According to the NEC, what is the ampacity of a 12 AWG TW copper conductor and the limit of overcurrent protection?

The ampacity of a conductor refers to the maximum amount of electric current it can carry before sustaining immediate or long-term damage. According to the National Electrical Code (NEC), a 12 AWG (American Wire Gauge) TW (Thermoplastic Insulated Wire) copper conductor has a standard ampacity of 20 amperes under typical installations.

The limit of overcurrent protection is directly related to the conductor's ampacity, ensuring that the circuit is adequately protected from overloads and potential overheating. In the case of a 12 AWG copper conductor, the NEC allows for a maximum overcurrent protection device (breaker or fuse) rated at 20 amps. This matches the ampacity, reinforcing the requirement that the protective device should not exceed the conductor’s safe carrying capacity to prevent any risk of fire or damage.

Choosing an overcurrent protection device rated higher than 20 amps would violate safety standards as it could lead to the conductor carrying a load beyond its rated capacity, thereby increasing the risk of overheating. Thus, the appropriate pairing of a 12 AWG TW copper conductor being rated for 20 amps and its overcurrent protection limit also set at 20 amps establishes the correct answer in this scenario.