is why a rating of 20 amps is the appropriate choice here. Other ratings such as 15 amps, 25 amps, or 30 amps do not comply with the conductor's ampacity and could lead to improper circuit operation or potential safety issues.