Use of 20 Amp Breaker and 12/2 Cable for Circuit Containing 15 Amp Duplex Receptacles

Question

What is the rationale behind using a 20 amp circuit breaker with 12/2 cable for a circuit that only contains 15 amp duplex receptacles? I understand the rationale behind using 12/2 cable instead of 14/2 cable, but do not understand the rationale behind using the 20 amp circuit breaker instead of a 15 amp circuit breaker. Without understanding the rationale, I would assume it would be prudent to either:

1. Replace the 20 amp circuit breaker with a 15 amp circuit breaker.
2. Replace the 15 amp duplex receptacles with 20 amp duplex receptacles.

References to the National Electric Code would be appreciated.

Edit:

I did not intended to ask if it was permissible to use a 20 amp circuit breaker. Instead, I meant to ask "What benefit does the 20 amp circuit breaker provide if there are only 15 amp duplex receptacles?"

Answer 1

The 20 amp circuit breaker with 12/2 cable and 15 amp duplex receptacles allows for a total sustainable power consumption of 1,920 watts (20 amp x 80% x 120 volts) as opposed to 1,440 watts (15 amp x 80% x 120 volts). Thus, the 20 amp circuit breaker allows me to run a 1,500 watt spacer heater, a 170 watt laptop power adapter, and 2 external monitors all on the same circuit, which would NOT be sustainable with a 15 amp circuit breaker under the 80% load rule.

Answer 2

This question is answered quite well here with references to the pertinent sections of the NEC: Is using 15 amp components on a 20 amp breaker against code?

In short, it's fine to use receptacles and switches rated for 15 amps on a 20 amp branch circuit with a few exceptions.

Answer 3

Yes this question has been answered many time, in short as long as there are at least 2 outlets on a 20 amp circuit 2 single 15 amp or 1 duplex outlet it is legal to use a 20 amp breaker with #12 AWG wire.