I thought wall receptacles required a 20 amp breaker. Am I wrong?
Answer based on the NEC in the US.
In some areas with local amendments to the NEC maybe, but it's not an across the board code requirement.
There are areas in a home that do require 20A circuits, such as bathroom receptacles, laundry receptacle(s), kitchen/DR/pantry receptacles. Other areas such as garages, utility rooms and unfinished basements it is definitely a good idea.
Personally I do most receptacle circuits on 20A, but this is not a hard and fast rule for me.
'T'-bladed 20a receptacles must be on a 20a breaker.
A 15a simplex outlet (where it only accepts a single plug) must be on a 15a breaker.
Standard 15 and 20 amp duplex receptacles (slots for two cords) may be protected by either 15's or 20's.
Is using 15 amp components on a 20 amp breaker against code? Provided it's not a simplex outlet (or as long as there is "2 or more" outlets on the circuit), code allows this.
www.inspectionnews.net, 20 amp duplex receptacle on a 15 amp circuit? Outlets rated for 20a is fine, a 20 amp outlet with a T slot, is not.
The maximum breaker size is determined by the wire size—not the type of outlet. It is okay to install a smaller rated breaker than the wire can carry, though that may be confusing to future owners.
For example, 10 gauge copper normally has a 30 amp breaker. However, it is perfectly fine to use a 25, 20, 15, or even a 10 amp breaker on 10 gauge.
Likewise it is safe (but a bit odd) to install a 50 ampere rated outlet on a 15 amp breakered circuit. One might do this for connector compatibility with say an RV or boat cord especially when you know the maximum load in the vehicle will be within range of the circuit.
But it would not be safe to change the breaker to 50 amps to match the 50 amp outlet if the wire is smaller than 6 gauge.